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Syncope and Hypertrophic Cardiomyopathy
Abstract & commentary
By John P. DiMarco, MD, PhD, Professor of Medicine, Division of Cardiology, University of Virginia, Charlottesville. Dr. DiMarco is a consultant for Novartis and does research for Medtronic and Guidant.
Source: Spirito P, et al. Syncope and risk of sudden death in hypertrophic cardiomyopathy. Circulation. 2009;119: 1703-1710.
Syncope is commonly accepted to be a danger sign in patients with hypertrophic cardiomyopathy (HCM). In this paper, Spirito et al report data from a registry of 1,511 patients with HCM who have been followed longitudinally at four institutions. The diagnosis of HCM was based on standard echocardiographic criteria. The data available in the registry included: age, gender, family history of sudden death, NYHA functional class, degree of left ventricular (LV) outflow tract obstruction, LV wall thickness, left atrial dimension, and treatment. Syncope was defined as a sudden and brief loss of consciousness associated with loss of postural tone with spontaneous recovery. Based on clinical data, episodes of syncope were classed as either "neurally mediated" or "unexplained."
At the time of their initial evaluation, 207 patients had a prior history of syncope. In 153 patients, the syncope was classified as "unexplained," with 118 in this group reporting syncope at rest and 35 during intense exertion. Fifty-two patients reported syncope with features suggesting a neurally mediated origin. The remaining 1,306 patients did not have a history of syncope when they initially presented. There were few clinically significant differences between the groups. Overall, the mean age was 46 ± 20 years. The entire group was 61% male. A family history of sudden death was reported by 19% of the patients, and 11% of the patients were New York Heart Association functional class III or IV. Only 7% had left ventricular wall thickness greater than 30 mm. At the time of the initial evaluation, 41% of the patients were receiving beta blockers, 25% calcium antagonists, 6% amiodarone, and 12% diuretics. During a follow-up period of 5.6 ± 5.2 years, there were 240 deaths (14% of the entire group). Of these deaths, 74 were classified as sudden and presumed cardiac, 54 were caused by heart failure, 26 were stroke-related, and 60 were due to noncardiac causes. For those patients who died suddenly, the mean age was 42 ± 18 years. Among the 1,511 study patients, there were 98 (6%) who received an ICD after initial evaluation. Of these 98 ICD recipients, five patients received one or more appropriate ICD therapies. Prior syncope, if unexplained, could be related to risk for sudden death. For the 153 patients with a history of unexplained syncope, the relative risk for sudden death was 1.78. There was, however, no relationship between neurally mediated syncope and sudden death (relative risk 0.91). Recurrent episodes of syncope, reported by 63 patients, did not increase the risk for sudden death. For these patients, the relative risk was 1.26. Unexplained syncope was more ominous in patients under 18 years of age. In this age group, the hazard ratio was 8.0. The time interval between unexplained syncope and the risk of sudden death was also examined. Patients with a recent (within six months) episode of unexplained syncope had a five-fold increased risk for sudden death compared to patients without recent syncope. Patients with only remote episodes of syncope (greater than five years previously) had no increased risk of sudden death (hazard ratio 0.38). Finally, Spirito et al examined the interaction between age, syncope, and sudden death. There were 147 patients who were under 18 years of age at study entry. During 6.5 ± 5.7 years of follow-up, 15 (10%) of these patients died suddenly. The sudden death incidence in this group was 15.7 per 1,000 person years.
Spirito et al concluded that unexplained syncope, particularly if it is recent and if it occurs before age 18, is a major risk factor for sudden death in patients with HCM.
Sudden death is the most dreaded complication of HCM. Prior reports have described risk factors for sudden death in these patients. Commonly cited risk factors include a history of syncope, spontaneous non-sustained ventricular arrhythmias, hypotension with exercise, a positive family history of sudden death at a young age, and massive left ventricular hypertrophy. Any one of these risk factors is considered a possible indication for ICD implantation for primary prevent of sudden death. This paper further clarifies the prognostic significance of syncope. Syncope with the classic features of a neurally mediated event is not associated with increased risk. A remote episode of syncope with no recurrence for several years also should not be considered a risk factor. Recent "unexplained" syncope, however, is more worrisome and, particularly in younger patients, may be the deciding factors toward proceeding with an ICD.