Identification of High- Risk Hypertrophic Cardiomyopathy Patients
ABSTRACT & COMMENTARY
Synopsis: An abnormal blood pressure response identifies a higher risk group, but the low positive predictive accuracy indicates that further risk stratification is necessary in this group.
Source: Sadoul N, et al. Circulation 1997;96: 2987-2991.
Identification of hypertrophic cardiomyopathy (HCM) patients at risk for sudden cardiac death (SCD) is important to plan appropriate interventions. Thus, Sadoul and associates at St. George’s Hospital in London prospectively evaluated the prognostic value of the blood pressure responses during exercise in 161 consecutive patients aged 8-40 years (mean, 27) with HCM and not on cardiac drugs. Only patients with a history of nonfatal cardiac arrest were excluded. Maximum Bruce protocol treadmill exercise testing showed a normal blood pressure response in 63% of the patients (rising 20 mmHg with no fall ³ 20 mmHg during exercise) and an abnormal response in 37% of the patients. There were no differences in clinical characteristics between those with and without a normal blood pressure response. During the mean 44-month follow-up, 40 patients were on beta or calcium blockers, and, of those, 31 were on amiodarone, two received an ICD, two had myectomy, and eight had dual-chamber pacemakers implanted. SCD occurred in 12 patients3% in the normal blood pressure response group and 15% in the abnormal group (P < 0.005; OR, 3.0). Abnormal response had a sensitivity of 75%, a specificity of 66%, a negative predictive value of 97%, and a positive predictive value of 15% for predicting SCD. Other previously established risk factors such as syncope, family history of SCD, and non-sustained VT on Holter were not predictive of SCD. Sadoul et al conclude that an abnormal blood pressure response identifies a higher risk group, but the low positive predictive accuracy indicates that further risk stratification is necessary in this group.
COMMENT BY MICHAEL H. CRAWFORD, MD
SCD is a serious problem in young patients with HCM because it may be the first manifestation of the disease in about half. Previous epidemiologic studies have identified a history of syncope and a family history of HCM with SCD as specific markers for SCD, but they have a low positive predictive accuracy. Exercise hypotension has been observed in about one-third of young patients with HCM, and it is associated with a family history of SCD. Hemodynamic studies have shown that it is due to an exaggerated fall in peripheral resistance during exercise and is associated with a general abnormality in vasomotor control. This prospective study has established that it is a potent risk factor for SCD, but, like the others mentioned above, it is most valuable when negative.
In older patients, non-sustained ventricular tachycardia on Holter monitoring has been the most useful predictor of SCD but is also most useful when negative (predictive value, 97%) rather than positive (predictive value, 20-25%). The detection of septal ischemia by exercise thallium perfusion scanning has been found useful by some investigators but not by the London group. Eventually, a certain genetic pattern may be the best predictor of clinical outcome, but the complexity of the genetic picture makes this approach impractical at this time. Thus, we are left with using the clinical picture to predict future events. Clearly, in the young HCM patient, exercise hypotension is an important finding. However, there is currently no definitive treatment for this vasomotor instability that has been shown to reduce mortality. Nevertheless, the identification of high-risk patients may be of value, since fortuitous Holter studies have shown arrhythmias during SCD episodes that may be suppressible with antiarrhythmic drugs or terminated with an ICD. Interestingly, only one of the 12 patients with SCD in this study was on amiodarone.
Sudden death in young hypertrophic cardiomyopathy patients is strongly predicted by:
a. resting LV outflow gradient.
b. bifid arterial pulse.
c. exercise-induced hypotension.
d. prolonged QRS on ECG.
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