Coronary blood flow in evolving myocardial infarction preceded by preinfarction angina: a critical reevaluation of preconditioning effects in clinical cases

This study was undertaken to reevaluate the protective effects of preinfarction (pre-MI) angina in acute MI. The mechanisms involved in the apparent protective effects of pre-MI angina have been presumed to be preconditioning effects as defined by experimental studies. The phenomenon, has not, however, been observed in diabetic and/or elderly patients or in those treated by primary percutaneous coronary intervention (PCI). A total of 202 patients with anterior wall MI without a history of MI who underwent primary PCI with coronary balloon dilation and stenting (rate: 50%) <6 hours after onset were studied. Patients included 59 with pre-MI angina (group 1) and 143 without pre-MI angina (group 2). The infarct-related coronary artery was patent on admission in 46% of group 1 and 31% of group 2 (p=0.045). Thrombolysis in Myocardial Infarction (TIMI) 1-2 flow was significantly more frequent in group 1 (29%) than in group 2 (11%, p=0.005) on admission. Among risk factors, clinical background, coronary anatomy, and clinical outcome, the only significant predictor of pre-MI angina was a patent infarct-related coronary artery on admission (odds ratio: 2.39, p = 0.015). There was no significant difference in left ventricular ejection fraction, peak creatine kinase, or the incidences of heart failure and in-hospital/follow-up deaths between these groups. In conclusion, the findings suggest that the protective effects reported in MI with pre-MI angina treated by thrombolysis are due to more fragile thrombotic occlusion, which can be more easily recanalized by thrombolysis, whereas the beneficial effects are not evident in those treated by primary PCI.