Very-low-frequency modulation of QRS slopes in patients with angina pectoris

This study was designed to investigate very-low-frequency modulation of QRS slopes in control electrocardiographic recordings of patients with stable angina pectoris admitted for prolonged elective percutaneous coronary intervention (PCI). This modulation occurs between 0.01Hz and 0.07Hz and has been described for QRS slopes as well as for heart rate variability (HRV). Results shows that power spectrum area in the modulation band (MB) and in the high-frequency (HF) band are larger for QRS downslope (I_DS) than QRS upslope (I_US). A differential Autonomic Nervous System (ANS) regulation at different ventricular regions, in addition to respiration or other mechanical effects, could explain this behavior. The same modulation was found in HRV and our results suggest that a relation between QRS slopes and HRV modulation exists. Whatever the source of the MB modulation is, its effect is much lower, in relative terms, for QRS slopes than for HRV.