Effects of postextrasystolic potentiation on systolic time intervals

Abstract

The changes in systolic time intervals associated with postextrasystolic potentiation were studied in 48 patients whose left ventricular function was categorized angiographlcally into four groups—normal function (I) and mlld (II), moderate (III) and severe (IV) left ventricular dysfunction. Postectopic potentiation in all groups caused a decrease in preejection period/left ventricular ejection time (PEP/LVET) ratio. The greatest potentiation and decreases in PEP/LVET ratio were noted in beats where the difference in compensatory pause and coupling interval (both expressed as percent of basic cycle length [CP percent — CI percent]) exceeded 40. The decrease in the ratio was least in the normal subjects (Group I) and maximal in Group IV patients. The pattern of response of the rate-corrected left ventricular ejection time and preejectlon period was also different at the four levels of ventricular function. Marked shortening of ejection time with minimal shortening of preejection period occurred in Group I, but in Group IV patients there was marked shortening of preejection period and minimal shortening of ejection time. An intermediate response was seen in Group II and III patients. The amount of shortening of ejection time exceeded that of preejection period in Group II patients; the reverse was true in Group III patients. The group responses differed with a significance of 2 P <0.001 except when Group II was compared with Group III, when the significance was 2 P <0.025. Thus, measurement of changes in systolic time intervals associated with postextrasystolic potentiation is of value as a noninvasive means of assessing resting left ventricular function.