Assessment of internal thoracic artery vasoreactivity in response to sublingual nitroglycerin

We have previously shown the feasibility of assessing internal thoracic artery (ITA) size and blood flow hemodynamics before and after coronary artery bypass grafting using color-flow duplex ultrasound. This noninvasive method would be an ideal diagnostic tool for the evaluation of ITA graft status after therapeutic interventions in a patient with angina after coronary artery bypass grafting. The purpose of this study was to investigate the effects of nitroglycerin on the diameter and blood flow velocities of the left native ITA before coronary artery bypass grafting and the ITA graft postoperatively.

The study consisted of 24 male patients (mean age, 59 +/- 2.3 years) who had undergone elective coronary artery bypass grafting using a left ITA graft to the left anterior descending artery, with additional saphenous vein grafts. Color-flow duplex ultrasound (5.0-MHz transducer) was used for both the preoperative imaging of native ITAs and the postoperative study of ITA grafts before patient discharge. Repeated-measures analysis of variance was used to compare measurements of the ITA size and flow velocities (peak systolic velocity and end-diastolic velocity) at 5, 10, and 15 minutes after a single dose of sublingual nitroglycerin (0.4 mg) with the baseline values obtained without nitroglycerin.

The preoperative native left ITA and the postoperative left ITA graft diameters responded to sublingual nitroglycerin by showing a rapid and significant increase beginning at 5 minutes and lasting up to 15 minutes (p = 0.0001). Sublingual nitroglycerin caused the peak systolic velocity of the native left ITA to be augmented at 5 minutes (p = 0.0002), and this effect was still apparent at 10 minutes (p = 0.0001) and 15 minutes (p = 0.0192). However, postoperative left ITA graft peak systolic velocities remained unaffected by the sublingual nitroglycerin (p = not significant).

We conclude that instantaneous noninvasive measurement of ITA graft size and blood flow velocities after a therapeutic drug intervention may be clinically useful, particularly in a post-coronary artery bypass grafting patient with recurrent angina.