Utility of echophonocardiographic timing intervals for the prediction of left ventricular filling pressures

Recent evidence has suggested that the left ventricular (LV) filling pressure can be estimated from echophonocardiographic recordings of the aortic component of the 2nd heart sound and the mitral valve echogram. The ratio of the Q wave to the closure point of the mitral valve (QC) and the time interval from the A2 to the E point of the mitral valve (A2E) have been demonstrated to increase with increasing LV filling pressures. However, with active coronary ischemia, the isovolumic relaxation period becomes prolonged which may prolong the A2E interval. In this study we systematically evaluated the QC and A2E intervals using a canine model of acute LV dysfunction associated with elevation of LV filling pressures. Coronary artery microsphere embolization was used to induce global LV dysfunction and ischemia. Acute LV dysfunction did not alter the QC interval, but lengthened the A2E interval (baseline 94 ± 31 ms, severe LV dysfunction 128 ± 27 ms; p < 0.01). The QC/A2E ratio shortened with LV dysfunction (baseline 0.43 ± 0.19, severe LV dysfunction 0.32 ± 13; p < 0.01). No significant relation was noted between the QC/A2E ratio and the LV end-diastolic or minimal pressure. To further alter LV filling pressures, nitroglycerin and nitroprusside were used to reduce the LV end-diastolic pressure to < 15 mm Hg. The QC interval was unchanged with either agent. The A2E interval shortened, while the time constant of relaxation and the isovolumic relaxation period also shortened. We conclude that the QC/A2E ratio is not useful in predicting the LV filling pressures. Furthermore, alterations in the A2E interval reflect alterations in LV relaxation.