Why does ventricular tachycardia (VT) occur with a low ejection fraction (EF)?

Why Ventricular Tachycardia Occurs with Low Ejection Fraction

Ventricular tachycardia (VT) in patients with low ejection fraction occurs due to structural and electrical remodeling of the heart, creating an arrhythmogenic substrate through myocardial fibrosis, scar formation, and disrupted calcium handling that facilitates re-entry circuits.

Pathophysiological Mechanisms

Structural Remodeling

• Myocardial Fibrosis and Scarring: In hearts with reduced ejection fraction, there is increased fibrosis and scar tissue that creates anatomical barriers to normal electrical conduction 1
• Ventricular Dilation: Progressive ventricular enlargement stretches myocardial fibers, altering their electrical properties and creating areas of heterogeneous conduction 1
• Cellular Disarray: Myocyte disarray and disruption of normal cellular architecture contribute to electrical instability 1

Electrical Remodeling

• Abnormal Calcium Handling: Impaired calcium regulation in failing hearts leads to afterdepolarizations that can trigger arrhythmias 1
• Ion Channel Dysfunction: Changes in ion channel expression and function alter action potential duration and repolarization 1
• Increased Dispersion of Refractoriness: Areas of the myocardium recover at different rates, creating vulnerability to re-entry circuits 1

Neurohormonal Activation

• Sympathetic Hyperactivity: Increased sympathetic tone in heart failure enhances automaticity and triggered activity 1
• Renin-Angiotensin-Aldosterone System: Activation contributes to structural remodeling and fibrosis 1

Clinical Correlations

Relationship Between EF and Arrhythmic Risk

• Lower ejection fraction correlates with higher risk of ventricular arrhythmias 2
• Patients with EF <30% have significantly higher rates of ventricular tachycardia compared to those with higher EFs 2
• The percentage of deaths classified as arrhythmic is similar across EF ranges, but the absolute risk increases as EF decreases 2

Arrhythmogenic Substrate

• Re-entry Circuits: The most common mechanism for sustained VT in low EF is re-entry around areas of scar tissue 1
• Triggered Activity: Calcium overload in failing cardiomyocytes can lead to delayed afterdepolarizations 1
• Enhanced Automaticity: Abnormal pacemaker activity in damaged myocardium 1

Tachycardia-Induced Cardiomyopathy

An important bidirectional relationship exists between tachyarrhythmias and reduced ejection fraction:

• Tachycardia Leading to Cardiomyopathy: Persistent rapid ventricular rates (≥130 beats/min) can produce dilated cardiomyopathy 1
• Reversibility: Control of ventricular rate can lead to significant improvement in ejection fraction (from 25% to 52% in one study) 1
• Mechanisms: Proposed mechanisms include myocardial energy depletion, ischemia, abnormal calcium regulation, and remodeling 1

Clinical Implications

Risk Stratification

• Patients with low EF and nonsustained VT have similar rates of appropriate ICD interventions compared to those with sustained VT/VF history 3
• Inducible ventricular tachyarrhythmias on electrophysiology study identify patients at higher risk of arrhythmic death 2

Management Considerations

• Beta-blockers, ACE inhibitors, and ARBs are recommended for patients with low EF at risk for SCD 1
• Catheter ablation should be considered in patients with low EF and high frequency of ventricular ectopy 1
• ICD implantation is indicated for primary prevention in patients with EF ≤35% and appropriate risk factors 1

Common Pitfalls

• Underestimating Reversibility: Failing to recognize tachycardia-induced cardiomyopathy can miss an opportunity for significant EF improvement with rate control 1
• Timing of EF Assessment: A reduced EF during or shortly after tachycardia may not accurately reflect ventricular function after rate control 1
• Overlooking Non-Arrhythmic Factors: Focusing solely on the arrhythmia without addressing underlying structural heart disease, ischemia, or metabolic factors 1

Understanding the complex relationship between low ejection fraction and ventricular tachycardia is essential for appropriate risk stratification and management of these high-risk patients.