Intra- and interobserver variations in the measurement of systolic time intervals.

Intra- and interobserver variations in the measurement of systolic time intervals (STIs) by three experienced cardiologists were investigated in 20 tracings on which phonocardiograms, carotid pulse and electrocardiograms were recorded simultaneously. The STIs studied were the time interval from the Q wave to the aortic component of the second heart sound (Q-S2), the left ventricular ejection time (ET), the pre-ejection period (PEP), and PEP/ET. It can be concluded that (1) the present interobserver variations in the measurement of STIs were too great to be negligible and could give rise to serious problems in group or cooperative studies, and (2) the intraobserver variations may be virtually negligible in most clinical situations, although there could be some potential risk of erroneous diagnosis.