Implantable Defibrillators Prevent Sudden Cardiac Death in Patients With Certain Heart Disorder

08/02/07 Prevention, Research, General

Hypertrophic cardiomyopathy (HCM) is the most common cause of sudden cardiac death in young people, including trained athletes. HCM is a genetic disease in which the heart muscle thickens abnormally, which can interfere with the heart’s electrical system, increasing the risk for life-threatening abnormal heartbeats (arrhythmias). Only in the last few years has the implantable cardioverter-defibrillator (ICD) been systematically used as a potentially life-saving treatment in high-risk patients with HCM, according to background information in the article. An ICD is a device designed to quickly detect a life-threatening, abnormal heart rhythm, and attempt to convert the rhythm back to normal by delivering an electrical shock to the heart. The effectiveness and appropriate selection of HCM patients for this therapy is not certain.

Barry J. Maron, M.D., of the Minneapolis Heart Institute Foundation, Minneapolis, and colleagues examined the clinical risk profile and incidence and effectiveness of ICD intervention in patients with HCM. The researchers analyzed data from a multicenter registry of ICDs implanted between 1986 and 2003 in 506 patients with HCM, average age 42 years. Patients were judged to be at high risk for sudden death. Average follow-up was 3.7 years.

The risk factors the researchers analyzed included:  

• History of premature HCM-related sudden death in one or more first-degree relatives younger than 50 years
  
• Massive left ventricular hypertrophy (enlargement)
  
• Ventricular tachycardia (abnormally rapid heart rhythm)
  
• Previous unexplained syncope (temporary loss of consciousness)

Of the 506 patients, 20 percent experienced one or more appropriate device interventions when the ICD normalized their heart rhythm. The ICD terminated ventricular fibrillation (severely abnormal heart rhythm that results in cardiac arrest) or ventricular tachycardia. Within the study group of patients, researchers found:

• 0.6 percent of patients using the ICD to prevent a second heart attack would need an intervention each year.
• 3.6 percent of patients using the ICD to prevent a first heart attack would need an intervention each year.

"The results of this international, multicenter study show the effectiveness and reliability of the ICD in prevention of sudden cardiac death in high-risk patients with HCM," the authors write. "An important proportion of these device interventions occurred in patients who had undergone prophylactic ICD implantation for a single risk factor. Therefore, a single marker of high-risk status may justify consideration for a primary prevention defibrillator in selected patients with HCM."

Time to first appropriate discharge was up to 10 years, with a 27 percent probability of 5 years or more after implantation. For primary prevention, 35 percent of the patients with appropriate ICD interventions had undergone implantation for only a single risk factor.

"The results of this international, multicenter study show the effectiveness and reliability of the ICD in prevention of sudden cardiac death in high-risk patients with HCM," the authors write. "An important proportion of these device interventions occurred in patients who had undergone prophylactic ICD implantation for a single risk factor. Therefore, a single marker of high-risk status may justify consideration for a primary prevention defibrillator in selected patients with HCM."