Background Obstructive coronary artery disease (CAD) is evident in only half of patients referred for diagnostic coronary angiography. Five-minute heart rate variability (HRV) is a marker for autonomic control of the vasculature, which we hypothesised could be used to risk-stratify cardiac patients (the Alternative Risk Markers in Coronary Artery Disease (ARM-CAD) study.

Methods Resting HRV prior to elective coronary angiography was analysed in 470 participants with predominantly normal cardiac rhythm, regardless of comorbidity. The presence of obstructive CAD (≥50% stenosis) was regressed in a multivariate model including risk factors, ECG variables and medications.

Results Mean age was 65 years (SD 11), 67% were male, 21% had diabetes, mean blood pressure was 144/79 mm Hg (SD 21/10) and 16% had impaired left-ventricular function. Patients with obstructive CAD had significantly reduced HRV, particularly in the low frequency (LF) range (median 180 vs 267 ms² without CAD; p<0.001). There was a linear trend according to the severity of CAD; the median LF power (IQR) in patients with normal coronaries was 275 (612), with minor coronary irregularities 255 (400), single-vessel CAD 212 (396) and more severe disease 170 (327) ms²; p-value for trend=0.003. There was a similar reduction in LF power regardless of the anatomical location of coronary stenoses (see Abstract 61 figure 1). Comparing patients with LF<250 and ≥250 ms², the OR for obstructive CAD was 2.42, 95% CI 1.33 to 4.38 (p=0.004) after adjusting for risk factors, medications and heart rate. No interactions were noted in sub-group analysis of age, gender, diabetes, prior cardiovascular disease or high-sensitivity CRP. In addition, HRV added to risk prediction irrespective of baseline Framingham risk (p<0.0001).

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Abstract 61 Figure 1

Conclusion Low HRV is strongly predictive of angiographic coronary disease regardless of other comorbidities and is clinically useful as a risk predictor in patients with sinus rhythm.