P330The erectile properties of myocardium

Background: Dipyridamole employed for stress imaging causes a three-to-fourfold increase in coronary blood flow (CFR) in normals, with an increase in left ventricular (LV) function due to the well known "erectile" properties of myocardium linking (non-linearly) increased flow to increased function.

Aim: To assess the relationship between LV contractile reserve and coronary flow reserve during dipyridamole stress.

Methods: We enrolled 111 patients (62 men; 68±10 years) with normal resting LV function. All underwent dipyridamole (0.84 mg/kg over 6 min) stress echocardiography with CFR evaluation of left anterior descending (LAD) by Doppler. Contractile reserve was calculated as peak stress from Real-Time 3D echocardiography (volumes) and cuff sphygmomanometer (pressure) as: ESP (end-systolic pressure)/ESV (end-systolic volume)- rest ESP/ESV. All patients underwent quantitative coronary angiography within 15 days (significant CAD criterion, ≥50% stenosis).

Results: In the subset of 92 pts with negative stress by standard wall motion criteria, contractile reserve was +3.7± 3.2 in the 43 pts without, vs -1.1±3.1 mmHg/mL/m2 in the 49 pts with coronary stenosis (p<.01). The relationship between LAD-CFR and changes in ESP/ESV was R = 0.5 in all patients, and R = 0.71 for the 25 patients with LAD single vessel disease (see figure). The combined criterion of reduced CFR (<2.0) and reduced contractile reserve had an overall accuracy of 74% (79% in those with normal regional wall motion at rest).

Conclusions: CFR is positively related to contractile reserve during vasodilator stress. The erectile properties of myocardium can help identify minor forms of CAD mirrored in blunted coronary and/or contractile reserve in presence of normal regional wall motion response.