Cardiovascular

Heart failure: ICD and CRT indications

Clinical Overview and When to Suspect Device Candidacy in HF

— Established HFrEF with LVEF ≤35% despite ≥3 months of guideline-directed medical therapy (GDMT)

— NYHA class II–III ambulatory IV symptoms on optimal therapy

— Prior MI ≥40 days out, or nonischemic cardiomyopathy ≥3 months on GDMT

— Survivors of sustained VT/VF or cardiac arrest not due to reversible cause (secondary prevention)

— Wide QRS (≥120 ms, especially LBBB ≥150 ms) prompts CRT consideration

— ARNI (or ACEi/ARB) + evidence-based beta-blocker + MRA + SGLT2 inhibitor

— Add diuretics for congestion; titrate to target doses or maximally tolerated

Board pearl: The single most tested concept is that an ICD is not indicated within 40 days of MI or within 90 days of revascularization/new nonischemic diagnosis — give GDMT time to work and reassess EF first. Early post-MI ICD trials (DINAMIT, IRIS) showed no mortality benefit.

Step 3 management: Document EF, NYHA class, QRS duration, etiology, GDMT doses, and time since MI/diagnosis before ordering an electrophysiology consult.

Core concept: In heart failure with reduced ejection fraction (HFrEF), implantable cardioverter-defibrillators (ICDs) prevent sudden cardiac death (SCD) from ventricular arrhythmias, while cardiac resynchronization therapy (CRT) corrects electrical dyssynchrony to improve symptoms, reverse remodel, and reduce mortality in selected patients with wide QRS.

When to suspect a device candidate:

Step 3 framing: Device decisions are an outpatient longitudinal decision — the question stem will almost always emphasize that GDMT has been maximally titrated and EF re-measured after a waiting period. Premature device placement is a classic distractor.

GDMT before devices (the "four pillars"):

Reassessment EF: Repeat echo at 3 months of optimized therapy — many patients improve EF above 35% and no longer meet ICD criteria.

Life expectancy filter: ICD/CRT only if meaningful survival >1 year with good functional status is expected.

Presentation Patterns and Key History

— Action: refer for primary prevention ICD

— Action: refer for CRT-D (combined CRT pacing + defibrillator)

— Action: secondary prevention ICD regardless of EF

— Time since MI (need ≥40 days) or time since new HF diagnosis (need ≥90 days on GDMT)

— Revascularization timing (need ≥90 days post-CABG/PCI before primary prevention ICD)

— Etiology: ischemic vs nonischemic — affects evidence strength but both qualify

— Rhythm: sinus vs atrial fibrillation (AF lowers CRT response unless rate-controlled or ablated)

— QRS morphology and duration: LBBB ≥150 ms is the strongest CRT indication

— NYHA class on optimal therapy

— Comorbidities limiting 1-year survival (metastatic cancer, advanced dementia, ESRD with poor functional status)

— Syncope of unclear etiology in HFrEF — presume arrhythmic

Key distinction: Primary prevention = no prior sustained VT/VF, qualifying by EF + GDMT criteria. Secondary prevention = survived VT/VF/SCA — qualifies even if EF is preserved (unless fully reversible cause like acute ischemia treated with revascularization).

Board pearl: A patient with VF arrest during acute STEMI who is fully revascularized does not automatically get an ICD — the arrhythmia is considered reversible. Reassess EF at 40 days.

Typical vignette for primary prevention ICD: A 62-year-old man with ischemic cardiomyopathy after anterior MI 6 months ago, on maximally tolerated sacubitril/valsartan, carvedilol, spironolactone, and empagliflozin. Echo shows LVEF 28%. He is NYHA II with stable symptoms.

Typical vignette for CRT-D: A 70-year-old woman with nonischemic dilated cardiomyopathy, LVEF 30%, NYHA III on GDMT for 6 months. ECG: sinus rhythm, LBBB with QRS 160 ms.

Secondary prevention vignette: A 55-year-old resuscitated from out-of-hospital VF arrest, no reversible cause (no STEMI, normal electrolytes, no QT-prolonging drugs).

Key history elements to extract:

Symptoms suggesting arrhythmic risk: palpitations, near-syncope, nonsustained VT on telemetry, family history of SCD.

Physical Exam Findings and Hemodynamic Assessment

— Elevated JVP, hepatojugular reflux

— S3 gallop

— Bibasilar crackles

— Peripheral edema, ascites

— Cool extremities, narrow pulse pressure (low output)

— JVP <8 cm H₂O

— No orthopnea or PND

— Warm, well-perfused extremities

— Stable weight, no recent diuretic up-titration

— NYHA class is determined by symptoms with ordinary activity — document explicitly

— 6-minute walk test or cardiopulmonary exercise testing (peak VO₂) may be used in ambiguous cases

— Hypotension limiting GDMT titration → consider advanced HF referral before device

— Persistent NYHA IV despite optimization → evaluate for LVAD/transplant; CRT-D may still be appropriate as bridge

— Frequent ICD shocks anticipated due to arrhythmia burden → consider VT ablation

— Inspect pocket for hematoma, erythema, dehiscence

— Auscultate for friction rub (lead perforation/pericarditis)

— Check for Twiddler syndrome (patient manipulating device → lead dislodgement)

— Paced rhythm should show biventricular pacing on ECG (narrower QRS than baseline, often with right-axis or superior axis)

— Loss of biventricular pacing (e.g., AF with rapid response) blunts CRT benefit

CCS pearl: Before ordering EP consult for device implantation, document on physical exam: vital signs, JVP, lung exam, peripheral edema, and current weight. Order a recent echo (<3 months), ECG, BMP, CBC, and INR if anticoagulated.

Board pearl: A patient with NYHA IV symptoms who is not ambulatory (inotrope-dependent, bed-bound) is generally not a candidate for ICD primary prevention — life expectancy filter fails.

General HF exam relevant to device decisions: The exam doesn't diagnose ICD/CRT need — it confirms the patient is euvolemic and optimized before device placement.

Signs of residual congestion (delay device, optimize first):

Signs of optimization achieved:

Functional assessment:

Hemodynamic red flags that change the plan:

Device-specific exam after placement:

Pulse and rhythm assessment post-CRT:

Diagnostic Workup — Initial Labs, Imaging, ECG, Biomarkers

— Quantify LVEF (Simpson biplane preferred)

— Repeat after ≥3 months of optimized GDMT before primary prevention ICD

— Assess RV function, valvular disease, LV size

— Document dyssynchrony is not required to indicate CRT — QRS criteria suffice

— Measure QRS duration and morphology

— LBBB ≥150 ms = strongest CRT indication (Class I)

— LBBB 120–149 ms or non-LBBB ≥150 ms = Class IIa

— Non-LBBB <150 ms = generally no CRT benefit (Class III if QRS <120 ms)

— Identify AV block needing pacing — CRT preferred over RV pacing if EF ≤35% (HOT-CRT, BLOCK-HF)

— BMP (K⁺, Mg²⁺, Cr, eGFR) — optimize before procedure

— CBC, coagulation panel

— TSH (rule out reversible cause of cardiomyopathy)

— NT-proBNP or BNP — trend and prognostication, not a device criterion

— HbA1c, iron studies (ferritin, TSAT) — IV iron if deficient

— Coronary angiography or coronary CTA to rule out ischemic etiology (changes prognosis, may identify revascularizable disease)

— Cardiac MRI for nonischemic cardiomyopathy: identifies myocarditis, infiltrative disease (amyloid, sarcoid), LGE pattern predicts arrhythmic risk

— Document nonsustained VT, AF burden

— High PVC burden (>10%) → consider PVC-induced cardiomyopathy (potentially reversible)

Board pearl: Cardiac sarcoidosis and LMNA cardiomyopathy are exceptions where ICD is considered at higher EF thresholds (often EF <50% with risk features) — both have disproportionately high SCD risk.

Step 3 management: Order: TTE, ECG, BMP, CBC, NT-proBNP, TSH, and if not done, coronary evaluation. Re-echo at 3 months on GDMT before EP referral.

Echocardiogram — the cornerstone:

12-lead ECG:

Basic labs:

Etiology workup if not already done:

Holter or event monitor:

Genetic testing: Familial dilated cardiomyopathy, LMNA mutations (high SCD risk → earlier ICD even at EF >35%)

Diagnostic Workup — Advanced or Confirmatory Studies

— Quantifies LV volumes/EF with highest accuracy

— LGE burden and pattern predicts ventricular arrhythmia risk in nonischemic cardiomyopathy

— Identifies sarcoidosis (patchy mid-wall LGE), amyloidosis (diffuse subendocardial), myocarditis

— Increasingly used when ICD decision is borderline (e.g., EF 30–40% nonischemic)

— Not routine for HFrEF primary prevention

— Useful in ischemic cardiomyopathy with EF 36–40% and unexplained syncope or NSVT — inducible sustained VT → ICD

— Also used in suspected arrhythmic syncope

— Peak VO₂ <14 mL/kg/min (or <12 on beta-blocker) supports advanced HF referral

— Helps determine if patient is too sick for ICD alone vs needs transplant/LVAD evaluation

— Required to classify ischemic vs nonischemic etiology

— Revascularization may improve EF — must wait 90 days post-PCI/CABG before re-measuring EF for ICD decision

— FDG-PET shows active inflammation

— Sarcoid → ICD often indicated regardless of EF if LGE present or sustained VT inducible

— LMNA, FLNC, RBM20, PLN, TTN truncating variants — arrhythmogenic phenotypes

— Family screening implications

— ≥40 days post-MI (no revascularization needed)

— ≥90 days post-revascularization (PCI or CABG)

— ≥3 months on GDMT for nonischemic

— Check venous access (prior lines, occlusion) — may need lead extraction planning

— Dental clearance if active infection

— Hold anticoagulation per protocol (warfarin often continued; DOACs held 24–48 h)

Key distinction: EPS-guided ICD decision is largely historical for primary prevention but remains important when EF is borderline (36–40%) with syncope or NSVT. MADIT (original) used inducibility; modern practice relies on EF + GDMT.

Board pearl: In cardiac sarcoidosis, ICD is indicated for EF ≤35%, history of sustained VT/SCA, or unexplained syncope with evidence of myocardial scar — a lower threshold than typical HFrEF.

Cardiac MRI with late gadolinium enhancement (LGE):

Electrophysiology study (EPS):

Cardiopulmonary exercise testing (CPET):

Coronary angiography / CT coronary angiography:

PET or cardiac MRI for sarcoidosis:

Genetic panels:

Repeat echo timing rules (high-yield):

Pre-implant assessment:

Risk Stratification and First-Line Management Logic

— Step 1: Confirm symptomatic HF (NYHA II–III, or NYHA I if ischemic with EF ≤30%)

— Step 2: LVEF ≤35% on optimized GDMT for ≥3 months

— Step 3: ≥40 days post-MI and ≥90 days post-revascularization

— Step 4: Expected meaningful survival >1 year

— Step 5: Patient understands and accepts goals (informed consent, shared decision-making)

— LVEF ≤35% + NYHA II–IV (ambulatory) + sinus rhythm + LBBB ≥150 ms = Class I CRT

— LBBB 120–149 ms OR non-LBBB ≥150 ms = Class IIa

— QRS <120 ms = no CRT (harmful — EchoCRT trial)

— AV block requiring ventricular pacing + EF ≤35% = CRT preferred over RV pacing

— Cardiac sarcoidosis with scar

— LMNA, FLNC, PLN cardiomyopathies

— Hypertrophic cardiomyopathy with risk factors (separate guideline)

— Long QT, Brugada, ARVC (separate, not HF-driven)

— Bridge during the 40-/90-day waiting period in high-risk patients

— Use is selective, not routine (VEST trial: no mortality reduction)

— Reasonable for newly diagnosed cardiomyopathy with very low EF awaiting recovery

— NYHA IV nonambulatory without LVAD/transplant plan

— Life expectancy <1 year (metastatic cancer, advanced dementia)

— Active infection (bacteremia, endocarditis) — treat first

— Patient declines after informed discussion

Step 3 management: When a stem describes a newly diagnosed HFrEF patient, the correct next step is GDMT optimization and re-echo at 3 months, not immediate device referral. This is the single most common Step 3 trap.

Board pearl: CRT benefit is largest in women, LBBB morphology, QRS ≥150 ms, and nonischemic etiology. Men with non-LBBB and QRS 120–149 ms derive minimal benefit.

The decision tree for primary prevention ICD in HFrEF:

CRT decision tree (added on top of ICD criteria):

Special arrhythmic risk modifiers (consider ICD at higher EF):

Wearable cardioverter-defibrillator (WCD, "LifeVest"):

Reasons to defer or not implant:

Pharmacotherapy — Optimizing GDMT Before and After Device

— ARNI (sacubitril/valsartan) preferred over ACEi/ARB (PARADIGM-HF): start 49/51 mg BID, titrate to 97/103 mg BID; washout 36 h from ACEi

— Beta-blocker with mortality data: carvedilol, metoprolol succinate, or bisoprolol — titrate every 2 weeks to target

— MRA: spironolactone 25–50 mg daily or eplerenone 25–50 mg daily — monitor K⁺ and Cr; hold if K⁺ >5.0 or eGFR <30

— SGLT2 inhibitor: dapagliflozin or empagliflozin 10 mg daily — benefit regardless of diabetes status

— Loop diuretic (furosemide, torsemide, bumetanide) for congestion — does not improve mortality

— Hydralazine + isosorbide dinitrate in self-identified Black patients with NYHA III–IV on GDMT (A-HeFT)

— Ivabradine if sinus rhythm and HR ≥70 on max beta-blocker

— Vericiguat for worsening HF despite GDMT (VICTORIA)

— Iron repletion (IV ferric carboxymaltose) if iron deficient

— Increase doses every 2 weeks as tolerated

— Recheck BMP within 1–2 weeks of starting/increasing ACEi/ARB/ARNI, MRA, or SGLT2i

— Target doses prioritized; if not achievable, add the next pillar at lower doses rather than maximizing one

— NSAIDs (Na/water retention, AKI)

— Non-dihydropyridine CCBs (verapamil, diltiazem) — negative inotropy

— Class I antiarrhythmics

— Thiazolidinediones (pioglitazone, rosiglitazone) — fluid retention

— Saxagliptin (HF hospitalization risk)

— Amiodarone or sotalol to reduce ICD shock burden if recurrent VT

— VT ablation increasingly preferred to amiodarone (PAUSE-SCD, VANISH trials)

Board pearl: Always restate that GDMT is maximally titrated for ≥3 months before declaring a patient an ICD candidate. The stem will reward you for delaying the device and adding the missing pillar.

Step 3 management: Re-echo at 3 months. If EF improves >35%, hold off on ICD and continue GDMT — many recover.

The four pillars of HFrEF GDMT (must be optimized before primary prevention ICD):

Additional agents per phenotype:

Titration rules:

Drugs to avoid in HFrEF:

Antiarrhythmic adjuncts post-ICD:

Procedures — ICD and CRT Implantation Details

— Single-chamber ICD: RV lead only — used when no pacing needs and no AF

— Dual-chamber ICD: RA + RV leads — for patients with sinus node dysfunction, AV block, or paroxysmal AF needing atrial info

— CRT-P (pacemaker): biventricular pacing without defibrillator — for patients meeting CRT criteria but not ICD criteria (e.g., life expectancy concerns)

— CRT-D: biventricular pacing + defibrillator — most common in HFrEF + LBBB

— Subcutaneous ICD (S-ICD): no transvenous leads; for patients without pacing needs, prior infection, or limited venous access; cannot provide antitachycardia pacing or CRT

— Pre-op: hold DOACs 24–48 h; continue warfarin (BRUISE-CONTROL trial: continued warfarin had fewer hematomas than bridging)

— Antibiotic prophylaxis: cefazolin within 60 min of incision

— Left infraclavicular pocket (right if left-handed or AV fistula plans)

— Leads via axillary/subclavian/cephalic vein

— Defibrillation threshold testing rarely performed routinely now

— Pneumothorax (1–2%)

— Pocket hematoma — risk increased by bridging anticoagulation

— Lead dislodgement (especially LV lead — coronary sinus anatomy variable)

— Cardiac perforation/tamponade

— Infection (~1–2%)

— Chest X-ray to confirm lead position, exclude pneumothorax

— Device interrogation before discharge

— Arm sling 24–48 h; avoid overhead activity 2–4 weeks

— Driving restrictions (see ethics chunk)

CCS pearl: Order CXR PA/lateral and device interrogation immediately post-implant. Discharge with wound care instructions, arm restrictions, and EP follow-up in 2 weeks.

Board pearl: S-ICD is the answer when the stem features a young patient, prior device infection, hemodialysis with poor venous access, or no pacing needs — but disqualifies if CRT or antitachycardia pacing is needed.

Device types:

Procedural workflow:

Common procedural complications:

Post-implant care:

Generator changes: Battery life 5–10 years; replacement is a smaller procedure but carries infection risk.

Lead extraction: For infection, malfunction, or upgrade — performed at specialized centers using laser or rotational sheaths; mortality 0.1–0.5%.

Special Populations — Elderly and Renal/Hepatic Impairment

— Mortality benefit of primary prevention ICD attenuates with age and comorbidity (DANISH trial in nonischemic CM: no overall benefit, but benefit in patients <68)

— Use shared decision-making — discuss competing risks of death, lower likelihood of arrhythmic SCD vs pump failure death

— Frailty assessment (gait speed, grip strength) more predictive than age alone

— CRT benefit largely preserved in elderly if QRS/LBBB criteria met — symptom improvement is meaningful

— eGFR <30 or dialysis: ICD benefit uncertain; competing mortality from CV death and infection risk is high

— Dialysis patients have higher lead infection rates and higher SCD risk but trials (ICD2) showed no mortality benefit in dialysis

— Consider S-ICD to preserve upper extremity vasculature for fistula creation

— Adjust GDMT: ARNI/ACEi/ARB may worsen eGFR transiently — acceptable if <30% drop; hold if K⁺ >5.5

— SGLT2i: now indicated down to eGFR 20–25, continue on dialysis is investigational

— Cirrhosis with cardiac cirrhosis or cirrhotic cardiomyopathy — device decision individualized

— Beta-blockers caution if hepatic encephalopathy or severe ascites; carvedilol metabolized hepatically

— Spironolactone often already used for ascites — monitor K⁺

— Coagulopathy increases procedural bleeding risk

— Strong indication for SGLT2 inhibitor regardless of HF

— Avoid TZDs and saxagliptin

— Higher procedural complications, lead positioning challenges

— Weight loss can improve EF and reduce arrhythmia burden

Key distinction: In dialysis patients, primary prevention ICD has not shown mortality benefit — competing causes of death dominate. Secondary prevention ICD (post-VT/VF) is still indicated.

Step 3 management: For an 82-year-old with EF 30%, ischemic CM, NYHA II, optimized GDMT, and significant frailty/comorbidities — document shared decision-making; mortality benefit may not exceed procedural and competing risks. CRT-P (without defibrillator) may be reasonable if QRS qualifies.

Elderly patients (>75–80 years):

Chronic kidney disease:

Hepatic impairment:

Diabetes:

Obesity:

Special Populations — Pregnancy, Pediatrics, and Recovered EF

— PPCM presents late pregnancy to 5 months postpartum

— Many recover EF within 6–12 months with GDMT (excluding ARNI/ACEi/ARB during pregnancy — use hydralazine/nitrates + beta-blocker; switch postpartum if not breastfeeding limits)

— Wearable cardioverter-defibrillator (LifeVest) during the recovery window is preferred over permanent ICD

— Permanent ICD only if EF remains ≤35% after 3–6 months of GDMT post-delivery

— Bromocriptine adjunct controversial; anticoagulation if EF <30% (high thromboembolism risk)

— ICD indications follow adult criteria for EF-based decisions but congenital substrate (tetralogy of Fallot, single ventricle) has unique arrhythmia risks

— Generally referred to specialized pediatric EP

— DANISH trial showed no overall mortality benefit of ICD in nonischemic CM on GDMT (still improves SCD); however current guidelines retain Class I/IIa for EF ≤35% NYHA II–III

— Reassess EF at 3–6 months — meaningful recovery in 30–40%

— ICD does not preclude moderate exercise; competitive contact sports historically restricted but evolving (LIVE-HCM, ICD Sports Safety Registry support shared decision-making)

— Do not withdraw GDMT — discontinuation often leads to recurrence (TRED-HF trial)

— If ICD was placed, continued therapy at generator change is reasonable but individualized

— Consider downgrading from CRT-D to CRT-P at generator change in selected patients

— ICD benefit unclear; arrhythmic death often pulseless electrical activity, not VT/VF

— Treat with tafamidis (ATTR) or chemo (AL); device decisions individualized

Board pearl: A peripartum cardiomyopathy patient with EF 25% should get a wearable defibrillator during recovery, not an immediate permanent ICD — many recover.

Key distinction: In TRED-HF, withdrawing GDMT from recovered dilated CM patients caused relapse in ~40% within 6 months — continue GDMT indefinitely even after EF normalizes.

Pregnancy and peripartum cardiomyopathy (PPCM):

Pediatric and congenital heart disease:

Recently diagnosed nonischemic cardiomyopathy:

Athletes and active patients:

Patients with recovered EF (>35–40%) on GDMT:

Cardiac amyloidosis:

Complications and Adverse Outcomes

— Pneumothorax/hemothorax (1–2%)

— Cardiac perforation, tamponade (<1%)

— Pocket hematoma (2–5%; higher with bridging anticoagulation)

— Lead dislodgement (especially LV lead via coronary sinus)

— Vascular injury, air embolism

— Pocket infection or systemic CIED infection: 1–2% lifetime, higher with revisions

— Staphylococci predominate (S. aureus, CoNS)

— Any S. aureus bacteremia in a CIED patient → assume device infection until proven otherwise (TEE, complete extraction)

— Treatment: complete hardware extraction + prolonged IV antibiotics; reimplant on contralateral side after clearance

— Fracture, insulation failure, dislodgement

— Presents as inappropriate shocks, failure to capture, oversensing

— Recalled leads (historical: Sprint Fidelis, Riata) — periodic monitoring critical

— Causes: AF/SVT with rapid response, T-wave oversensing, lead noise, EMI

— Major source of distress and PTSD-like symptoms

— Reduced by higher detection rate cutoffs (>200 bpm) and longer detection durations (MADIT-RIT)

— Manage: reprogram, rate-control AF, beta-blocker/amiodarone, VT ablation

— Even appropriate shocks carry psychological burden and predict worse outcomes

— Recurrent VT despite therapy → consider catheter ablation

— Patient manipulates device → lead retraction/coiling → loss of capture

— Higher in elderly, obese, cognitively impaired patients

— Causes: scar at LV pacing site, suboptimal lead position, low biventricular pacing percentage (<92%), AF with rapid response

— Optimize: reprogram AV/VV delays, control AF (rate, ablation), consider LV lead repositioning or His/LBB pacing

CCS pearl: Patient with fever and ICD → blood cultures × 2, TTE → if positive cultures or vegetations, TEE and infectious disease + EP consult for complete extraction.

Board pearl: S. aureus bacteremia + CIED = extract the device. This is one of the most testable infectious disease/cardiology crossover points.

Procedural complications (acute):

Infection:

Lead malfunction:

Inappropriate shocks:

Appropriate shocks:

Twiddler syndrome:

Venous occlusion: Subclavian/axillary thrombosis, SVC syndrome with multiple leads

CRT non-response (~30% of patients):

When to Escalate Care — Inpatient Triage and Consults

— Single appropriate shock, patient stable, no recurrent symptoms: Outpatient EP interrogation within 24–48 hours acceptable

— Multiple shocks (≥2 in 24 h) = electrical storm: Admit to CCU, IV beta-blocker (esmolol), amiodarone or lidocaine, sedation; urgent EP consult

— Inappropriate shocks: Urgent device interrogation; consider magnet application (suspends therapy but not pacing) while arranging EP evaluation

— IV access, telemetry, oxygen, IV beta-blockade

— Amiodarone load (150 mg IV then drip) or lidocaine

— Sedation (propofol, midazolam) reduces sympathetic drive and shock perception

— Correct electrolytes: K⁺ >4.0, Mg²⁺ >2.0

— Treat ischemia: troponin, ECG, possible cath

— Consider stellate ganglion block or VT ablation

— Admit; blood cultures × 2 from separate sites

— Empiric vancomycin (cover MRSA)

— TEE for vegetations

— ID + EP consults for extraction planning

— Check device interrogation for biventricular pacing percentage — target >92%

— Low BiV% from AF, frequent PVCs, or programming issues → rate control or ablation

— If pacing >40% anticipated and EF ≤35% → upgrade to CRT rather than RV-only pacemaker (BLOCK-HF)

— Could be non-arrhythmic (orthostasis from GDMT, vasovagal) or under-detected arrhythmia

— Admit if hemodynamically significant; interrogate device

— Frequent ICD shocks despite optimal therapy

— NYHA IV on inotropes

— Cardiorenal syndrome refractory to diuresis

— Peak VO₂ <14 mL/kg/min

CCS pearl: For electrical storm: admit to CCU, IV amiodarone, IV beta-blocker, electrolyte repletion, EP consult, consider intubation/sedation, and VT ablation referral.

Step 3 management: A patient with one appropriate ICD shock and resolution of symptoms can be evaluated outpatient within 1–2 days — admission not mandatory unless storm or hemodynamic instability.

Patients with ICD presenting with shocks:

Electrical storm management (CCS-friendly):

CIED infection:

Decompensated HF in CRT patient:

New AV block in HFrEF patient on GDMT:

Syncope in ICD patient without shock:

When to call advanced HF / transplant team:

Key Differentials — Same-Category (Other HF / Arrhythmic Substrates)

— Ischemic cardiomyopathy (post-MI, multivessel CAD): strongest evidence for ICD (MADIT-II, SCD-HeFT subgroup); ICD = Class I if EF ≤35% NYHA II–III or EF ≤30% NYHA I

— Nonischemic dilated cardiomyopathy: ICD Class I/IIa per guidelines despite DANISH; benefit clearer in younger patients

— Hypertrophic cardiomyopathy: ICD by risk score (HCM Risk-SCD), not EF — septal thickness ≥30 mm, family history of SCD, unexplained syncope, NSVT, abnormal BP response

— Cardiac sarcoidosis: ICD if EF ≤35%, sustained VT, syncope with scar, or inducible VT — lower thresholds

— Arrhythmogenic right ventricular cardiomyopathy (ARVC): ICD by risk factors (prior arrest, sustained VT, syncope, severe RV/LV dysfunction)

— Channelopathies (long QT, Brugada, CPVT): ICD for SCD survivors or high-risk genotype/phenotype combinations

— LMNA cardiomyopathy: ICD at higher EF thresholds (EF <45% + risk factors)

— Tachycardia-induced cardiomyopathy: AF, atrial flutter, frequent PVCs (>10–20% burden) — treat arrhythmia, EF often recovers in 3–6 months → no permanent ICD

— Stress (takotsubo) cardiomyopathy: typically recovers in weeks; no ICD

— Myocarditis: acute phase often recovers; defer ICD decision 3–6 months

— Alcohol- or substance-induced: cessation often leads to recovery

— Thyroid- or nutritional-deficiency (selenium, thiamine) cardiomyopathy: treat underlying cause

— LBBB ≥150 ms: strongest CRT benefit

— Non-LBBB ≥150 ms: modest benefit

— RBBB: minimal benefit (often answered as "do not recommend CRT")

— Narrow QRS (<120 ms): no CRT (harmful)

Key distinction: PVC-induced cardiomyopathy (PVC burden >10–20%) is reversible with ablation — do not jump to ICD. Address the PVCs and re-image at 3–6 months.

Board pearl: HCM and ARVC use risk-stratification scores, not EF, to drive ICD decisions. HFrEF uses EF + GDMT + waiting period.

Differentiating among device-eligible substrates:

Reversible vs irreversible cardiomyopathy:

Peripartum cardiomyopathy: WCD bridge, defer permanent device

CRT eligibility differentiators:

Key Differentials — Other-Category Causes of Symptoms/Findings

— Constrictive pericarditis: dyspnea, edema, elevated JVP with Kussmaul sign, pericardial knock; preserved EF; CT/MRI shows thickened pericardium → pericardiectomy, not ICD

— Restrictive cardiomyopathy (amyloidosis, hemochromatosis, sarcoidosis): preserved or mildly reduced EF; biventricular thickening; treat underlying cause

— Cardiac amyloidosis: tafamidis (ATTR-CA), chemo (AL); ICD benefit limited because death often from PEA

— Severe valvular disease (AS, MR): correct valve (TAVR, MitraClip, surgery) before considering device — EF may recover

— Vasovagal syncope, orthostatic syncope in HF patients on GDMT — does not equal arrhythmic syncope; tilt-table or careful history

— Pulmonary embolism: dyspnea, hypotension, RV strain on echo — not an ICD problem; anticoagulate

— Acute coronary syndrome: ischemic VT during STEMI is reversible — revascularize, do not implant during index admission

— Right bundle branch block alone: not LBBB; CRT benefit minimal

— Paced rhythm via RV lead in patient with pacemaker: if pacing burden high and EF declines → consider CRT upgrade (BLOCK-HF, BIOPACE)

— Electromagnetic interference (MRI without conditional protocol, electrocautery, TENS, certain occupational exposures)

— Lead fracture or insulation breach causing noise

— T-wave oversensing

— No ICD indication based on EF alone

— Treat with SGLT2 inhibitor (Class I), MRA, ARNI as supported by EMPEROR-Preserved, DELIVER, PARAGON-HF

— Address comorbidities: HTN, AF, obesity, sleep apnea

— No primary prevention ICD by EF criteria

— GDMT similar to HFrEF; reassess EF — may evolve

Board pearl: MRI in CIED patients is now safe with MR-conditional devices following a standardized protocol; legacy non-conditional devices can also be imaged at specialized centers (MagnaSafe registry data).

Key distinction: Cardiac amyloidosis patients with EF ≤35% often do not benefit from primary prevention ICD — mortality is driven by pump failure and PEA arrest, not VT/VF.

Mimics of HFrEF that change the management plan:

Mimics of arrhythmic events:

Wide QRS without CRT benefit:

Other causes of inappropriate shocks (not arrhythmia):

HFpEF (EF ≥50%):

HFmrEF (EF 41–49%):

Secondary Prevention, Discharge Medications, and Long-Term Plan

— ARNI (or ACEi/ARB), evidence-based beta-blocker, MRA, SGLT2 inhibitor — at target or maximally tolerated doses

— Loop diuretic for congestion

— Hydralazine/ISDN add-on as indicated

— Iron repletion for deficiency

— Amiodarone or sotalol if recurrent VT/shocks

— Catheter ablation increasingly first-line over chronic amiodarone (VANISH, PAUSE-SCD)

— Beta-blocker remains foundational

— DOAC or warfarin if AF (per CHA₂DS₂-VASc)

— LV thrombus on imaging → anticoagulate ≥3 months

— Aggressive rate control (target resting HR <80) to maintain biventricular pacing >92%

— AV nodal ablation if rate control fails — guarantees BiV pacing

— Rhythm control (cardioversion, ablation) preferred when feasible

— Device card, manufacturer info, model/serial

— Wound care: keep dry 5–7 days, no soaking 2 weeks

— Arm restrictions: no overhead activity, lifting >10 lb for 2–4 weeks (avoid lead dislodgement)

— MRI safety: conditional vs non-conditional documented

— Avoid sustained close proximity to strong magnetic fields, certain industrial equipment

— Cell phones: use opposite ear/pocket

— TSA/airport screening: hand wand instead of metal detector — show device card

— BP target <130/80

— LDL <70 (or per ASCVD); statin

— Diabetes: HbA1c individualized

— Tobacco cessation, alcohol moderation, weight management

— Sleep apnea screening and treatment

Step 3 management: At discharge, schedule device interrogation in 2 weeks, EP follow-up in 4–6 weeks, HF clinic in 1–2 weeks with BMP, and ensure GDMT continues with explicit titration plan.

Board pearl: Continue GDMT even if EF normalizes — TRED-HF showed relapse after withdrawal.

Continue and optimize GDMT indefinitely after device:

Antiarrhythmic considerations:

Anticoagulation:

Atrial fibrillation in CRT patients:

Discharge checklist for newly implanted CIED:

Vaccination: Annual influenza, pneumococcal series, COVID-19 boosters

Risk-factor modification:

Cardiac rehabilitation: Class I recommendation post-device in stable HFrEF; improves functional capacity, quality of life, and reduces hospitalizations.

Follow-Up, Monitoring, and Rehabilitation

— In-person interrogation at 2 weeks post-implant (wound check, lead parameters)

— Then every 3–12 months depending on device and remote monitoring availability

— Remote monitoring is Class I — reduces in-person visits, detects lead/battery issues early, identifies AF and arrhythmias

— Battery longevity assessments annually

— Within 7–14 days of any HF hospitalization (reduces 30-day readmissions)

— Then every 1–3 months while titrating GDMT

— Stable patients: every 3–6 months

— BMP within 1–2 weeks of GDMT changes and at routine visits

— NT-proBNP trends for response and risk

— HbA1c, iron studies annually

— Repeat at 3 months post-implant of CRT to assess remodeling response

— Then as clinically indicated; annual not mandatory unless symptom change

— Refer all stable HFrEF patients (HF-ACTION trial)

— 36 sessions covered by Medicare for HFrEF NYHA II–III

— Improves peak VO₂, quality of life, and reduces all-cause mortality and HF hospitalization

— Sodium restriction <2–3 g/day in symptomatic HF

— Fluid restriction 1.5–2 L/day if hyponatremic or refractory congestion

— Daily weights; alert for >2 lb/day or >5 lb/week gain

— Activity as tolerated; resistance and aerobic training

— Tobacco and substance cessation

— Screen for depression (PHQ-9), anxiety

— Counsel about shock anxiety after appropriate or inappropriate shocks

— Support groups, mental health referral as needed

— Primary prevention ICD without shock: typically 1 week restriction post-implant

— Secondary prevention ICD or after appropriate shock: 6 months without further events (varies by state law and commercial vs private driving)

CCS pearl: Order remote monitoring enrollment at discharge — it improves outcomes and is a Class I recommendation.

Board pearl: Post-HF-hospitalization follow-up within 7 days is the single most impactful intervention for reducing 30-day readmissions.

Device follow-up schedule:

HF clinic follow-up:

Monitoring labs:

Echocardiography:

Cardiac rehabilitation:

Lifestyle counseling:

Psychosocial support:

Driving restrictions after device:

End-of-life planning: Revisit goals of care at each transition; deactivation discussion (see ethics chunk).

Ethical, Legal, and Patient Safety Considerations

— Must discuss procedural risks (pneumothorax, bleeding, infection, lead complications)

— Must discuss psychological burden of shocks and risk of inappropriate shocks

— Must discuss that ICD prevents sudden death but does not improve symptoms (CRT does)

— Must discuss option to decline the device — autonomy preserved

— Must discuss deactivation as an option at end of life — withholding/withdrawing therapy is ethically equivalent and legally permissible

— Patients with advanced cancer, hospice enrollment, or terminal illness can request ICD therapies be turned off

— Deactivation does not equal euthanasia; it allows natural death from underlying disease

— Pacing function can be left on for symptom control if patient pacemaker-dependent

— Programming change is reversible; magnet application temporarily disables shocks if reprogramming unavailable

— Address proactively, ideally before crisis

— State-specific laws; commercial drivers (CDL) typically disqualified after ICD implant (FMCSA rules)

— Counsel patients explicitly and document

— Elderly with comorbidities, dialysis patients, advanced HF without transplant candidacy

— Use validated decision aids; document the conversation

— Device manufacturers report safety/recall data via FDA MAUDE

— National Cardiovascular Data Registry (NCDR) ICD Registry — many institutions participate

— Hand-off after implant: primary care must know device type, MRI status, manufacturer, and follow-up plan

— Medication reconciliation: continue GDMT; ensure no NSAIDs, no negative inotropes

— EHR alerts for MRI-conditional vs non-conditional status

— Discharge readback with family/caregiver

— Magnet over ICD: suspends defibrillation therapy but does not affect pacing

— Magnet over pacemaker: asynchronous pacing

— Useful intraoperatively (electrocautery) and to terminate inappropriate shocks acutely

Step 3 management: A hospice-enrolled HFrEF patient receiving ICD shocks should be offered deactivation — discuss with patient/surrogate, document, and have EP or trained clinician reprogram. Apply a magnet over the generator as a bridge.

Board pearl: ICD deactivation at end of life is ethically and legally appropriate when consistent with goals of care — this is a commonly tested Step 3 ethics scenario.

Informed consent specifics for ICD/CRT:

End-of-life ICD deactivation:

Driving and occupational restrictions:

Shared decision-making for borderline cases:

Mandatory reporting and registries:

Patient safety / transition-of-care risks:

Magnet response (high-yield):

Advance directives: Should explicitly address ICD therapies separately from CPR/intubation preferences.

High-Yield Associations and Rapid-Fire Clinical Facts

— MADIT-II: ICD in post-MI EF ≤30% — established primary prevention

— SCD-HeFT: ICD in NYHA II–III EF ≤35% (ischemic and nonischemic) — broadest support

— DINAMIT / IRIS: No benefit of early ICD post-MI (<40 days) → established the 40-day waiting period

— DANISH: Nonischemic CM ICD — no overall mortality benefit but reduces SCD; benefit in younger patients

— MADIT-CRT, RAFT, CARE-HF, COMPANION: CRT benefit in NYHA II–IV with wide QRS

— EchoCRT: CRT harmful in narrow QRS (<130 ms) — do not implant

— BLOCK-HF: CRT preferred over RV pacing in EF ≤50% with AV block

— MADIT-RIT: Higher detection rates reduce inappropriate shocks

— BRUISE-CONTROL: Continued warfarin safer than bridging for hematoma prevention

— VANISH, PAUSE-SCD: VT ablation reduces recurrent ICD shocks

— EF threshold: ≤35% (≤30% for NYHA I ischemic)

— Post-MI waiting: 40 days

— Post-revascularization waiting: 90 days

— New nonischemic CM waiting: ≥3 months on GDMT

— QRS for CRT Class I: ≥150 ms with LBBB

— CRT biventricular pacing target: ≥92%

— Expected meaningful survival: >1 year

— Better: female, LBBB, QRS ≥150 ms, nonischemic, less scar, sinus rhythm

— Worse: male, non-LBBB, QRS <150 ms, ischemic with extensive scar, AF

— S. aureus bacteremia in CIED patient → assume infection

— Pocket erythema, drainage, dehiscence → infected until proven otherwise

— Over ICD: disables shocks, keeps pacing

— Over pacemaker: asynchronous pacing at magnet rate

— Young patients, no pacing needs, prior infections, vascular access limits

— Disqualifies if: need for ATP, pacing, or CRT

— MR-conditional devices: scan per protocol

— Non-conditional: scan possible at specialized centers with monitoring

Board pearl: "EF ≤35%, on GDMT ≥3 months, ≥40 days post-MI or ≥90 days post-revasc" — memorize this exact phrasing; it's the Class I primary prevention ICD trigger.

Trial-to-indication mapping (must-know):

Numeric anchors:

CRT response predictors:

CIED infection clues:

Magnet pearls:

S-ICD use cases:

MRI safety:

Board Question Stem Patterns

— Stem: 58yo with anterior MI 2 weeks ago, EF 25%, NYHA II on early HF meds. Asks next step.

— Answer: Optimize GDMT and reassess EF at 40 days/3 months, not immediate ICD. Wearable defibrillator may be reasonable.

— Stem: 65yo, ischemic CM, MI 8 months ago, on ARNI/carvedilol/spironolactone/empagliflozin × 4 months, EF 28%, NYHA II.

— Answer: Refer for primary prevention ICD.

— Stem: 68yo, nonischemic DCM, on optimized GDMT × 6 months, EF 30%, NYHA III, ECG shows LBBB QRS 158 ms, sinus rhythm.

— Answer: CRT-D.

— Stem: HFrEF EF 25% on GDMT, QRS 108 ms, NYHA III.

— Answer: No CRT (EchoCRT showed harm). ICD only.

— Stem: 50yo with new HF, EF 25%, PVC burden 25% on Holter, on initial GDMT.

— Answer: PVC ablation, reassess EF — not immediate ICD.

— Stem: 32yo, 2 months postpartum, EF 25%, NYHA II on hydralazine/nitrate/beta-blocker.

— Answer: Wearable cardioverter-defibrillator; reassess EF at 3–6 months.

— Stem: 60yo resuscitated from VF arrest, no STEMI, normal K⁺/Mg²⁺, EF 45%.

— Answer: Secondary prevention ICD regardless of EF.

— Stem: ICD patient with S. aureus bacteremia, TEE shows lead vegetation.

— Answer: Complete device extraction + prolonged IV antibiotics.

— Stem: 70yo with ICD, 4 shocks in 12 hours, sustained VT episodes.

— Answer: Admit to CCU, IV beta-blocker + amiodarone, EP consult for ablation.

— Stem: Terminal cancer patient with ICD, family asks about shocks during dying.

— Answer: Discuss and offer deactivation; reprogram (or magnet bridge).

— Stem: EF 30%, NYHA II, new complete heart block.

— Answer: CRT (BLOCK-HF), not RV-only pacemaker.

— Stem: ICD placed for EF 25%, now EF 50% on GDMT.

— Answer: Continue GDMT; do not withdraw (TRED-HF).

Board pearl: When in doubt, the answer is usually "optimize GDMT and reassess EF" — the test rewards patience over procedures.

Pattern 1 — "Premature device" trap:

Pattern 2 — Classic primary prevention ICD:

Pattern 3 — Classic CRT-D:

Pattern 4 — Narrow QRS distractor:

Pattern 5 — Reversible cardiomyopathy:

Pattern 6 — Peripartum CM:

Pattern 7 — Secondary prevention:

Pattern 8 — CIED infection:

Pattern 9 — Electrical storm:

Pattern 10 — End-of-life deactivation:

Pattern 11 — AV block in HFrEF needing pacing:

Pattern 12 — Recovered EF:

One-Line Recap

The bottom line: Implantable cardioverter-defibrillators reduce sudden cardiac death in patients with LVEF ≤35% on optimized GDMT for ≥3 months (≥40 days post-MI, ≥90 days post-revascularization) with expected meaningful survival >1 year, and CRT is added when QRS is ≥150 ms with LBBB morphology — all decisions hinge on completing GDMT first and reassessing EF before referral.

— Primary prevention ICD criteria: EF ≤35%, NYHA II–III (or NYHA I ischemic with EF ≤30%), ≥40 days post-MI, ≥90 days post-revascularization, ≥3 months on optimized GDMT, life expectancy >1 year. Secondary prevention ICD: any SCA/sustained VT survivor not from fully reversible cause.

— CRT criteria: EF ≤35% + NYHA II–IV ambulatory + sinus rhythm + LBBB ≥150 ms = Class I. Non-LBBB or QRS 120–149 ms = Class IIa. QRS <120 ms = harmful (do not implant). CRT preferred over RV pacing when EF ≤50% and high pacing burden expected (BLOCK-HF).

— GDMT first, devices second: Four pillars (ARNI, evidence-based beta-blocker, MRA, SGLT2 inhibitor) must be titrated and EF re-measured at 3 months before primary prevention ICD. Many patients recover EF and no longer qualify; continue GDMT even if EF normalizes (TRED-HF).

— High-yield clinical traps: Newly diagnosed HF or recent MI → wait and optimize, do not implant. S. aureus bacteremia in CIED patient → extract device. PVC-induced cardiomyopathy → ablate, not implant. Peripartum CM → wearable defibrillator bridge. Terminal illness → discuss and honor deactivation requests as an ethical, legal, and compassionate end-of-life option.

Board pearl: The most testable phrase in this topic is "reassess LVEF after at least 3 months of optimized GDMT" — write it on your scratch paper before reading any HF device stem.

Step 3 management: Document EF, NYHA, QRS duration/morphology, etiology, time since MI/revascularization, GDMT regimen with doses, comorbidities, and shared decision-making — then refer to electrophysiology.

Rapid recap bullets: