Changes in autonomic nervous system activity: spontaneous versus balloon induced myocardial ischaemia

Aims Cardio-cardiac reflexes may be evoked by both myocardial ischaemia and coronary occlusion itself. The aim of the study was to assess the intrapatient behaviour of autonomic nervous system balance during spontaneous and balloon-induced coronary ischaemia. Methods and results We studied a group of patients admitted to the coronary care unit for acute coronary syndrome without ST-segment elevation who experienced spontaneous episodes of myocardial ischaemia during bed rest and ECG monitoring. The inclusion criterion was 80-90% lumen stenosis, amenable to angioplasty. Balloon coronary occlusion was performed at 4-6 atmospheres for 120 s. Autonomic nervous system activity was assessed by heart rate variability (HRV) analysis in frequency domain. We analysed 14 episodes of spontaneous ischaemia and 14 episodes of balloon coronary occlusion. During spontaneous ischaemia, HRV showed an increase in the low/high frequencies ratio (11.8 +/- 5.7), as compared to 5 min before and 5 min after (4.4 +/- 2.7 and 3.9 +/- 1.8, respectively) (p = 0.001). The opposite occurred during balloon coronary occlusion (0.8 +/- 0.4 vs. 3.9 +/- 2.0 and 5.1 +/- 2.1, respectively; p = 0.001). Conclusions Balloon inflation and occlusion evokes baroreceptor vagal predominance in response to a stretch stimulus of the coronary artery. Conversely, spontaneous occlusion during unstable angina is accompanied by naturally occurring sympathetic activation. Sympathetic activation may have a role in the natural history of the disease.