Pharmacology · Cardiovascular

Ventricular Arrhythmias and Sudden Cardiac Death Prevention

Acute management, ACLS pharmacology, channelopathies, and the ICD vs. drug decision

Hemodynamically stable ventricular tachycardia is treated with IV procainamide (preferred first-line) or IV amiodarone (preferred in structural heart disease or when QTc exceeds 500 ms); hemodynamic instability at any point mandates immediate synchronized cardioversion without delay for drugs.
In pulseless VT/VF, defibrillation is primary — drugs are adjuncts; epinephrine every 3–5 minutes improves coronary perfusion pressure and return of spontaneous circulation but not neurologic survival; amiodarone is first-line after the third shock, with lidocaine as an equivalent alternative (ALPS trial).
Channelopathy drug selection is diagnosis-specific: nadolol is first-line for both Long QT Type 1 and catecholaminergic polymorphic ventricular tachycardia; mexiletine targets the persistent late sodium current defect in Long QT Type 3; quinidine and isoproterenol are used in Brugada syndrome; sodium channel blockers are strictly contraindicated in Brugada regardless of indication.
The ICD is the only intervention proven to reduce sudden cardiac death in primary prevention — the primary prevention threshold is ejection fraction 35% or less, NYHA Class II–III, after 3 months of optimal medical therapy (SCD-HeFT criteria); secondary prevention after a survived cardiac arrest is standard of care.
SCD-HeFT definitively established that amiodarone has no primary prevention mortality benefit in heart failure with reduced ejection fraction; beta-blockers are the only antiarrhythmic class with proven primary prevention mortality benefit; amiodarone reduces ICD shock burden but does not replace the device.

Acute Ventricular Tachycardia and ACLS Pharmacology

Hemodynamically Stable Ventricular Tachycardia

Pharmacologic Termination

Procainamide IV — preferred first-line; Class Ia mechanism; most effective for acute termination; avoid if corrected QT interval over 500 ms or severe left ventricular dysfunction
Amiodarone IV — alternative; preferred in structural heart disease or ventricular tachycardia refractory to procainamide; less hemodynamic risk in impaired ventricle
Unstable at any point — immediate synchronized direct-current cardioversion; do not delay for drugs

Pulseless Ventricular Tachycardia / Ventricular Fibrillation — ACLS

Shock First; Drugs Are Adjuncts

Defibrillation is primary — drugs do not replace shocks
Epinephrine every 3 to 5 minutes — vasopressor; improves coronary perfusion pressure; improves return of spontaneous circulation but not neurologic survival
Amiodarone — first-line antiarrhythmic after 3rd shock (shock-refractory ventricular fibrillation)
Lidocaine — equivalent alternative to amiodarone (ALPS trial finding); use when amiodarone unavailable

Channelopathies — Drug Selection and Avoidance

Syndrome	Trigger	Treatment	Drugs to Avoid
Brugada Syndrome	Rest, sleep, fever	ICD (proven therapy); quinidine for ventricular fibrillation storm and shock reduction; isoproterenol IV for acute storm (bridge to quinidine)	Sodium channel blockers (flecainide, propafenone, procainamide); tricyclic antidepressants; cocaine
Long QT type 1	Exercise, swimming	Beta-blockers (nadolol or atenolol) — highly effective; ICD if breakthrough events	All QT-prolonging drugs; sympathomimetics
Long QT type 2	Sudden auditory stimuli, emotional arousal	Beta-blockers (moderately effective); mexiletine adjunct; silence alarm sounds	All rapid repolarizing potassium channel-blocking drugs (Class Ia, Class III, certain antibiotics, antifungals, antipsychotics)
Long QT type 3	Rest, sleep, bradycardia	Mexiletine (blocks persistent late sodium current — the type 3 defect); ICD strongly recommended; beta-blockers limited benefit	Class Ia and Ic sodium channel blockers; amiodarone; other QT-prolonging agents
Catecholaminergic polymorphic ventricular tachycardia	Exercise, emotional stress, sympathomimetics	Nadolol first-line (non-selective, never stop abruptly); flecainide adjunct when nadolol insufficient; ICD if prior arrest	Sympathomimetics; abrupt beta-blocker withdrawal

Sudden Cardiac Death Prevention — ICD vs. Pharmacology

Primary Tool

Implantable Cardioverter-Defibrillator

Only intervention proven to reduce sudden cardiac death in primary prevention
Primary prevention threshold: ejection fraction 35% or less + New York Heart Association Class II to III + 3 months optimal medical therapy (SCD-HeFT criteria)
Secondary prevention: standard of care after survived cardiac arrest or hemodynamically significant ventricular tachycardia
Adjunct drugs (beta-blockers, amiodarone) reduce shock burden but do not replace the device

Pharmacologic Role

What Drugs Can and Cannot Do

Beta-blockers ONLY — sole antiarrhythmic class with proven mortality benefit (post-myocardial infarction, heart failure with reduced ejection fraction, long QT type 1, catecholaminergic polymorphic ventricular tachycardia)
Amiodarone — effective for acute ventricular arrhythmias and ICD shock reduction; NO primary prevention mortality benefit (SCD-HeFT)
Neurohormonal agents (ACE inhibitors, mineralocorticoid antagonists) — reduce sudden cardiac death via reverse remodeling, not direct antiarrhythmic effects
Antiarrhythmic drugs are adjuncts to ICD — not alternatives to it

The SCD-HeFT Teaching Point

The Sudden Cardiac Death in Heart Failure Trial (2005) definitively established that amiodarone provides no primary prevention mortality benefit compared to placebo in patients with heart failure with reduced ejection fraction. Amiodarone's efficacy for treating acute arrhythmias does not translate into a survival advantage as a primary prevention strategy. The ICD — not amiodarone — is the primary prevention tool. Beta-blockers are the only antiarrhythmic class that reduces mortality in primary prevention.

Suggested References

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