HEART-RATE-VARIABILITY DURING THE FIRST 24 HOURS OF SUCCESSFULLY REPERFUSED ACUTE MYOCARDIAL-INFARCTION - PARADOXIC DECREASE AFTER REPERFUSION

Heart rate variability (HRV) was evaluated during the first 24 hours o f hospitalization in 36 patients with acute myocardial infarction. Rep erfusion was achieved by 60 minutes in 21 patients (group M1) and by 1 30 minutes in the remaining 15 (group M2). Mean 24-hour HRV measures w ere not significantly different between groups M1 and M2. Hourly spect ral analysis revealed a decrease in total power (0.01 to 1.0 Hz) from 0 to 8 hours to 9 to 16 and 17 to 24 hours in groups M1 (7.04 +/- 0.27 to 6.94 +/- 0.23 and 6.52 +/- 0.18; p = 0.0006) and in group M2 (6.88 +/- 0.30 to 6.57 +/- 0.23 and 6.40 +/- 0.15; p = 0.002). Total power decreased immediately after reperfusion: in group M1 it decreased duri ng the second hour (7.32 +/- 0.96 to 6.42 +/- 1.2; p = 0.001) and in g roup M2 during the third (7.47 +/- 1.2 to 6.73 +/- 1.4; p = 0.049) and fourth hours (7.47 +/- 1.2 to 6.48 +/- 1.4; p = 0.029). Mean change i n total power in the second hour was -11.8% in group M1 and +3.9% in g roup M2 (p = 0.0001) and in the third hour, +14.5% in group M1 and -8. 6% in group M2 (p = 0.006). During the remaining 21 hours, there was n o significant difference in hourly change in total power between group s. Similar changes were noted in high-frequency power, but the ratio o f low-frequency to high-frequency power was unchanged. In acute myocar dial infarction, HRV is higher during the early phase and decreases as hours progress. Reperfusion causes an immediate, transient, and seemi ngly paradoxic decrease in HRV, probably because of an abrupt decrease in parasympathetic tone.