Differing autonomic responses to dobutamine stress in the presence and absence of myocardial ischaemia

Cardiac autonomic dysfunction has prognostic significance in patients with coronary artery disease. This investigation aimed to assess changes in autonomic modulation induced by dobutamine stress in the presence and absence of myocardial ischaemia. In total, 314 individuals underwent dobutamine stress echocardiography to detect or exclude myocardial ischaemia. Simultaneous autonomic and haemodynamic data were obtained using a plethysmographic device. Total power spectral density and associated low-frequency (LF) and high-frequency (HF) power spectral components in absolute (ms(2)) and normalised units (nu) were determined. Participants were categorised as non-ischaemic (NI) or ischaemic (IS) responders. There were no significant differences in LFnu or HFnu between groups at baseline. At peak stress, LFnu decreased from baseline in NI (43 +/- 1.8 to 40 +/- 1.8%), but increased from baseline in IS responders (39.5 +/- 2 to 56 +/- 2%, P < 0.05). In contrast, HFnu increased in NI patients (57 +/- 1.8 to 60 +/- 1.8%) but decreased in IS responders (60.5 +/- 2 to 44 +/- 2%, P < 0.05). Those with a high ischaemic burden [more than three ischaemic left ventricular (LV) segments] had a greater increase in LFnu (41 +/- 4.8 to 65 +/- 3.2% vs. 44.8 +/- 3.8 to 57.7 +/- 3.1%, P < 0.05) and greater decrease in HFnu (59 +/- 4.8 to 35 +/- 3.2% vs. 55.2 +/- 3.8 to 42.3 +/- 3.1%, P < 0.05) compared to patients with a low ischaemic burden (1-3 ischaemic LV segments) respectively, at peak stress. In the absence of myocardial ischaemia, dobutamine stress is associated with a residual predominance of parasympathetic over sympathetic activity. Under conditions of ischaemia, there is a directionally opposite autonomic response with a significant residual increase of sympathetic over parasympathetic modulation. This response is augmented as the burden of ischaemia is increased.