What percentage of patients with Hypertrophic Cardiomyopathy (HCM) will develop ventricular arrhythmias?

Ventricular Arrhythmias in Hypertrophic Cardiomyopathy: Prevalence and Risk Assessment

Approximately 90% of adults with hypertrophic cardiomyopathy (HCM) demonstrate ventricular arrhythmias on 24-hour Holter monitoring, with nonsustained ventricular tachycardia (NSVT) occurring in 20-30% of patients. 1

Prevalence of Ventricular Arrhythmias in HCM

The prevalence of ventricular arrhythmias in HCM varies based on the detection method and specific arrhythmia type:

• On routine 24-hour Holter monitoring:

  • 90% of adults show ventricular arrhythmias 1
  • Premature ventricular depolarizations (≥200 in 24 hours): 20% of patients 1
  • Ventricular couplets: >40% of patients 1
  • Nonsustained ventricular tachycardia (NSVT): 20-30% of patients 1

• With insertable cardiac monitors (long-term monitoring):

  • NSVT: 23.3% of patients 2

• Sustained ventricular arrhythmias:

  • Among HCM patients with ICDs, approximately 18% develop sustained ventricular tachyarrhythmias over a 10-year follow-up period 3
  • Annual appropriate ICD intervention rate: 6.8% per year 4

Types of Ventricular Arrhythmias in HCM

Contrary to previous assumptions that ventricular fibrillation (VF) is the predominant life-threatening arrhythmia in HCM, recent evidence shows:

• Sustained monomorphic ventricular tachycardia (VT) is the most common serious arrhythmia (70% of cases) 3
• Antitachycardia pacing can successfully terminate 79% of VT events 3
• Complex ventricular tachyarrhythmias from an electrically unstable myocardial substrate are the most common mechanism of sudden cardiac death (SCD) in HCM 1

Risk Factors for Ventricular Arrhythmias

Several factors increase the risk of ventricular arrhythmias in HCM patients:

• Family history of sudden cardiac death 1, 3
• Personal history of ventricular arrhythmias 3
• Decreased left ventricular ejection fraction 3
• Increased left ventricular end-systolic and end-diastolic diameters 3
• Prior cardiac arrest or sustained VT 1, 5
• Unexplained syncope 1, 5
• Severe left ventricular hypertrophy (≥30 mm) 1
• Abnormal blood pressure response to exercise 5
• Nonsustained VT on monitoring 5

Pathophysiologic Mechanisms

Ventricular arrhythmias in HCM are triggered by:

• Disorganized cardiac muscle cell arrangement 1
• Myocardial replacement scarring (possibly from ischemia) 1
• Abnormal microvasculature 1
• Expanded interstitial collagen compartment 1
• Myocardial fibrosis 5

These structural abnormalities create an electrophysiologically unstable substrate prone to reentrant ventricular tachyarrhythmias.

Clinical Implications and Management

The high prevalence of ventricular arrhythmias in HCM has important implications for patient management:

• Risk stratification: Nonsustained VT on monitoring is an important risk factor for SCD and should be incorporated into risk assessment 1, 5

• ICD therapy: For high-risk patients, ICD implantation is effective in terminating life-threatening ventricular tachyarrhythmias and improving survival 1

• Antiarrhythmic medications: For recurrent ventricular arrhythmias, especially in patients with ICDs:

  • Amiodarone plus beta-blocker is most effective at reducing ICD shocks (only 10.3% of patients experienced shocks at 1 year) 1
  • Beta-blockers are first-line therapy, particularly in pediatric patients 1

• Device programming: Given the high prevalence of monomorphic VT, programming ICDs with antitachycardia pacing capabilities is important 1, 3

The overall annual mortality rate in HCM is approximately 1%, with SCD being the most devastating complication 1. However, with appropriate risk stratification and preventive measures including ICD implantation in high-risk patients, outcomes can be significantly improved.