Although angiotensin converting enzyme (ACE) inhibitors have been reported to increase coronary blood flow, the effect of selective angiotensin II (AT1)-receptor antagonism on the coronary ...circulation has not been defined.
We examined the effects of the AT1-receptor antagonist Losartan (DuP 753, 0.2-3.2 mg/kg) on coronary arteries in vivo in 11 dogs, using a combination of intravascular two-dimensional and Doppler ultrasound. In six dogs, a 30-MHz, 4.3F ultrasound imaging catheter was placed in the midsegment of the circumflex coronary artery to measure cross-sectional area (CSA), and a 0.018-in. Doppler wire was placed alongside to measure coronary flow velocity. At peak effect (1.6 mg/kg), Losartan increased mean coronary CSA from 7.9 +/- 0.5 to 9.5 +/- 0.8 mm2 and average peak velocity (APV) from 32 +/- 10 to 56 +/- 18 cm/sec, resulting in an increase in coronary blood flow from 74 +/- 19 to 151 +/- 36 mL/min. The maximal effect of the ACE inhibitor enalaprilat (5 mg) was an increase in CSA from 7.7 +/- 0.7 to 8.4 +/- 0.8 mm2 and an increase in APV from 36 +/- 10 to 53 +/- 20 cm/sec, with an increase in coronary blood flow from 82 +/- 25 to 122 +/- 41 mL/min. Relative to maximal hyperemia with adenosine (6 mg i.c.), the magnitude of flow increase from baseline was 0.37 with the AT1-receptor antagonist and 0.19 with the ACE inhibitor (p < 0.05). These effects were seen without changes in heart rate or systemic arterial pressure. In an additional five dogs, the ultrasound imaging catheter was introduced directly over a 0.014-in. Doppler wire, and the effects of indomethacin, propranolol, and N omega-nitro-L-arginine methylester (L-NAME) on the vasodilator effect of Losartan (1.6 mg/kg) were examined. Indomethacin and propranolol had no effect on Losartan-induced vasodilation, suggesting that it was not mediated via prostaglandins or beta-adrenoceptors. However, Losartan-induced epicardial vasodilation was partially inhibited by L-NAME, suggesting an action partly dependent on endothelial release of nitric oxide.
Thus, these acute studies in anesthetized dogs suggest that inhibition of AT1-receptors in the coronary circulation results in vasodilator responses greater in magnitude than ACE inhibition and partly endothelium dependent. The exact role for AT1-receptors in human coronary physiology and pathology remains to be defined.
Objectives. The aim of this study was to determine the differential effects of nitroglycerin, ergonovine and adenosine on the resistantce 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 Bow 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 μg), ergonovine (200 μg) 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 59% at the doses of 100 and 200 μg, 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 bood 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.
Previous studies conducted in high-risk populations have reported high predictive values and accuracies for diagnostic imaging techniques for aortic dissection. To see how these techniques perform in ...low-risk populations, we used Bayes' theorem to calculate predictive values and accuracies for angiography, CT, MRI, and TEE. In high-risk populations (disease prevalence = 50%), positive predictive values were all greater than 85%. In intermediate risk populations (disease prevalence = 10%), positive predictive values were greater than or equal to 90% for CT, MRI, and TEE, but were 65% for angiography. In low-risk populations (disease prevalence = 1%), positive predictive values were 100% for MRI and less than or equal to 50% for angiography, CT, and TEE. In all three populations, negative predictive values and accuracies were greater than or equal to 85%. From these results we conclude that diagnostic imaging techniques for aortic dissection do not perform as well in low-risk populations as they do in high-risk populations.
Abstract Background Congestive heart failure (CHF) is a common Emergency Department (ED) disorder that accounts for >5 million ED visits annually. Although quite rare, patent ductus arteriosus (PDA) ...is a serious cause of CHF that if left untreated can lead to life-threatening sequelae, such as hypertensive pulmonary vascular disease, endarteritis, and aneurysms of the ductus. Objective To discuss a case of PDA leading to CHF that illustrates one of the common complications of untreated PDA. Case Report A 35-year-old woman presented to the ED with a 2-month history of shortness of breath, dyspnea on exertion, decreased exercise tolerance, and orthopnea. The physical examination revealed a 4/6 continuous machine-like murmur. In the presence of new CHF and an atypical murmur, a transthoracic echocardiogram was performed that confirmed the diagnosis of PDA. She underwent an uncomplicated percutaneous closure of the ductus with significant improvement in her symptoms. Conclusions Persistent PDA in adulthood is a rare but important cause of CHF with significant morbidity and mortality if not appropriately diagnosed and treated.
This study was designed to test the hypothesis that pulmonary artery pressure at rest and during exercise differs between patients with a transplanted heart and normal subjects and to determine the ...mechanisms responsible for the difference. Twenty-one patients who had undergone heart transplantation 1.5 to 27 months earlier without current evidence of acute cardiac rejection and 25 normal subjects were studied by exercise Doppler echocardiography. Systolic pulmonary artery pressure was higher at baseline in heart transplant patients than in normal subjects, at 31.6 ± 9 mm Hg (mean ± SD) versus 22.5 ± 4, respectively (
p = 0.0001). The increase in systolic pulmonary artery pressure with exercise was 1.4 times higher in heart transplant patients and correlated with pretransplantation pulmonary vascular resistances (
r = 0.55;
p = 0.01). In contrast, cardiac index at baseline or during exercise did not differ between the two groups. Diastolic parameters and ejection fraction at baseline or during exercise did not correlate with systolic pulmonary artery pressure. In conclusion, Doppler exercise echocardiography offers an alternative, safe method hemodynamic study of the transplanted heart. Although an abnormal increase in left ventricular filling pressure with exercise has been well documented, further studies are needed to investigate and characterize potential abnormalities in pulmonary vascular tone in the transplanted heart.
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