Global Study Shows Success of ICDs for Preventing Sudden Death in HCM

Implantable cardioverter-defibrillators (ICDs) have proven beneficial when used in the broader population of patients with hypertrophic cardiomyopathy (HCM) over a span of more than three decades, according to data covering six continents.

Over a mean follow-up of about 7 years, the proportion of HCM patients who received an appropriate ICD shock for a ventricular tachyarrhythmia was 16%, with a higher percentage among patients who had their device for secondary versus primary prevention (35% vs 15%), researchers led by Ethan Rowin, MD (Lahey Hospital and Medical Center, Burlington, MA), report in a paper published recently in Circulation.

Survival rates at 5 and 10 years were 95.9% and 91.7%, respectively, in primary prevention patients and 92.9% and 86.1%, respectively, in secondary prevention patients.

Eleven patients with a primary prevention ICD died suddenly during follow-up, which equates to a device failure rate of 2.4% of those with life-threatening ventricular tachyarrhythmias and 0.4% of the total cohort. HCM-related mortality was infrequent, with a rate of 0.3% per year.

“In the largest multicenter cohort of patients with HCM with ICDs, effectiveness and durability of ICDs for prevention of sudden death are demonstrated in populations from diverse countries, cultures, and healthcare systems,” Rowin told TCTMD via email. “This highlights the effectiveness of ICD in HCM, with particularly low rates of sudden death and disease-related mortality, and [shows] that the ICD initiative has favorably altered the natural history of HCM worldwide.”

He noted that there are potential risks, too, with 10% of patients having inappropriate shocks, 5% lead issues, and 2% device-related infection. That information, he said, “ultimately goes into the shared decision-making processes for implanting a device in individual patients.”

Rowin noted that most studies assessing the impact of ICDs in patients with HCM have been focused on populations from academic medical centers in the United States and Europe. He and his colleagues set out to expand the scope of the evaluation by digging into databases from 25 HCM centers across six continents—nine from Europe, eight from the US, four from Asia, and one each from Africa, Australia, Mexico, and South America.

The analysis included 3,387 patients (63% male) with HCM who had an ICD implanted between 1992 and 2024; 93% were for primary prevention and 7% secondary prevention of sudden cardiac death (SCD). Patients received their devices a median of 3.4 years after being diagnosed with HCM, at a mean age of 47 years.

Appropriate ICD shocks for ventricular tachycardia or fibrillation occurred in 2.6% of patients per year. The median time to first appropriate device activation was 4 years in the primary prevention population and 2.7 years in the secondary prevention population.

Of note, 16% of primary prevention patients received an appropriate shock 10 years or more after implantation of the device, and nearly half (47%) required multiple shocks over time.

Both findings were surprising, Rowin said. “When thinking about implanting primary prevention ICDs, we tend to think about risk over the next several years,” he said. “But these data show that interventions not uncommonly occur after more prolonged periods . . ., so when thinking about primary prevention ICDs for patients with HCM, it is really about lifelong prevention of sudden death.”

Independent predictors of appropriate ICD therapy included unexplained syncope, LV apical aneurysm, LV systolic dysfunction, a history of atrial fibrillation (AF), and nonsustained ventricular tachycardia on ambulatory monitoring in the primary prevention population, with a lower likelihood of ICD discharge among those with previous myectomy.

Through follow-up, the rate of all-cause survival was 94% in the primary prevention group and 88% in the secondary prevention group, with annual death rates of 0.8% and 1.4%, respectively (P = 0.02).

Survival free from HCM-related mortality was 97.1% at 10 years and 90.7% at 20 years in the primary prevention group and 91.3% and 75.0%, respectively, in the secondary prevention group.

Among those with primary prevention ICDs, patients from the US had a lower rate of appropriate ICD discharge versus those from other parts of the world (1.8% vs 2.1% per year; P = 0.04), along with lower rates of all-cause death (0.6% vs 1.1% per year) and HCM-related death (0.2% vs 0.5% per year; P < 0.001 for both).

“It is notable that long-term survival after an appropriate intervention was highly favorable, with 90% all-cause survival at 10 years even after an appropriate ICD shock,” Rowin said. “This is different from other forms of cardiomyopathies where mortality is high after an appropriate ICD shock often due to heart failure. This is an important principle that needs to be taken into account when considering ICD selection in HCM, in which survival with an ICD is excellent (ie, [you’re] not trading sudden death for heart failure death).”

Moving forward, the field should continue to search for ways to better select which patients are likely to receive appropriate ICD shocks.

“We need to continue to work to ensure that we identify all patients at risk for sudden death and in need of an ICD, while also identifying those patients who would not benefit from a device,” Rowin said.