Abstract & Commentary
Comments by John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is on the Editorial Board of Clinical Cardiology Alert.
Synopsis: Patients with HCM exhibit a high frequency of ventricular and supraventricular arrhythmias during ambulatory ECG monitoring, but sudden death is uncommon and not predicted by arrhythmias.
Source: Adabag AS, et al. Spectrum and Prognostic Significance of Arrhythmias on Ambulatory Holter Electrocardiogram in Hypertrophic Cardiomyopathy. J Am Coll Cardiol. 2005;45:697-704.
In this paper, Adabag and colleagues describe the prevalence and prognostic significance of arrhythmias detected by ambulatory ECG monitoring in patients with hypertrophic cardiomyopathy (HCM). In order to exclude tertiary referral patients who might not be representative of all patients with HCM, Adabag et al selected from their clinic patients, those who lived in the region around their center in Minneapolis. Patients who were referred for tertiary care from other centers were excluded. Of the 296 HCM patients that were identified, 178 were identified as having at least one 24-hour ambulatory ECG recording. These patients ranged in age from 5 to 89 years (mean 50 ± 18 years) and 57% were male. Almost half (48%) were in New York Heart Association (NYHA) functional class I, but 34% were in class II and 18% were in classes III or IV. Patients could have either an obstructive or a nonobstructive form of HCM. Thirty-nine (22%) patients had a left ventricular outflow gradient greater than or equal to 30 mm/Hg at baseline. Follow-up from the time of the ambulatory ECG recording to last contact ranged from 1 to 22 years (mean 5.5 ± 3.4 years). Cardiac medications were prescribed based on the patients’ symptoms. At the time of the ambulatory ECG recording, 79 patients were receiving beta adrenergic receptor blockers, 52 verapamil, 7 disopyramide, and 4 amiodarone. Twenty patients in the group had an implantable cardioverter defibrillator during the course of the study.
Ventricular arrhythmias on ambulatory ECG were very common in the study. During the 24-hour period of recording, 88% of the patients had greater than or equal to 1 PVC, with 40 having greater than 200 PVCs/24 hours, and 21 greater than or equal to 500 PVCs. Seventy-four (42%) had couplets. Fifty-six (31%) had runs of nonsustained ventricular tachycardia (NSVT). Of these, 18 had > 3 runs and 12 > 5 runs within the 24-hour period. The bursts of NSVT ranged from 3 to 26 beats per minute, at an average rate of 150 bpm. NSVT occurred more commonly in patients with advanced symptoms (NYHA classes III or IV), and was usually asymptomatic. Symptoms related to NSVT were reported by only 2 of the 56 patients. There was no relationship between the use of cardioactive drugs and the presence of arrhythmias.
In addition to the ventricular arrhythmias described above, 67 (38%) patients had runs of a supraventricular arrhythmia. Most of these were short runs of atrial tachycardia. Atrial fibrillation was detected in 16 (9%) of the patients, and was more common in older patients with an enlarged left atria and in those with advanced symptoms. Sinus bradycardia, defined as an average heart rate less than 60 bpm in over 24 hours, was seen in 25 (14%) patients. In addition, 31 (17%) had first degree atrioventricular block, 6 (3%) had second degree AV block, and 12 (7%) had sinus pauses of greater than two seconds duration. The severity of left ventricular hypertrophy was associated with an increased prevalence of NSVT, but a reversed pattern was seen for supraventricular arrhythmias.
During follow-up, 15 (8%) of 178 patients died of HCM related causes. This included 11 sudden deaths and 4 heart failure or stroke deaths. An additional 6 patients died of coronary artery disease, and 16 died of noncardiac or unknown causes. HCM-related sudden death occurred at a rate of 1.1% per year. The estimated rate for sudden death was 1.8 per year in patients with NSVT on their ambulatory ECG vs 0.8% per year in those without nonsustained VT. This difference did not achieve statistical significance. Predictive values, sensitivity and specificity of ventricular arrhythmias on Holter, showed low positive predictive value but a high negative predictive value.
Adabag et al conclude that in selected patients with HCM, some exhibit a high frequency of ventricular and supraventricular arrhythmias during ambulatory ECG monitoring. In such a population, however, sudden death is uncommon, and the detection of even complex arrhythmias has a low positive predictive value.
Comments
Sudden death is one of the most feared complications of patients with hypertrophic cardiomyopathy. Sudden death may occur both in relatively asymptomatic individuals and in those with advanced heart failure. Ambulatory ECG monitoring has been proposed as a way to risk stratify individuals and select those who might benefit from specific therapy to prevent sudden death. Unfortunately, studies with antiarrhythmic drugs, beta blockers, and calcium channel blockers have not been shown to be effective for sudden death prevention in patients with HCM. In studies performed in tertiary centers specializing in the management of HCM patients, the detection of nonsustained VT on an ambulatory monitor has been thought to be a useful risk factor for predicting sudden death. Other risk factors have included malignant family histories, severe left ventricular hypertrophy (greater than or equal to 30 mm in wall thickness), and a history of syncope. Patients studied in tertiary care centers, however, might not represent the general population of patients with HCM. This study shows that, although ventricular and supraventricular arrhythmias are almost ubiquitous in patients with HCM, their prognostic significance in an individual is limited, since the sudden death rate in such a cohort is quite low.
The genetics of HCM are quite complicated. Some kindreds appear to have an unusually high risk for sudden death, while others seem to be in little danger. Hopefully, as we learn more about the nature of the disease, we will be better able to characterize patients who need specific and early interventions to prevent sudden death. The ambulatory ECG does not appear to be as helpful for risk stratification as was previously thought.
Patients with HCM exhibit a high frequency of ventricular and supraventricular arrhythmias during ambulatory ECG monitoring, but sudden death is uncommon and not predicted by arrhythmias.
You have reached your article limit for the month. Subscribe now to access this article plus other member-only content.
- Award-winning Medical Content
- Latest Advances & Development in Medicine
- Unbiased Content