NO EVIDENCE FOR ISCHEMIC PRECONDITIONING DURING REPEATED VESSEL OCCLUSION IN CORONARY ANGIOPLASTY

Coronary angioplasty has been the favoured model in studying ischemic preconditioning in humans, but results have remained controversial, po ssibly due to some artefacts related to coronary balloon angioplasty a s an ischemia model. We examined this issue by monitoring the sequenti al metabolic, functional and neurohumoral changes during repeated vess el occlusion in coronary angioplasty performed in patients with chroni c angina pectoris. Two groups of patients undergoing two successive ba lloon inflations of approximately 2 min duration were studied. These b alloon inflations were preceded by a short inflation performed immedia tely after introduction of the balloon into the stenosis. The aim of t his primary inflation was to establish adequate coronary blood flow wi th the deflated balloon in the stenosis and to guarantee that the subs equent two balloon inflations were truly comparable in time. Group I c onsisted of 23 patients, in whom the changes in the degree of angina, pulmonary capillary wedge pressure (PCWP), atrial natriuretic peptide (ANP) and circulating catecholamines during the procedure were studied . The sequential changes in myocardial metabolism were monitored in gr oup II of nine patients by determining the lactate extraction ratios a nd femoroarterial coronary sinus (Fa-CS) differences in pH and pCO(2) before and after each balloon inflation. In group I, PCWP and total ca techolamines increased similarly during both balloon inflations, but A NP remained unchanged. In group II patients the lactate extraction rat ios turned negative, the Fa-CS pH-differences increased and the pCO(2) -differences decreased during vessel occlusions, the changes being som ewhat more prominent during the second balloon inflation. To study ada ptation to ischemia, the group I patients were divided into two subgro ups with and without signs of ischemic dysfunction during balloon infl ations (PCWP increase > 5 mmHg and < 5 mmHg, respectively), and the gr oup II patients were divided into two subgroups with and without metab olic ischemia (lactate-producers and non-producers). The ANP levels we re constantly higher in the patients demonstrating ischemic dysfunctio n during balloon inflations, but catecholamine levels increased only a fter the second balloon inflation. The anginal pain experienced by the patients and the signs of metabolic ischemia were identical during bo th balloon inflations. We conclude that acute ischemic preconditioning does not occur in patients with repeated vessel occlusions of approxi mately 2 min duration. The patients without ischemia during the proced ure had more critical stenoses and pre-existing collaterals. However, other protective mechanisms, such as chronic adaptation at the cellula r level or recruitment of new collaterals, cannot be excluded.