Regional dynamic behaviour of the canine myocardium following brief ischaemia: wall thickness, wall thickening and blood flow.

Regional myocardial wall characteristics were studied in open-chest anaesthetised dogs. End-diastolic wall thickness and systolic wall thickening were measured by echocardiography and blood flow was quantified by the local 133Xe washout technique during and following coronary artery occlusion of 10 s to 10 min duration. End-diastolic wall thickness exhibited a small temporary increase over baseline value during reperfusion. Maximum value was observed following ischaemic periods of 1 min duration (9.0 +/- 0.5 mm [(Mean +/- 2 SEM) versus a baseline value of 8.2 +/- 0.5 mm (P less than 0.01)]. A post-ischaemic, hyperkinetic and transient systolic wall thickening was most prominent following periods of 2 min of ischaemia (7.1 +/- 0.7 mm; baseline value 4.2 +/- 0.2 mm, P less than 0.01). Extension of ischaemia from 2 min to 10 min provoked no essential change of reactive hyperaemia characteristics (maximum blood flow 257.6 +/- 27.4 cm3 . min-1 . 100 g-1 versus 238.3 +/- 57.0 cm3 . min-1 . 100 g-1, P less than 0.05; duration 62.8 s versus 71.8 s, P less than 0.05). Such extension of the ischaemia, however, made the post-ischaemic, hyperkinetic systolic and transient wall thickening disappear. Considerable asynchrony between variations of blood flow, wall thickness and wall thickening was observed. Determinants with influence on post-ischaemic wall thickness and wall thickening are discussed in relation to the data presented. The resultant of these determinants increasingly favours transient post-ischaemic hyperkinesia following ischaemia of up to 2 min duration, whereas further prolongation of the ischaemia will result in progressive impairment of the myocardial function during reperfusion.