Dependence of temporal variability of ventricular recovery on myocardial fibrosis. Role of mechanoelectric feedback?

Abstract

The study was aimed at establishing the effect of factors involved in the expression of mechanoelectric feedback in the heart, such as R-R interval and connective tissue, on time dependent changes in ventricular recovery, as determined at the body surface by beat to beat variability of QRST integral maps (BBV-IM). We used 15 normal 6-month-old Wistar rats. In each anesthetized animal, we performed a 3-minute continuous recording of 44. The simultaneous chest ECGs. The signals were interactively processed, 1) to determine mean R-R interval and R-R variability throughout the recording period and 2) to compute QRST integral maps from approximately 50 beats belonging to the end of expiration. Then BBV-IM was calculated and expressed as percentage of beats significantly differing from a template. At sacrifice, the amount of myocardial fibrosis was morphometrically evaluated. R-R interval was 149 ms +/- 4, R-R interval variability 0.008 +/- 0.001 and BBV-IM 30.7% +/- 4.4. Myocardial fibrosis expressed as % volume of left ventricular myocardium, numerical density of fibrotic foci and average cross-sectional area of the foci was 3.0% +/- 0.4, 3.8 +/- 0.6 and 4.4 microns(2)/1000 +/- 0.1 respectively, BB-IM was positively correlated to the % volume of fibrosis (r = 0.83, P < 0.0003). Both measurements were positively correlated to R-R interval (BBV-IM: r = 0.83, P < 0.0001; % volume of fibrosis: r = 0.87, P < 0.001) and negatively correlated to cardiac weights (BBV-IM: r = -0.79, P < 0.0005; % volume of fibrosis: r = -0.75, P < 0.001). Beat to beat changes in ventricular repolarization attributable to mechanoelectric transduction can be detected at the body surface by means of BBV-IM.