N. Kumar, S. Choudhry

PURPOSE: Prospective study to examine the diagnostic accuracy of a new exercise-based parameter (abrupt steepening of HR response) in late exercise to diagnose macro-vascular CAD.
METHOD: 1000 CPX performed in symptomatic patients & 50 Angiograms in a single centre.
RESULTS: Patients without inducible ischemia have a linear HR response as a function of VO2 throughout exercise (Fig 1). Patients with inducible ischemia  develop mechanical dysfunction and a compensatory steepening of HR response (curvilinear) (Fig 2); this signifies clinically significant global ischemic burden. Fifty consecutive patients with an abnormal response underwent angiography.  The sensitivity and specificity for significant large vessel atherosclerosis (one or more vessels with >50% stenosis) was 92% (Fig 3).
CONCLUSION: In the contracting Ischemic Myocardium, an oxygen supply-demand mismatch results in diastolic dysfunction causing the stroke volume response to deteriorate and HR response to steepen with a progressively increasing work rate past the ischemic threshold.  This methodology is seen far more frequently than ST depression and is highly sensitive to the presence of a physiologically significant ischemic burden