Cardiomyopathy
Utility of cardiopulmonary exercise in the assessment of clinical determinants of functional capacity in hypertrophic cardiomyopathy

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Abstract

The utility of metabolic gas exchange measurements in evaluating the severity and determinants of exercise limitation was studied during upright symptom-limited cardiopulmonary exercise in 135 consecutive patients with hypertrophic cardiomyopathy (HC) and 50 healthy age- and gender-matched volunteers. Peak oxygen consumption (VO2) was less than predicted (age, gender, and size) in 99% patients. Peak VO2 was significantly associated with New York Heart Association functional class; however, there was considerable overlap of peak VO2 between classes I and III (70 ± 15%, 56 ± 15%, 35 ± 11%, respectively). Patients with abnormal blood pressure responses and patients with chronotropic incompetence during exercise had lower percent-predicted peak VO2 than patients with normal blood pressure and heart rate responses during exercise (p = 0.0001 and p <0.001, respectively). Percent-predicted peak VO2 was similar in patients with and without resting left ventricular outflow obstruction. Of those patients with resting gradients, however, there was a strong inverse correlation between the magnitude of the gradient and peak VO2 (r = 0.5; p <0.001). In conclusion, peak VO2 is significantly related to New York Heart Association functional class in this group of patients with HC, but peak VO2 is a superior measure of cardiovascular performance in individual patients. Our peak VO2 data indicate that mechanical obstruction has an adverse pathophysiologic effect on functional capacity and provide the rationale to support treatments aimed at gradient reduction. Low peak VO2 characteristics including those with normal or near-normal left ventricular wall thickness suggests that measurement of peak VO2 may aid in the differential diagnosis between HC and athlete’s heart.

Section snippets

Patient characteristics

Between January 1997 and March 1998, 135 consecutive patients with HC underwent cardiopulmonary exercise testing. Clinical characteristics of the patients are listed in Table I. The diagnosis of HC was based on the conventional World Health Organization definition6 in 109 patients (81%). The remaining patients fulfilled recently proposed criteria for HC within the context of familial disease or were proved gene carriers.7, 8

Controls

Fifty healthy age- and sex-matched sedentary volunteers with normal

Echocardiography

The results of left ventricular wall thickness measurements, patterns of left ventricular hypertrophy, mean Wigle score, and left ventricular inflow and outflow velocities are presented in Table I. The mean E-wave velocity was 0.7 ± 0.2 m/s (range 0.2 to 1.8). The mean A-wave velocity was 0.6 ± 0.3 m/s (range 0.2 to 1.4). The mean E/A ratio was 1.5 ± 0.8 (range 0.4 to 6.0). Twenty-one patients (16%) had an E/A ratio of <1.

Exercise

All exercise tests were completed without adverse complications. One

Cardiopulmonary parameters in relation to symptoms

This study demonstrated that the peak VO2 was low in almost all patients with HC irrespective of symptomatic status, magnitude of left ventricular wall thickness, presence or absence of a left ventricular outflow gradient, or exercise-related heart rate and blood pressure responses. Patients in New York Heart Association class I had higher cardiopulmonary indexes (except ΔVE/ΔVCO2) than those in classes II and III, but there was considerable variation in the distribution of these indexes in

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    Dr. Sharma is supported by a fellowship grant from the British Heart Foundation, London, United Kingdom.

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