Objectives. We sought to elucidate the flow-function relation in chronic postischemic dysfunction during vasodilator stress. Background. In patients with ischemia 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 ischemia 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 a 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 a 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 a 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 a contractile reserve elicitable by a vasodilator stress more often exhibit residual flow reserve, whereas segments with a fixed or worsening mechanical response during stress show a flat flow response.
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