Effect of arteriolar dilation on coronary artery diameter distal to coronary stenoses.

Previous studies have suggested that worsening hemodynamic severity of coronary stenoses in response to distal arteriolar dilation may be related to dilation of the normal epicardial artery adjacent to the stenosis resulting in increasing percent stenosis. To test this hypothesis we used sonomicrometry to continuously measure external circumflex coronary artery diameter distal to snare stenoses of varying severity in 19 open-chest dogs and 5 awake, chronically instrumented dogs. Arteriolar dilation produced by release of a transient coronary occlusion or by intracoronary injection of adenosine caused a decrease in circumflex coronary diameter distal to the stenosis. Regression analysis showed that circumflex diameter and pressure distal to the stenosis were directly related (mean r: transient occlusion, 0.86 +/- 0.04; adenosine, 0.97 +/- 0.01). The close relationship between pressure and diameter suggests that the decrease in diameter in response to arteriolar dilation was a passive effect. Passive coronary narrowing distal to a stenosis suggests that a similar effect may occur within a compliant stenosis, thus partly explaining the increase in severity of compliant stenoses in response to arteriolar dilation.