Pacing-induced dyssynchrony during early reperfusion reduces infarct size.

OBJECTIVES: Considering the recent discovery of postconditioning, we investigated whether intermittent dyssynchrony immediately upon reperfusion induces cardioprotection as well. BACKGROUND: Intermittent dyssynchrony, induced by ventricular pacing, preconditions myocardium. METHODS: Isolated ejecting rabbit hearts were subjected to 30-min coronary occlusion and 2-h reperfusion. Control, left ventricular (LV) pacing preconditioning (LVPpreC) (3 x 5-min LV pacing), and LV pacing postconditioning (LVPpostC) (10 x 30-s LV pacing during early reperfusion) groups were studied. Mechanical effects of LV pacing were determined using local pressure-length loops (sonomicrometry), whereas effects on myocardial lactate release and coronary flow were assessed from coronary effluent and fluorescent microspheres, respectively. Anesthetized pigs underwent 60-min coronary occlusion and 3-h reperfusion in control and right ventricular (RV) pacing postconditioning groups (RVPpostC) (10 x 30-s RV pacing during early reperfusion). In all hearts, area at risk and infarct size were determined with blue dye and triphenyltetrazolium chloride staining, respectively. RESULTS: Infarct size, normalized to area at risk, was 47.0 +/- 12.3% in control rabbit hearts, but significantly smaller in LVPpreC (17.8 +/- 6.4%) and LVPpostC hearts (17.9 +/- 4.4%). Left ventricular pacing significantly altered regional mechanical work, but did not affect coronary flow or lactate release. In pigs, infarct size was significantly smaller in RVPpostC (9.8 +/- 3.0%) than in control (20.6 +/- 2.2%) animals. CONCLUSIONS: Intermittent dyssynchrony during early reperfusion reduces infarct size in 2 different animal models. Dyssynchrony-induced postconditioning cannot be attributed to graded reperfusion but may be induced by modulation of local myocardial workload. Dyssynchrony-induced postconditioning opens new possibilities for cardioprotection in the clinical setting.

Pacing-induced dys-synchrony preconditions rabbit myocardium against ischemia/reperfusion injury.

BACKGROUND: Because increased mechanical load induces preconditioning (PC) and dys-synchrony increases loading in late-activated regions, we investigated whether dys-synchrony induced by ventricular pacing (VP) at normal heart rate leads to cardioprotection. METHODS AND RESULTS: Isolated working rabbit hearts were subjected to 35 minutes of global ischemia and 2 hours of reperfusion. Seven hearts underwent VP PC (3 periods of 5 minutes VP at the posterior left ventricular [LV] wall), 7 hearts underwent ischemic preconditioning (IPC) (3 periods of 5 minutes of global ischemia), and 9 hearts served as control (C). LV pressure and sonomicrometry were used to assess global hemodynamics and segment work (SW) and end-diastolic segment length (EDSL) in anterior and posterior LV myocardium. Myocardial release of lactate and expression of proBNP mRNA were determined to gain insight in molecular processes involved in VP PC (*P<0.05). Infarct size (triphenyl tetrazolium chloride staining) was 18.3+/-13.0% in group C, and was uniformly reduced in the VP PC and IPC groups (1.8+/-0.8%*, and 3.5+/-3.1%*, respectively; and not significant between VP PC and IPC). LV posterior wall pacing (VP PC group) increased EDSL (by 6.3+/-5.8%*) and SW (to 335+/-207%*) in the LV anterior wall, whereas posterior wall SW decreased to negative values (-23+/-63%*). LV pacing did not significantly change lactate release and coronary flow but significantly increased proBNP mRNA expression in both anterior and posterior myocardium as compared with controls. CONCLUSIONS: Intermittent dys-synchrony is equally cardioprotective as "classical" IPC. Stretch-mediated signaling is a more likely trigger for VP PC than ischemia. VP PC is potentially applicable in cardiac surgery.