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Exercise Echocardiography in Asymptomatic or Minimally Symptomatic HCM: Exercise Capacity, and Not Rest or Exercise LV Outflow Tract Gradients Predicts Long-Term Outcomes
Study Questions:
What are the predictors of long-term outcome in asymptomatic or minimally symptomatic patients with hypertrophic cardiomyopathy (HCM) who underwent exercise echocardiography, without invasive therapies for relief of left ventricular outflow tract (LVOT) obstruction?
Methods:
The study cohort was 426 patients (44 ± 14 years; 78% men) with HCM referred for exercise echocardiography, excluding hypertensive heart disease of elderly, ejection fraction <50%, and those who underwent invasive therapy (myectomy or alcohol ablation) during follow-up. Clinical, echocardiographic (LV thickness, LVOT gradient, and mitral regurgitation [MR]), and exercise variables (percentage of age-sex predicted metabolic equivalents [METs] and heart rate recovery [HRR] at 1 minute post-exercise) were recorded. The composite endpoint was death, appropriate internal defibrillator discharge, or admission for congestive heart failure.
Results:
Patients were asymptomatic or minimally symptomatic on history, but 82% patients achieved <100% of age-sex predicted METs, and 43% had ≥2+ post-stress MR. The mean LV septal thickness, post-exercise LVOT gradient, and HRR were 2.0 ± 0.5 cm, 62 ± 47 mm Hg, 17.3 ± 2, and 31 ± 14 bpm, respectively. During a mean follow-up of 8.7 ± 3 years, there were 52 events (12%). Patients achieving >100% of age-sex predicted METs had 1% event rate versus 12% in those achieving <85%. On stepwise multivariate survival analysis, percentage of age-sex predicted METs (hazard ratio [HR], 0.76; 95% confidence interval [CI], 0.64-0.90), abnormal HRR (HR, 0.89; 95% CI, 0.82-0.97), and atrial fibrillation (HR, 2.73; 95% CI, 1.30-5.74) (all, p < 0.01) independently predicted outcomes.
Conclusions:
Patients were asymptomatic or minimally symptomatic on history, but 82% patients achieved <100% of age-sex predicted METs, and 43% had ≥2+ post-stress MR. The mean LV septal thickness, post-exercise LVOT gradient, and HRR were 2.0 ± 0.5 cm, 62 ± 47 mm Hg, 17.3 ± 2, and 31 ± 14 bpm, respectively. During a mean follow-up of 8.7 ± 3 years, there were 52 events (12%). Patients achieving >100% of age-sex predicted METs had 1% event rate versus 12% in those achieving <85%. On stepwise multivariate survival analysis, percentage of age-sex predicted METs (hazard ratio [HR], 0.76; 95% confidence interval [CI], 0.64-0.90), abnormal HRR (HR, 0.89; 95% CI, 0.82-0.97), and atrial fibrillation (HR, 2.73; 95% CI, 1.30-5.74) (all, p < 0.01) independently predicted outcomes.
Perspective:
Exercise testing is used among active patients with HCM to evaluate inducible LV outflow gradient. This study suggests that, among patients in whom no intervention is performed, clinical outcomes of death, implantable cardioverter-defibrillator discharge, or hospitalization for heart failure are best predicted by exercise capacity, but not outflow gradient. It could be assumed that patients with substantial LV outflow gradient might have been selectively referred for myectomy or septal ablation and therefore not part of this study group, introducing one possible explanation for the lack of predictive power of the degree of outflow obstruction. However, the conclusion seems sound that the ability to achieve an age- and sex-appropriate workload on functional testing is associated with a good prognosis.
Keywords: Follow-Up Studies, Mitral Valve Insufficiency, Cardiomyopathy, Hypertrophic, Heart Rate, Heart Diseases, Rest, Prognosis, Incidence, Ventricular Outflow Obstruction, Workload, Heart Failure, Survival Analysis, Defibrillators, Implantable, Echocardiography, Exercise Test
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