Balloon occlusion during coronary angioplasty as a model of myocardial ischaemia: reproducibility of sequential inflations

In order to evaluate the potential of balloon occlusion during coronary angioplasty as a model of myocardial ischaemia in man we have measured coronary sinus blood flow (CSBF), myocardial oxygen consumption (MVO2), lactate extraction (LER) and electrocardiographic changes in 11 patients undergoing left anterior descending artery (LAD) angioplasty. Baseline measurements were made before balloon crossing and between inflations. Four consecutive inflations each of 60 s duration were made; 5 min return to baseline was allowed between inflations. There was a significant reduction in CSBF and MVO2 (ml min−1) during inflations 2, 3 and 4 (CSBF: 121±66→94±53, 113±49→99±42, 124±66→102±41, P<0.02; MVO2:11.3±6.6−9.1±3.9, 10.4±3.7−8.7±2.4, 12.2±4.4→9.4±2.8, P<0.05). However during the first period of balloon occlusion there were inconsistent changes in coronary flow with an overall rise in mean flow (97±35→128±80 ml min−1, P = NS) and an overall rise in mean myocardial oxygen consumption (9.6 ± 3.8→12.5 ± 7.5 ml min−1, P = NS). There was lactate production during all four inflations but the changes during the first one did not achieve statistical significance. These inconsistent changes during the first inflation were thought to be due to partial obstruction of the stenosis by the deflated balloon before primary dilatation. The changes due to crossing and during the first two inflations were further investigated in another group of 12 patients undergoing LAD angioplasty. Great cardiac vein flow (GCVF), CSBF, MVO2 and LER were recorded at baseline, during crossing and during the first two inflations. With the deflated balloon across the stenosis there were no changes in CSBF or MVO2 but there was a fall in GCVF (103±28→77±50, P = NS) and a significant fall in LER (77±57→16±37, P<0.01). Although there was a fall during the first inflation in CSBF, GCVF, MVO2 and lactate extraction none of these changes were significant. During the second inflation these changes were of greater magnitude and achieved statistical significance. While balloon occlusion during coronary angioplasty has the potential of providing a model of ischaemia in man we have found the first inflation period unreliable, due to the variable degree of occlusion by the deflated balloon. We suggest that only subsequent inflations after the primary dilatation are used for observations. These findings are of significance when evaluating the effects of therapeutic interventions during PTCA. Various refinements in measurements of the effects of ischaemia will improve the specificity of the model.