[Effects of reperfusion and coronary reocclusion on the variability of heart rate in patients with acute myocardial infarction]

Abstract

The aim of this study was to analyze the very early (first 24 hours) effect of successful or failed thrombolytic therapy on the autonomic nervous system. Thirty consecutive patients with a first acute myocardial infarction were enrolled in the study, and admitted to the Coronary Care Unit within 6 hours of the onset of symptoms and treated with systemic thrombolytic therapy. All patients underwent 24-hour Holter monitoring in order to analyze ST segment variation. The autonomic nervous system was evaluated by frequency-domain heart rate variability: low frequency/high frequency ratio (LF/HF) was measured at the beginning of Holter monitoring (T1), 15 min after reperfusion or 1 hour from the start of thrombolytic therapy (T2) and after 24 hours (T3). Reperfusion status was assessed by a > or = 50% reduction in ST segment elevation within 90 min of thrombolytic therapy, and early CK-MB peak. Early coronary reocclusion was detected by early reduction in ST segment elevation followed by stable ST segment re-elevation. Twenty patients (66%) showed successful thrombolytic therapy (Group 1), 5 patients (17%) had no evidence of successful thrombolytic therapy (Group 2) and 5 patients (17%) showed an early reocclusion (Group 3). LF/HF ratio values at T1 were similar in the three groups (5.66 +/- 1.7 vs 5.65 +/- 1.2 vs 5.51 +/- 0.9, NS). At T2, LF/HF ratio was significantly higher in Group 1 and 3 than Group 2 patients (9.21 +/- 1.7 and 11.1 +/- 1.2 vs 5.58 +/- 1.4, respectively, p < 0.001). In Group 1 LF/HF ratio was significantly lower at T3 when compared with T1 and T2 (1.9 +/- 1 vs 5.66 +/- 1.7 and 9.21 +/- 1.7, respectively, p < 0.001). Conversely, in Group 3 LF/HF ratio at T3 was similar to values measured at T1 (5.59 +/- 1.7 vs 5.51 +/- 0.9, respectively, NS) and significantly higher than those detected in Group 1. In Group 2, LF/HF ratio resulted substantially unchanged at T3 (5.49 +/- 1.7, NS). In conclusion, 1) successful thrombolytic therapy induces early beneficial effects on the autonomic nervous system function, as shown by increased heart rate variability values, when compared with failed thrombolytic therapy; 2) however, during the early period following coronary reperfusion, a transient but dramatic increase in sympathetic activity is observed. This could trigger coronary flow instability, thus facilitating reocclusion, by activating different pathogenetic mechanisms (increased vascular tone, platelet activation, thrombogenic factor prevalence); 3) early coronary vessel reocclusion precludes favorable effects of reperfusion on sympatho-vagal balance observed after the first 24 hours.