Assessment of coronary conductance and resistance vessel reactivity in response to nitroglycerin, ergonovine and adenosine: in vivo studies with simultaneous intravascular two-dimensional and Doppler ultrasound.

OBJECTIVES

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.

BACKGROUND

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.

METHODS

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).

RESULTS

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.

CONCLUSIONS

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.