186 EFFECT OF ATRIAL PACING ON ECHO-DERIVED LEFT VENTRICULAR DIMENSIONS IN CHILDREN

Abstract

The effects of atrial pacing on M-mode echocardiographic (ME) estimates of left ventricular (LV) dimensions were studied in 19 children during cardiac catheterization. Pacing was in increments of 20 beats/minute up to 160 bpm maximum. Over wide range of heart rate (HR), LV dimensions at Q wave and at peak of R wave were similar for end-diastolic diameter (LVEDD) (r = .99) or wall thickness (WT) (r = .98). LV measurements were related to HR by regression analysis. With increasing HR up to 140 bpm, LVEDD diminished (r = −.77) (from resting HR to 120 bpm, P < .005); from 120 bpm to 140 bpm, P < .001; from 140 bpm to 160 bpm, P = NS). However, LV end-systolic diameter (LVESD) correlated poorly with HR (r = −.35). Because of greater reduction in LVEDD than in LVESD, minor axis shortening decreased with HR (r = −.60). Estimated LV mass did not change significantly; however, WT/LVEDD or mass/volume ratio increased with HR (r = .48). LV diameters obtained sequentially at 20 msec intervals were analyzed for dD/dt during systole (dD/dt - s) and during diastole (dD/dt - d). From resting HR to 120 bpm pacing, borderline reduction of peak dD/dt - s was observed (P < .05); by contrast, significant increase of peak dD/dt - d occurred (P < .005) suggesting greater sensitivity of ventricular filling to HR change. ME-derived LV size/function in children must be interpreted taking into consideration not only age and body size but HR as well.

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