The aim of this study was to determine the differential effects of nitroglycerin,
ergonovine and adenosine on the resistance vessels in vivo by using a Doppler-tipped
guide wire in combination with an ultrasound imaging catheter.
Catheter-based two-dimensional intravascular ultrasound yields images of the coronary
arteries from which cross-sectional areas can be measured. Intravascular Doppler ultrasound
techniques allow measurement of coronary blood flow velocity. The simultaneous use
of the two techniques can yield anatomic and physiologic information on conductance
and resistance vessels but has not been tried in the coronary arteries.
In 15 dogs, we studied coronary flow and vascular reactivity in response to pharmacologic
agents using two approaches: 1) a 30-MHz, 4.3F imaging catheter placed alongside a
0.018-in. (0.046 cm) Doppler wire in the circumflex or left anterior descending coronary
artery (n = 5); 2) the ultrasound imaging catheter introduced directly over a 0.014-in.
(0.036 cm) Doppler wire (n = 10). Vasodilator and vasoconstrictor responses were studied
by using intracoronary nitroglycerin (50, 100 and 200 micrograms), ergonovine (200
micrograms) and adenosine (6 mg).
Nitroglycerin caused a dose-dependent increase in epicardial coronary artery cross-sectional
area and, to a lesser extent, in average peak flow velocity, resulting in an increase
in volumetric coronary blood flow of 39% and 50% at the doses of 100 and 200 micrograms,
respectively. With these doses of nitroglycerin, the decrease in diastolic to systolic
velocity ratio and the increased change in cross-sectional area from end-diastole
to end-systole suggested an enhanced epicardial coronary artery compliance. With ergonovine,
a 12% reduction in epicardial coronary artery cross-sectional area was seen, without
a significant change in average peak velocity, resulting in a 15% decrease in volumetric
coronary blood flow. Adenosine caused a 270% increase in average peak velocity but
no change in epicardial coronary artery cross-sectional area, resulting in a 270%
increase in volumetric blood flow.
This study demonstrates that nitroglycerin and ergonovine predominantly influence
coronary conductance arteries whereas adenosine mainly dilates coronary resistance
vessels. These findings also demonstrate that the combined use of a two-dimensional
and a Doppler ultrasound transducer within one catheter assembly can provide information
on the differential effects of vasoactive agents on the epicardial and microvascular
coronary circulation.