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Effect of pre-existing four hour coronary stenosis on ventricular arrhythmias during a subsequent 10 minute occlusion in dogs.

STUDY OBJECTIVES
The aim was to assess the effect of pre-existing coronary stenosis on ventricular arrhythmia during subsequent acute coronary occlusion.


DESIGN
Dogs with a 4 h intact interval followed by a 10 min occlusion of left anterior descending coronary artery (group A) were compared for ventricular arrhythmias with dogs with a 4 h stenosis of the same artery followed by a 10 min occlusion (group B). Myocardial blood flow was measured in the ischaemic myocardium using the H2 gas clearance method to exclude dogs with good collateral flow (myocardial blood flow greater than 11.0 ml.min-1.100g-1).


EXPERIMENTAL ANIMALS
35 mongrel dogs of either sex, weight range 11-26 kg, were used in the experiments (group A, n = 17; group B, n = 18). After exclusion of dogs with good collateral circulation there were 11 dogs in group A (subgroup A1) and 12 dogs in group B (subgroup B1).


MEASUREMENTS AND MAIN RESULTS
The incidence of ventricular fibrillation was lower in group B (pre-existing stenosis) than in group A during the 10 min occlusion, though there was no difference in numbers of ventricular premature beats. Maximum ST segment elevation and maximum conduction delay were less in group B than in group A, but myocardial blood flow did not differ during the 10 min occlusion. In the subgroups the incidence of both types of ventricular arrhythmia was lower in subgroup B1 during the 10 min occlusion, while the maximum ST segment elevation and maximum conduction delay were less, and myocardial blood flow was greater.


CONCLUSIONS
Pre-existing 4 h coronary stenosis causes the development of collateral flow and reduces the incidence of ventricular arrhythmias during subsequent occlusion.