Systolic time intervals in atrial fibrillation and mitral stenosis.

The duration of left ventricular ejection was related to the preceding RR interval in 15 patients with varying duration of diastole, and hence ventricularfilling time, from atrialfibrillation. Eleven had varying degrees of mitral stenosis. Left ventricular ejection time lengthened in relation to increasing RR intervals, but reached a duration beyond which no further significant increase in ejection time occurred despite a further increase in the RR interval. The RR interval needed to achieve maximum left ventricular ejection and the slope of the curve at short cycle lengths could be related to the presence and severity ofmitral stenosis as measured by echocardiography. The pre-ejection period decreased with increasing RR interval in 9 patients in whom it was measured. The ratio of pre-ejection to left ventricular ejection period decreased rapidly with increasing RR interval to reach a minimum value beyond whichfurther increase in RR intervalproduced no significant change.