Sublingual Nitroglycerin Dilates Coronaries on CTA

The objective of a recent study was to evaluate the effect of sublingual nitroglycerin spray on coronary vessel visibility, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) on coronary CT angiography (CTA).

Sublingual nitroglycerin given 5 minutes prior to coronary CT angiography causes dilatation of coronary arteries and a greater number of septal branches arising from the proximal and mid left anterior descending coronary artery to be visualized.

Participants
21 patients who did not and 21 who did receive a single dose of sublingual nitroglycerin (0.4 mg/L) 5 minutes prior to scanning.

Methodology
CTAs were performed with a 64-MDCT. Patients with heart rates >65 bpm received a beta-blocker. The number of septal branches arising from the proximal and mid left anterior descending artery (LAD) and the number of times the sinoatrial branch and conus branch were visualized arising from the right coronary artery (RCA) were counted.

The SNR of the left ventricular myocardium was measured, which was the ratio of attenuation in myocardium and image noise. The SNR of several coronary arteries was measured, which was the ratio of attenuation in the lumen of the artery to image noise, and image noise was the standard deviation of the attenuation of the artery.

The CNR of several coronary arteries was measured, which was the difference between attenuation of the lumen of the artery and fat attenuation surrounding the artery divided by image noise. Vessel volume and average vessel diameter of the LAD and RCA were measured.

A segmentation software algorithm calculated volume. Artery diameter measurements were made in a plane perpendicular to a curved multiplanar reconstruction along the long axis of the vessel. Side effects of headache, reflex tachycardia, and drop in blood pressure due to nitroglycerin were recorded.

Results
Average lumenal diameter of the RCA for patients who were not and were given nitroglycerin was 2.63 mm and 3.48 mm, respectively. Average diameter of the LAD for patients who were not and were given nitroglycerin was 2.67 mm and 3.42 mm, respectively. Average volume of the RCA for those who were not and were given nitroglycerin was 0.58 cm3 and 1.05 cm3, respectively. For the LAD, average volume was 0.35 cm3 and 0.72 cm3, respectively, for those who were not and were given nitroglycerin.

There were significantly more septal branches visualized in those given nitroglycerin.

A sinoatrial branch and conus branch were seen more often in those given nitroglycerin, but this difference was not statistically significant. There was no significant difference in the SNR and CNR between groups. Side effects were not significantly different between groups.

Conclusions
Sublingual nitroglycerin causes dilatation of coronary arteries without compromising image quality.

Reviewer’s Comments
The editor of this article notes that patients should not have taken Viagra (sildenafil), Cialis (tadalafil), or Levitra (vardenafil) within 24 hours if they are to be given nitroglycerin, as severe side effects have been reported.

Author: : Vineet R. Jain, MD

Reference: :
Decramer I, Vanhoenacker PK. Effects of Sublingual Nitroglycerin on Coronary Lumen Diameter and Number of Visualized Septal Branches on 64-MDCT Angiography. AJR; 2008; 190 (January): 219-225