LOW INCIDENCE OF VENTRICULAR ARRHYTHMIAS INDUCED BY ISCHEMIA AT THE BORDERS OF A CHRONIC INFARCT IN A MODEL WITH LOCAL POSTINFARCTION DENERVATION

Objective: The aim was to assess the arrhythmogenic potential of acute ischaemia superimposed at the borders of a chronic myocardial infarct and to analyse the effects of myocardial necrosis on local autonomic innervation in pigs. Methods: Ventricular arrhythmias were measured in alpha chloralose (100 mg.kg(-1)) anaesthetised open chest pigs during 60 min occlusion of the left anterior descending coronary artery 2 cm above the first diagonal branch (group I, n = 11) or just below this branch (group II, n = 12). These arrhythmias were compared with those induced in pigs with a one month old anteroseptal infarction (coronary ligature as in group II) submitted to a second occlusion 2 cm above the first (group III, n = 12). The area at risk after high or low ligature was measured in 12 control pigs using fluorescein. Sympathetic and parasympathetic innervation of the anteroseptal myocardium was studied in three pigs with a chronic anteroseptal infarction and in six pigs without infarction using adrenergic histofluorescence and acetylcholinesterase reaction. Results: Compared with ischaemia alone, ischaemia at the borders of a chronic infarct induced a lower incidence of ventricular fibrillation (1/12 pigs v 11/11 in group I, p < 0.001, or 6/12 in group II, p < 0.05) and a tendency towards a lower occurrence of ventricular tachycardia (2/12 pigs v 8/11 in group I, p = 0.01, and 4/12 in group II) and fewer ventricular premature beats (mean number: 105 in group I v 30 in group III, p < 0.05). The mass of the ischaemic regions after low or high occlusion was 13.3(SD 3.0) g and 23.2(5.8) g, respectively. Adrenergic and cholinergic denervation was observed inside the necrotic area, along the subendocardium surviving the necrosis, and in a band of normal bordering myocardium [width: 3.2(2.0) mm for adrenergic and 2.1(1.2) mm for cholinergic denervation]. Conclusions: Acute ischaemia at the borders of a chronic anteroseptal infarct has a low arrhythmogenic potential in pigs. In this model the peri-infarction zone shows a band of sympathetic and parasympathetic denervation secondary to the necrosis.