Diabetes and ST Elevation Myocardial Infarction: How successful is intravenous thrombolysis for the diabetic heart?

Early resolution of ST-segment elevation is associated with enhanced clinical outcome following ST elevation myocardial infarction (STEMI). According to previous studies, the incidence of successful reperfusion following STEMI treated with thrombolytic regimen is similar for type 2 diabetic subjects and nondiabetic subjects as assessed by “snapshot” electrocardiographic or angiographic criteria (1). Nevertheless, type 2 diabetic subjects thrombolysed because of STEMI still seem to fare worse, manifesting impaired left ventricular function or long-term prognosis (2).

The aim of this prospective study was to test the hypothesis that type 2 diabetic subjects may have a protracted ST-segment recovery, even while achieving reperfusion criteria, compared with nondiabetic subjects. Therefore, continuous ST-segment monitoring was used, as it is considered to be more reflective not only of infarct-related artery patency status, but of actual tissue reperfusion (3).

The study cohort included 137 patients with STEMI: 105 nondiabetic subjects and 32 type 2 diabetic subjects (age 58.9 ± 10.3 vs. 67.5 ± 7.1 years, respectively; P < 0.001) without history of prior myocardial infarction or coronary artery bypass surgery. Each patient received either streptokinase or tissue-type plasminogen activator (t-PA) in ≤6 h from index pain and was connected to the Eagle 4000 Monitor immediately after admission. All patients integrated to this study attained the criterion of steady ≥50% ST-segment recovery within 90 min after thrombolysis initiation. Significant differences in the two groups were not found concerning time elapsed from index pain to initiation of thrombolytic procedure, location of STEMI, or thrombolytic agents used.

The time required for ≥50% ST-segment steady resolution was significantly greater in type 2 diabetic subjects than in nondiabetic subjects (68.8 ± 15 vs. 45.8 ± 17.9; P < 0.001). Moreover, the former had higher subsequent peak creatin kinase myocardial type B isoenzyme release than the latter (P < 0.001). According to multivariate linear regression analysis, type 2 diabetic subjects were independently and positively related to the time for ≥50% ST-segment recovery (P < 0.001).

In accordance to the original hypothesis, the present study showed that type 2 diabetic subjects required almost 50% more time to achieve satisfactory ST-segment elevation recovery. The diminished benefit from thrombolysis may be attributed to several diabetes-induced disorders from diffuse coronary artery disease, metabolic derangements, complexity of the culprit atheromatic plaque, microangiopathy including endothelial dysfunction, and diminished flow reserve, to impaired glucose utilization and accumulation of fatty acid intermediates (4). The results of the present study imply that the retardation in achievement of satisfactory reperfusion in the myocardial cells, as assessed by ST-segment elevation resolution, may at least partially account for the subsequent detrimental effect on diabetic hearts when suffering STEMI. If these findings are validated with larger studies, a more aggressive therapeutic approach might prove suitable for type 2 diabetic subjects with STEMI.