Flow-Function Relation in Patients With Chronic Coronary Artery Disease and Reduced Regional Function: Positron Emission Tomographic and Two-Dimensional Echocardiographic Study With Coronary Vasodilator Stress

Objectives. We sought to elucidate the flow-function relation in chronic postischemic dysfunction during vasodilator stress. Background. In patients with ischemi and regional dysfunction, stress echocardiography can elicit three responses in the dysfunctioning segments: no change, improvement or worsening. The physiology underlying these responses is unclear. Methods. Seventeen patients with ischemi and left ventricular dysfunction underwent evaluation of regional function by two-dimensional echocardiography and myocardial blood flow by positron emission tomography and 13N-ammonia. Flow (ml/min per g) and function (regional wall motion score [RWMS] from 1 = normal to 4 = dyskinetic) were evaluated both at rest and after dipyridamole (0.56 mg/kg body weight over 4 min). Results. In 45 normal segments, rest to dipyridamole flow increased from 0.83 ± 0.22 (mean ± 1 SD) to 1.87 ± 0.90 (p < 0.01) with hyperkinetic contraction pattern. Among dysfunctioning segments, responders (n = 11) showed an upsloping flow-function curve during stress (i.e., increased function [RWMS rest 2.5 ± 0.5 vs. dipyridamole 1.2 ± 0.4] and increased flow [rest 0.69 ± 0.30 vs. dipyridamole 1.89 ± 1.43, p < 0.01]); nonresponders (n = 20) had flat flow-function curve during dipyridamole (i.e., fixed function [RWMS rest and dipyridamole 2.6 ± 0.5] and no flow increase [rest 0.64 ± 0.24 vs. dipyridamole 0.87 ± 0.51, p = NS): Ischemic segments (n = 9) exhibited downsloping flow-function curve during dipyridamole (i.e., worsened function [RWMS rest 2 ± 0.5, dipyridamole 3.1 ± 0.6] and no significant flow change [rest 0.67 ± 0.29 vs. dipyridamole 0.79 ± 0.23, p = NS]). Conclusions. Myocardial segments with rest dysfunction and contractile reserve elicitable by vasodilator stress more often exhibit residual flow reserve, whereas segments with fixed or worsening mechanical response during stress show flat flow response.