Response to isoproterenol as a prognostic indicator of evolution from hypertrophic cardiomyopathy to a phase resembling dilated cardiomyopathy

Objectives. We sought to assess whether isoproterenol stress echocardiography could detect in advance in which patients hypertrophic cardiomyopathy mould progress to a phase resembling dilated cardiomyopathy. Background. In a few patients, hypertrophic cardiomyopathy has been reported to progress to a phase characterized by systolic dysfunction and left ventricular dilation, resembling dilated cardiomyopathy. Methods. Echocardiograms were recorded before and immediately after intravenous infusion of isoproterenol (0.02 mu g/kg body weight per min) for 5 min in 18 patients with typical hypertrophic cardiomyopathy (i.e., hypertrophied, hyperdynamic and nondilated) to determine the difference in fractional shortening, The patients were categorized into those with a good response (difference in fractional shortening >7%, 14 patients) and those with a poor response (difference less than or equal to 7%, 4 patients). Changes in left ventricular end-diastolic diameter and fractional shortening were evaluated by using serial echocardiography over an average follow-up period of 5.4 years. Results. In the good response group, neither end-diastolic diameter nor fractional shortening changed significantly during the follow-up period. In the poor response group, end-diastolic diameter significantly increased from a mean +/- SD of 41 +/- 5 to 53 +/- 5 mm (p < 0.05), and fractional shortening significantly decreased from 40 +/- 12% to 29 +/- 10% (p < 0.05), All patients in the poor response group showed a substantial decrease (greater than or equal to 5%) in fractional shortening and an increase (greater than or equal to 5 mm) in end-diastolic diameter. One patient developed congestive heart failure due to systolic dysfunction during the observation period. Conclusions. The present study confirmed that impaired responses to isoproterenol infusion are related to future deterioration of left ventricular performance in patients with typical hypertrophic cardiomyopathy.