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A SINGLE 5 MINUTE PERIOD OF RAPID ATRIAL-PACING FAILS TO LIMIT INFARCT SIZE IN THE INSITU RABBIT HEART

MARBER, MS; WALKER, DM; EVESON, DJ; WALKER, JM; YELLON, DM; (1993) A SINGLE 5 MINUTE PERIOD OF RAPID ATRIAL-PACING FAILS TO LIMIT INFARCT SIZE IN THE INSITU RABBIT HEART. CARDIOVASC RES , 27 (4) 597 - 601.

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Abstract

Objective: Rapid pacing has been shown to precondition the dog heart against ischaemic dysrrhythmia. The aim of this study was to determine whether rapid pacing could also limit infarct size. Methods: Rabbits (n=5) were rapidly paced via the left atrium at 420-480 beats.min-1. Five min of rapid pacing and 10 min of recovery in sinus rhythm were followed by 45 min of regional ischaemia and 120 min of reperfusion. Control rabbits (n=9) were treated identically without prior rapid pacing. Infarct size was determined in both groups using tetrazolium and expressed as a percentage of the area at risk demarcated by fluorescent miscrospheres. In a separate series of experiments, rapidly paced Langendorff perfused rabbit hearts (n=9) were used to determine coronary flow under perfusion conditions designed to simulate the in vivo situation during rapid pacing. Results: Rapid pacing caused a fall in systolic pressure from 91.4(SEM 4.5) to 47.0(5.9) mm Hg (p<0.01) and diastolic pressure from 67.2(2.9) to 23.6(3.2) mm Hg (p<0.01). Both recovered within 30 s of cessation of pacing. During rapid pacing the action potential duration shortened from 192(13) to 128(5) ms (p=0.01) and developed electrical alternans (n=4). Following rapid pacing the ECG showed either ST depression or T wave inversion (n=4). Despite these profound changes, rapid pacing did not reduce infarct size v control [52.7(4.6)% v 60.8(9.1)% of the area at risk, respectively]. The in vitro experiments estimated that rapid pacing would result in a reduction in coronary flow to 44% of that in sinus rhythm without a significant rise in lactate efflux. Conclusions: In our model, pretreatment with rapid pacing fails to reduce infarct size. The most likely reason for this is that rapid pacing at a rate of 480 beats.min-1 does not cause myocardial ischaemia of sufficient severity to trigger the preconditioning response.

Type:Article
Title:A SINGLE 5 MINUTE PERIOD OF RAPID ATRIAL-PACING FAILS TO LIMIT INFARCT SIZE IN THE INSITU RABBIT HEART
Keywords:RAPID PACING, ISCHEMIC PRECONDITIONING, INFARCTION, ISCHEMIC MYOCARDIUM, REPERFUSION, ARRHYTHMIAS, PROTECTION, ALTERNANS
UCL classification:UCL > School of Life and Medical Sciences > Faculty of Population Health Sciences > Institute of Cardiovascular Science

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