Cardiac sympathetic nerve activity burst size increased significantly before the onset of ventricular fibrillation or tachycardia in a conscious sheep model of acute myocardial infarction (P=0.01).
An early increase in cardiac sympathetic nerve activity burst size is associated with the genesis of ventricular fibrillation or tachycardia during acute myocardial infarction in a conscious sheep model.
valor p: p=0.01
The association between cardiac sympathetic nerve activity (CSNA) and ventricular fibrillation (VF) during acute myocardial infarction (MI) has not been assessed in conscious animal models. During the first 60 min post-MI, mean blood pressure (MBP), heart rate (HR), and CSNA were recorded continuously in 20 conscious sheep. Resistant sheep (group A, n = 10) were compared with susceptible sheep (group B, n = 10) who developed fatal VF (n = 7) or sustained ventricular tachycardia (VT, n = 3). The mean time to VF/VT was 28.1 +/- 3.3 min. In group B, MBP, HR, and CSNA were averaged at each consecutive minute from baseline at 14 min before the onset of VF/VT and compared with time-matched values in group A. When compared with those of group A, indexes of CSNA burst size increased before the onset of VF/VT: burst area/minute (F(13,208) = 2.17, P = 0.01) and burst area/100 beats (F(13,208) = 1.86, P = 0.04). By contrast, burst frequency indexes were not significantly different: burst frequency (F(13,208) = 1.6, P = 0.09) and burst incidence (F(13,208) = 1.48, P = 0.13). In group A, CSNA burst area/min and burst area/100 beats did not change across this time period (F(13,117) = 0.97, P = 0.5, F(13,117) = 0.96, P = 0.7) but increased with time in group B (F(13,91) = 2.3, P = 0.01; and F(13,91) = 2.25, P = 0.01). Between-group comparisons demonstrated no differences in time of onset of ventricular ectopic beats: 18.5 (range 12-24) in group A versus 15.0 min (range 7-22) in group B (Mann-Whitney U-test, P = 0.09). Pre-MI baroreflex slopes were similar: R-R slopes were 11.8 +/- 2 and 15.6 +/- 1.1 ms/mmHg (t(18) = -1.6, P = 0.14). CSNA slopes were -1.8 +/- 0.3 and -2.3 +/- 0.2%/mmHg (t(18) = -1.4, P = 0.2). An early increase in CSNA burst size indexes (before 60 min post-MI), mediated by an excitatory sympathetic reflex, is important in the genesis of VF/VT.
Jardine et al. (Sat,) conducted a other in Acute myocardial infarction and ventricular fibrillation (n=20). Susceptibility to ventricular fibrillation/tachycardia vs. Resistance to ventricular fibrillation/tachycardia was evaluated on Cardiac sympathetic nerve activity burst size (burst area/minute and burst area/100 beats) (p=0.01). Cardiac sympathetic nerve activity burst size increased significantly before the onset of ventricular fibrillation or tachycardia in a conscious sheep model of acute myocardial infarction (P=0.01).