New Technique for Myocardial Contrast Echocardiography in the Experimental Canine Model Using a Special Cannula for Selective Left Main Coronary Artery Cannulation

Abstract

Echocardiography has been used successfully as a tool for the evaluation of myocardial mass and function in open-chested animals and humans.'-'' However, myocardial contrast echocardiography is a new and experimental technique for assessing myocardial perfusion zones and blood flow in the open-chested animal mode1.12-20 Some investigators have injected contrast agents into the coronary circulation via a Gregg cannula positioned in the left main coronaryThe unique features of such an approach are that the cannula allows adequate mixing of the contrast agent and blood, thus preventing streaming, and allows for the evaluation of myocardial contrast washout characteristics at variable, controlled rates of coronary blood f l~w . '~-'~ Cannulation of the left main coronary artery in the dog using the Gregg cannula is, however, beset with major difficulties. A tie has to be placed around the left main coronary artery to secure the cannula in place. This artery is very short in the dog, and attempts at isolation of the artery frequently result in damage to the aorta, pulmonary artery, or coronary artery, causing significant bleeding. In addition, the cannula may obstruct the first septal perforator artery, resulting in ischemia of the interventricular septum. This artery is susceptible to injury because it arises from the left main coronary artery before its bifurcation into the left anterior descending and left circumflex coronary arteries. These technical prob!ems can result in significant animal attrition during preparation of the model. In this paper we describe a new cannula for injecting contrast agents during echocardiography that does not require isolation of the left main coronary artery and, when entering the left main coronary artery, does not occlude the first septal perforator arising proximal to the bifurcation of the coronary artery. DESCRIPTION OF THE CANNULAThis cannula is a modification of the standard Gregg cannula2' and is very similar to it (Fig. 1). Like the Gregg cannula, it must be introduced via the left brachiocephalic artery, with its tip guided into the left main coronary artery by palpation. The significant difference between this catheter and the Gregg cannula lies in the distal end, where a flange has been soldered. A 0.75-in.4ong tip is attached to the cannula distal to the flange and separated from it by a groove 0.64 cm wide. This tip has four side holes 0.055 in. in diameter spaced evenly around its circumference.These modifications of the Gregg cannula serve three important purposes. The flange prevents selective migration of the cannula into either the left anterior descending or the left circumflex coronary artery. As long as the aortic pressure is higher than the coronary perfusion pressure, the flange prevents the cannula from slipping out of the left main coronary artery. In addition, the distal tip allows easy manipulation of the cannula into the left main coronary artery. Finally, the holes in the tip prevent occlusion of the first septal perforator artery: a very proximal first...