Relationship between heart rate changes during reflex tests and heart rate variability in patients with recent myocardial infarction

Background. Low heart rate variability (HRV) reflecting predominance of sympathetic tone is an independent predictor of sudden cardiac death after myocardial infarction (MI). We have previously shown that decreased heart rate (HR) response during reflex tests (breathing 6 per minute and Valsalva maneuver at the end of the first week after MI is also associated with elevated risk of sudden death during subsequent 2 years. Aim. To elucidate relationship between HIR response to breathing 6 per minute and Valsalva maneuver, and HRV as standard non-invasive method of assessment of autonomic regulation of the heart. Material. Tests with breathing 6 per minute and Valsalva maneuver were performed on 4-11 (median 8) days of MI in 188 patients (68.1% males) aged 34-75 (median 62) years, 93.6% of whom received beta-blockers. Parameters studied were difference between maximal and minimal HR during 1st min of controlled breathing (DeltaHR) and Valsalva ratio (VIR). Standard time- and frequency-domain HRV measures were calculated from 15-min ECG strips at bed rest just before tests and from 24-hour ECG recordings after tests. Results. In patients with low values of DeltaHR (<3.36) and VIR (<1,13) most of HRV parameters were also significantly decreased. Most close association was found between low DeltaHR and low SDNNi and LF power calculated from 24-hour Holter recordings, between low VIR and low LF power at bed rest. Conclusion. Direct correlation between HIR response to reflex tests and parameters of HRV allows to suggest that decreased HIR response to controlled breathing and Valsalva maneuver in patients with recent MI also reflects presence of marked sympathetic predominance.