Heart rate variability during the first 24 hours of acute myocardial infarction

BACKGROUND: To evaluate the heart rate variability (HRV) during the first 24 h after a myocardial infarction (MI), and to study its relationship with other clinical variables and in-hospital follow-up. PATIENTS AND METHODS: 101 patients (age < 80 years) with MI in sinus rhythm were prospectively studied. A Holter monitoring was performed during the first 24 h. The heart rate (HR), standard deviation of RR intervals (SDRR) and the histogram at different levels were analyzed, as well as the mean and standard deviation of RR intervals in an early 5 min record. The results were compared with the clinical characteristics and the in-hospital outcome of the patient. RESULTS: HRV was lower in women, hypertensives and patients who did not receive thrombolytic agents. In patients without heart failure, inferior MI's had lower HR and higher HRV than anterior MI's (SDRR: 52.8 [20.6] and 42.2 [16.9], respectively; p < 0.05). HRV was significantly decreased as Killip group increased, as well as in patients who developed late heart failure. The development of ventricular tachycardia or fibrillation was associated to a low HRV in the 24 h analysis (SDRR: 30.2 [15.6] for the 6 patients with VF/VT vs 46.8 [20.1] for the rest; p < 0.05), as well as in the early 5 min record (29.8 [14.8] and 50.8 [35.8], respectively; p < 0.05). CONCLUSIONS: During the first 24 h after MI the HRV is related to some clinical variables and to MI location (higher in inferior MI). Patients who develop heart failure or ventricular arrhythmias before hospital discharge have a higher HR and a significantly decreased HRV.