Noninvasive transthoracic low frequency ultrasound augments thrombolysis in a canine model of acute myocardial infarction - Evaluation of the extent of ST-segment resolution

Background: Recently it has been demonstrated that transcutaneous delivery of ultrasound combined with tissue plasminogen activator (tPA) is more effe ctive than tPA alone in recanalizing acutely thrombosed canine coronary art eries. In the present study, we investigated the incidence of partial (grea ter than or equal to 50%) and complete (greater than or equal to 70%) ST-se gment elevation resolution in the precordial leads of dogs with experimenta l acute myocardial infarction that were treated with tissue plasminogen act ivator (tPA) alone or in combination with noninvasive transcutaneous delive ry of high-intensity low frequency (27[emsp3 ]kHz) ultrasound. Methods: Thrombotic coronary occlusions were induced in the midportion of l eft anterior descending (LAD) coronary artery by electrical injury in 24 do gs. All dogs were given intravenous heparin and tPA. Dogs were randomized t o tPA alone (n=12) or combined tPA and adjunctive transcutaneous ultrasound (US) delivery (n=12). Electrocardiograms were recorded at 1) baseline, 2) after coronary occlusion just before initiation of therapy, 3) when coronar y angiography showed recanalization of the coronary artery (or at 90 minute s after initiation of therapy if reperfusion did not occur before then) and 4) 90 minutes later. ST amplitude was measured in all 6 precordial leads. Results: ST-segment amplitude at baseline was comparable between the tPA an d the US group. Before initiation of therapy, sum of ST-segment elevation t ended to be higher in the US group. At reperfusion and 90 minutes thereafte r, sum of ST-segment amplitude tended to be smaller for the US group than i n the tPA group (p <0.001 for the time effect; p=0.118 for the time x group interaction). Up to 90 minutes after initiation of therapy greater than or equal to 50% resolution of the sum of precordial ST elevation was detected in 7 out of 11 dogs (63.6%) in the tPA group versus 10 out of 11 dogs (90. 9%) in the US group. Ninety minutes thereafter, 3 out of 7 dogs in the tPA group (42.9%) versus 9 of 11 dogs in the US group (81.8%) had greater than or equal to 50% resolution of the sum of precordial ST elevation. Conclusions: The combination of tPA with noninvasive transcutaneous deliver y of low frequency high-intensity ultrasound resulted in greater resolution of ST-segment elevation when reperfusion occurs and 90 minutes thereafter, as well as a higher rate of epicardial coronary artery reperfusion. Abbreviated abstract. We investigated the incidence of partial (greater tha n or equal to 50%) and complete (greater than or equal to 70%) ST-segment e levation resolution in the precordial leads of dogs with experimental acute myocardial infarction that were treated with tissue plasminogen activator (tPA) alone or in combination with noninvasive transcutaneous delivery of h igh-intensity low frequency (27[emsp3 ]kHz) ultrasound. The combination of tPA with noninvasive transcutaneous delivery of low frequency high-intensit y ultrasound resulted in greater resolution of ST-segment elevation when re perfusion occurs and 90 minutes thereafter, as well as a higher rate of ang iographic epicardial coronary artery reperfusion.