Effect of oral nitroglycerin and cold stress on myocardial perfusion in areas subtended by stenosed and nonstenosed coronary arteries☆

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Abstract

Physical obstruction and coronary vasoconstriction mediated by adrenergic stress are believed to be responsible for episodes of myocardial hypoperfusion and angina. Nitroglycerin relieves symptoms by reducing preload and dilating epicardial vessels. The net perfusion change and relation to stenosis severity of nitroglycerin and adrenergic stress have been debated. This study aimed to evaluate whether oral nitroglycerin and adrenergic stress alters perfusion in myocardial segments subtended by stenosed and nonstenosed coronary arteries. Myocardial perfusion was quantified (using N-13-ammonia positron emission tomography [PET]) at rest, after oral nitroglycerin 400 μg, and after cold stress in 25 patients with coronary artery disease (62 ± 9 years, 21 men) and in 30 controls (34 ± 9 years, 22 men). Myocardial perfusion was quantified in areas supplied by stenosed (>70%) and nonstenosed (<30%) coronary arteries. The cold pressor test did not significantly alter myocardial perfusion in any of the groups. However, when normalized for rate-pressure product, the response in stenosed areas showed a significantly more pronounced reduction compared with nonstenosed areas (0.78 ± 0.18 vs 0.64 ± 0.19 ml/g/min, p <0.005 and 0.86 ± 0.19 vs 0.73 ± 0.24 ml/g/min, p <0.05, p <0.05) for intergroup comparison. In both stenosed areas and nonstenosed areas nitroglycerin increased perfusion (0.51 ± 0.14 vs 0.60 ± 0.17 ml/g/min, p <0.05 and 0.56 ± 0.14 vs 0.61 ± 0.17 ml/g/min, p <0.05). Nitroglycerin did not alter myocardial perfusion in the control group. There was a negative correlation between the cold pressor test response and stenosis severity (r2 = 0.17, p <0.046), whereas this was not the case for nitroglycerin. In patients with coronary artery disease, myocardial segments supplied by stenosed coronary arteries showed an altered perfusion response to adrenergic stress. Oral nitroglycerin increased myocardial perfusion irrespective of the presence of a stenosis.

Section snippets

Study population:

The study population consisted of 25 patients (age 62 ± 9 years, 21 men) with angiographically verified 1- or 2-vessel CAD and a left ventricular ejection fraction >50%. Patients had to have ≥1 vessel with a minimum 70% diameter proximal stenosis and 1 vessel without any flow-limiting stenosis, defined as <30% diameter stenosis. Patients were included consecutively from a waiting list for percutaneus coronary intervention. All patients had stable angina pectoris and none of the patients had

Results

Table 1lists the hemodynamic measurements at rest, during the cold pressor test, after nitroglycerin administration, and before the ultrasound measurements. The cold pressor test increased systolic and diastolic blood pressure in both groups. Heart rate increased only in the patients with CAD, whereas nitroglycerin had no effect on hemodynamic parameters. Rate-pressure product differed slightly between the 2 baseline measurements (PET and ultrasound) in both groups.

Myocardial perfusion—effect of nitroglycerin:

Nitroglycerin has widespread vasodilatory effects1, 2, 12,29 and the overall effect on myocardial perfusion therefore depends on the balance between factors that increase and factors that decrease perfusion. Thus, the reduction in right ventricular filling pressure caused by peripheral venodilation tends to increase perfusion pressure and consequently perfusion.1 Similarly, dilation of epicardial arteries, albeit depending on the vessel size,2 increases perfusion via a reduction in coronary

Acknowledgements

The investigators would like to thank the bioanalysts, radio chemists, and physicists at the PET Center for their skilled assistance. They would also like to thank bioanalysts Bente Mortensen and Karin Boisen for performing the ultrasound scans and for PET flow calculations and data handling.

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    ☆

    This study was supported by the Danish Heart Association, Copenhagen, Denmark.

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