Isovolumic relaxation period in hypertrophic cardiomyopathy

Previous reports have demonstrated that patients with hypertrophic cardiomyopathy have a prolonged isovolumic relaxation period as a result of a delay in mitral valve opening, reflecting a reduced rate of fall of left ventricular pressure. This period as measured from the aortic closure sound (A2 on phonocardiogram) to the opening of the mitral valve (on echocardiogram) was determined in 84 patients with hypertrophic cardiomyopathy and compared with findings in 31 normal volunteers. The duration of the isovolumic relaxation period in the 84 patients had a wide range from 0 to 160 ms (mean 71 +/- 32) that was not significantly different from that in normal subjects (63 +/- 11 ms). However, it was possible to identify a group of 15 patients with an extremely short isovolumic relaxation period, 2 standard deviations below the normal range. This shortening was due to a marked delay in aortic closure sound (A2) due to late left ventricular-aortic pressure crossover, as well as early opening of the mitral valve secondary to elevated left atrial pressure, which was confirmed by hemodynamic correlations and digitized echocardiographic data. In this subset of patients, A2 is a poor marker of the onset of rapid left ventricular pressure decline and, thus, the interval from A2 to mitral valve opening is not a valid reflection of left ventricular relaxation. It is concluded that in hypertrophic cardiomyopathy, both the timing and sequence of relaxation are abnormal, as is the rate of relaxation. Furthermore, the isovolumic relaxation period is multifactorially determined and depends not only on the rate of left ventricular pressure decline, but also on the magnitude of the pressure drop from A2 to mitral valve opening. All of these determinants must be kept in mind when the isovolumic relaxation period is used as a measure of left ventricular relaxation.