Hypertrophic cardiomyopathy: non-invasive assessment of diastolic and systolic functional parameters in relation to heart rate.

Hypertrophic cardiomyopathy (HC) is characterized by reduced left ventricular compliance and subsequent filling abnormalities. To study the pathophysiologic changes in parameters of left ventricular systolic and diastolic performance as a function of increasing heart rate 14 patients with HC (32 +/- 12 yrs; 11 M, 4 F) and 4 normal individuals were subjected to equilibrium radionuclide ventriculography (99mTc-labelled red blood cells) at rest and during incremental right atrial pacing; heart rate was increased in steps of 20 beats per min from basal state to the individual symptom-limited endpoint. Mean symptom-limited heart rate was 141 +/- 28 in HC and 160 in normals (p less than .01.). At each pacing level filling and ejection parameters as well as the left ventricular endsystolic (LVESV) and enddiastolic volume (LVEDV) were determined relative to resting volumes at a heart rate of 78 +/- 8. At the individual maximal pacing rate HC revealed a decline in LVEDV to 61 +/- 4% (p less than .001) and an increase in LVESV to 117 +/- 14% (p less than .001) resulting in decreasing ejection fractions at heart rates above 120. Peak LV filling rates initially increased but subsequently decreased steeply at heart rates above 100; peak LV ejection rates in HC showed a similar pattern with increasing frequency. Time intervals to peak ejection and peak filling rate did not differ from normal. Thus, patients with HC demonstrated combined left ventricular diastolic and systolic abnormalities with increasing heart rate leading into a low-input low-output circulatory state. This probably explains not only the symptoms associated with HC, but also supports the concept of "hemodynamic syncope" in HC.