What are the causes and management options for sudden cardiac death in patients with a history of heart failure, ventricular arrhythmias, or structural heart disease?

Sudden Cardiac Death: Causes and Management

Primary Causes

Sudden cardiac death results predominantly from ventricular tachyarrhythmias (VT/VF) in patients with structural heart disease, though multiple non-arrhythmic mechanisms including acute MI, electrolyte disturbances, pulmonary emboli, and bradyarrhythmias also contribute significantly. 1

Underlying Cardiac Substrates

• Coronary artery disease with prior MI accounts for approximately 65% of SCD cases, with scar-mediated reentry being the predominant arrhythmogenic mechanism 2, 3, 4
• Heart failure with reduced ejection fraction (LVEF ≤35-40%) creates electrical instability and increases SCD risk 6- to 10-fold compared to those without structural disease 1, 2
• Non-ischemic cardiomyopathies including dilated cardiomyopathy, arrhythmogenic right ventricular cardiomyopathy, sarcoidosis, and Chagas disease 3, 4
• Inherited arrhythmogenic disorders such as long QT syndrome, Brugada syndrome, and catecholaminergic polymorphic VT 1

Immediate Triggers

• Acute myocardial ischemia precipitates ionic imbalances and aberrant calcium handling that trigger fatal arrhythmias 1, 5
• Electrolyte disturbances, particularly hypokalemia and hypomagnesemia 1, 6
• Pro-arrhythmic medications including QT-prolonging drugs (quinolones, azithromycin, tricyclic antidepressants) and sodium channel blockers in post-MI patients 1
• Bradyarrhythmias and pulseless supraventricular rhythms occur commonly in advanced heart failure 1

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Management Strategy: A Hierarchical Approach

Step 1: Optimize Medical Therapy for Disease Progression Prevention

All patients with heart failure and LVEF ≤35-40% must receive the triad of ACE inhibitors (or ARBs), beta-blockers, and mineralocorticoid receptor antagonists, as this combination reduces both sudden death and all-cause mortality by 15-35%. 1, 6

• Beta-blockers specifically reduce sudden death incidence through anti-ischemic and anti-arrhythmic effects in post-MI patients and those with heart failure 1, 7
• Aldosterone antagonists (spironolactone or eplerenone) decrease sudden death in early post-MI patients and those with advanced heart failure 1
• ACE inhibitors or ARBs improve reverse remodeling and reduce sudden death rates 1, 6
• Maintain serum potassium 3.5-4.5 mmol/L to prevent electrolyte-triggered arrhythmias 6

Critical Pitfall: Sodium channel blockers (Class IC agents like flecainide, propafenone) are contraindicated in post-MI patients and those with coronary disease, as CAST trial data showed increased mortality 1, 8

Step 2: Secondary Prevention with ICD

For cardiac arrest survivors or patients with documented sustained VT/VF who have otherwise good functional status and prognosis, ICD implantation is mandatory as it definitively reduces mortality. 1, 6, 3

• ICD therapy is the only intervention proven to improve survival in this population 3
• Patients with chronic heart failure, low LVEF, and syncope of unclear origin should also receive ICD given high subsequent sudden death rates 1
• This recommendation applies regardless of age; octogenarians with good functional status benefit equally 1

Step 3: Primary Prevention ICD Criteria

Implant ICD for primary prevention in patients with symptomatic heart failure (NYHA class II-III), LVEF ≤35% after ≥3 months of optimal medical therapy, who are expected to survive ≥1 year with good functional status. 1, 6

Specific Indications:

• Ischemic cardiomyopathy: Wait ≥6 weeks post-MI, then reassess LVEF at 6-12 weeks before ICD decision 1, 6
• Non-ischemic cardiomyopathy: Same LVEF and symptom criteria apply 1
• CRT-D indication: QRS ≥130 ms with LBBB pattern, LVEF ≤30%, NYHA class II, after 3 months optimal medical therapy 1

Critical Pitfall: Do not implant ICD in the immediate post-MI period (first 40 days), as early implantation does not improve outcomes and LVEF may recover 6

Step 4: When NOT to Implant ICD

ICD implantation is contraindicated in patients with progressive, irreversible heart failure decompensation (Stage D) where death is imminent regardless of mode, as this merely shifts death from sudden to progressive heart failure without survival benefit. 1

• Exception: Consider ICD if cardiac transplantation is planned 1
• Assess overall prognosis and functional capacity before any device consideration 1
• Discuss quality-of-life implications (driving restrictions, body image, intimate relations, sports participation) before implantation 1, 6

Step 5: Acute VT/VF Management

For hemodynamically unstable VT or VF, immediate electrical cardioversion is the definitive treatment; for stable monomorphic VT, intravenous procainamide or amiodarone are appropriate. 6

• Immediate coronary angiography for patients presenting with sustained VT/VF in acute setting, as recurrent polymorphic VT/VF indicates incomplete reperfusion 6
• IV amiodarone (150-300 mg bolus) facilitates defibrillation and prevents VT/VF recurrence 6
• IV lidocaine when VT is thought related to myocardial ischemia 6
• Beta-blockers may control recurrent polymorphic VT degenerating into VF 6

Critical Pitfall: Assume wide-QRS tachycardia is VT until proven otherwise; treating presumed SVT with aberrancy when it's actually VT can be fatal 6

Step 6: Role of Antiarrhythmic Drugs

Amiodarone is the only antiarrhythmic drug safe in structural heart disease, but it does NOT reduce mortality and should be reserved for symptom relief from recurrent VT or to reduce ICD shocks—never for primary prevention. 1, 6, 7

• Amiodarone may relieve symptoms from VAs in post-MI survivors but has no mortality benefit 1
• Class IC sodium channel blockers are absolutely contraindicated in coronary disease due to increased mortality 1
• D-sotalol increased mortality in post-MI patients and should be avoided 1
• Most antiarrhythmic agents are negative inotropes that can worsen heart failure 1, 4

Step 7: Catheter Ablation

Catheter ablation dramatically reduces VT recurrence and ICD shocks in patients with structural heart disease and recurrent VT, though mortality benefit remains unproven. 1, 3

• Particularly effective for scar-mediated reentry VT post-MI 1, 3
• Consider ablation when antiarrhythmic drugs fail or are not tolerated 3, 4
• Electrophysiological study guides ablation and confirms mechanism 3

Step 8: Reversible Causes

Always address reversible triggers: complete coronary revascularization for ischemia-related VT/VF, correct electrolyte abnormalities immediately, and discontinue QT-prolonging medications. 1, 6

• Definitive therapy of myocardial ischemia may prevent recurrence of polymorphic VT and VF 1
• Review medication list for pro-arrhythmic drugs (antibiotics, antidepressants, antiarrhythmics) 1
• Optimize heart failure therapy to reduce arrhythmia frequency and tolerance 1

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Special Populations

Post-Heart Transplant

• Sudden death occurs in >10% of cardiac transplant recipients, often related to acute rejection damaging the conduction system or transplant coronary disease 1
• Hyperkalaemia during hemodialysis or plasmapheresis can trigger fatal arrhythmias 1

Wolff-Parkinson-White Syndrome

• Catheter ablation is mandatory for WPW patients resuscitated from sudden cardiac arrest due to AF with rapid accessory pathway conduction causing VF 1

End-of-Life Considerations

• Discuss end-of-life issues and ICD deactivation before implantation and at significant illness trajectory points 1
• In advanced disease, prevention of sudden death may only shift mode of death without improving survival 1