Coronary Vasomotor Tone
Background. Coronary artery reference diameters increase during coronary angioplasty (PTCA). However, in clinical practice, balloon selection is often based on a preceding diagnostic coronary angiogram. It is common to find that the initially selected balloon is undersized due to resting vasomotor tone. This may contribute to a suboptimal angioplasty result.

Methods. Quantitative coronary angiography (QCA) was used to determine the magnitude of coronary artery vasodilatation over baseline angiography and its impact on balloon size choice. Pre-PTCA clinical and treatment variables were analyzed for their potential contribution to resting vasomotor tone.

Results. QCA of reference coronary diameters was performed in a group of 103 patients undergoing PTCA. Post PTCA proximal and distal reference diameters significantly increased over baseline. The average increase of the proximal segment was 0.368 mm (13.6%) p < 0.001 and of the distal segment 0.567 mm (24.8%) p < 0.001. The initial nominal balloon diameter was smaller than the post PTCA proximal segment by an average of 0.34 mm (12.6%) p < 0.001. Of the clinical and treatment variables examined age < 65 years and pre-PTCA beta blocker use, significantly affected baseline vasomotor tone p < 0.05.

Conclusions. Routine diagnostic angiography underestimates the true diameter of the coronary artery. Due to baseline vasomotor tone, coronary reference segments can be expected to increase approximately 13% in diameter during successful PTCA. Patients under 65 years of age and those using beta-blockers may have a significantly increased baseline vasomotor tone. Underestimation of coronary artery diameter based on initial angiography necessitated a second, larger balloon in 16.5% of cases.

The success of percutaneous transluminal coronary angioplasty (PTCA) is influenced by the balloon diameter used1,2 relative to the native coronary artery. Either overdilation or underdilation decreases the likelihood of success. During PTCA the choice of balloon size is determined by visual estimates of coronary diameter on preceding angiography. As was shown for lesion severity, visual estimation is subjective and highly variable. It is common, during PTCA, to replace the initial balloon with a balloon of larger diameter. One reason is that the normal reference coronary segments vasodilate during PTCA [due to intracoronary (IC) nitroglycerin (Ntg), contrast, and changes in flow] causing the operator to revise his initial assessment of the coronary artery diameter as an underestimation.

To examine the effect of changes from baseline vasomotor tone during PTCA on usual practice, we measured normal reference coronary artery diameters in the stenotic coronary artery, pre- and post-PTCA. The frequency with which initial underestimation necessitated dilation with a larger balloon was calculated. Clinical and treatment variables potentially influencing baseline coronary artery vasomotor tone (age, sex, smoking,6 hypertension (HBP), diabetes mellitus (DM), medications [beta-blockers, intravenous (IV) Ntg], ejection fraction (EF), recent myocardial infarction (MI), and stenosis (location and severity) were examined for a significant effect.