A new noninvasive method for evaluation of coronary endothelial function in hypertensive patients based on change in diameter of the left main coronary artery induced by cold pressor test using echocardiography

Endothelial dysfunction in human essential hypertension

Although the endothelium has a number of important functions, the term endothelial dysfunction is commonly used to describe impairment in its vasodilatory capacity. It is increasingly recognized that this is related to hypertension, although whether it predates essential hypertension or is a consequence of it is still unknown. In this review, we explore the mechanisms of endothelial dysfunction in essential hypertension, its prognostic significance and methods of pharmacological reversal.

Vasodilation of epicardial coronary artery can be measured with transthoracic echocardiography

Transthoracic Doppler echocardiography (TTE) has been introduced as a noninvasive tool to measure coronary flow velocity reserve (CFVR). Velocity measurement, however, fails to take into account epicardial coronary artery vasodilation during hyperemia and this may cause underestimation of CFVR measurements. Therefore, we sought to determine whether the vasodilation of epicardial coronary artery can be measured during cold pressor test (CPT) and adenosine infusion simultaneously with the flow velocity measurement using TTE. We studied 41 healthy nonsmoking men with a linear high-frequency 8.0-MHz transducer. The CPT and adenosine infusion dilated the diameter of the distal left anterior descending coronary artery (LAD) from 1.4 +/- 0.4 mm to 1.5 +/- 0.4 mm (14 +/- 13%, p < 0.01) and from 1.4 +/- 0.4 mm to 1.8 +/- 0.5 mm (31 +/- 19%, p < 0.01), respectively. The CPT increased flow velocity and calculated coronary blood flow rate (velocity time integral x cross-sectional area) from 0.23 +/- 0.05 m/s to 0.36 +/- 0.13 m/s (31 +/- 34%, p < 0.01) and from 8.1 +/- 4.2 mL/min to 11.4 +/- 6.0 mL/min (47 +/- 51%, p < 0.01). CFVR and calculated coronary blood flow rate reserve were 3.9 +/- 1.0 and 6.0 +/- 1.9, respectively. In Bland-Altman analysis, velocity measurements underestimated the vasodilation response of the CPT and adenosine compared with the measurements where epicardial diameter dilation was taken into account. Intra- and interobserver variability of diameter measurements was low (coefficient of variation [CV] 2.6 to 6.5%). Day-to-day, within-day and intersonographer variabilities were of similar magnitude (CV 4.6 to 8.2%), suggesting good reproducibility. This study demonstrates that TTE can be used to assess changes in both epicardial coronary artery diameter and flow velocity simultaneously in the distal LAD artery.

Noninvasive assessment of coronary vasodilation using magnetic resonance angiography

OBJECTIVES

The purpose of this study was to investigate the use of coronary magnetic resonance angiography (MRA) for assessing human epicardial coronary artery vasodilation.

BACKGROUND

Coronary vasodilation plays a vital role in the human coronary circulation. Previous studies of epicardial coronary vasodilation have used invasive coronary angiography. Coronary MRA may provide an alternative noninvasive method to directly assess changes in coronary size.

METHODS

Thirty-two subjects were studied: 12 patients (age 55 +/- 18 years) and 20 healthy subjects (age 34 +/- 4 years). High-resolution multi-slice spiral coronary MRA (in-plane resolution of 0.52 to 0.75 mm) was performed before and after sublingual nitroglycerin (NTG). Quantitative analysis of coronary vasodilation was performed on cross-sectional images of the right coronary artery (RCA). A time-course analysis of coronary vasodilation was performed in a subset of eight subjects for 30 min after NTG. Signal-to-noise ratio was also measured on the in-plane RCA images.

RESULTS

Coronary MRA demonstrated a 23% increase in cross-sectional area after NTG (16.9 +/- 7.8 mm2 to 20.8 +/- 8.9 mm2, p <0.0001), with significant vasodilation between 3 and 15 min after NTG on time-course analysis. The MRA measurements had low interobserver variability (< or =5%) and good correlation with X-ray angiography (r=0.98). The magnitude of vasodilation correlated with baseline cross-sectional area (r=0.52, p=0.03) and age (r=0.40, p=0.019). Post-NTG images also demonstrated a 31% improvement in coronary signal-to-noise ratio (p = 0.002).

CONCLUSIONS

Nitroglycerin-enhanced coronary MRA can noninvasively measure coronary artery vasodilation and is a promising noninvasive technique to study coronary vasomotor function.

Value of acceleration flow in the left anterior descending coronary artery for the detection of coronary artery stenosis by transthoracic coronary color Doppler echocardiography

Whether the localized flow acceleration occurs in the resting stenotic left anterior descending coronary artery was explored and its value for detection of coronary stenosis estimated. Blood flow in the left anterior descending coronary arteries in 45 patients was detected by transthoracic color Doppler echocardiograph and multipoint pulse Doppler spectrums were recorded in the same segment. The ratio of the maximal peak diastolic velocity to the minimal peak diastolic velocity was calculated. The ratio > or = 1.5 was the cutoff value for the presence of localized acceleration flow. There were 23 patients with localized acceleration flow examined by echocardiography. Twenty of them were found to have luminal diameter stenosis (60% - 98%) in the left anterior descending coronary arteries by coronary angiography and 3 patients were normal. There were 22 patients without localized acceleration flow examined by echocardiography. Eighteen of them had no or < 60% stenosis. Four patients had serious stenosis (> or = 95%) or occluded segments in the left anterior descending coronary arteries on coronary angiography. The ratio of the maximal peak diastolic velocity to the minimal peak diastolic velocity was significantly higher in patients with left anterior descending coronary artery stenosis than that in those without stenosis (1.9 +/- 0.3 vs 1.3 +/- 0.2, P < 0.01) and it correlated significantly with left anterior descending coronary artery stenosis (r = 0.77, P < 0.01). The specificity by using the ratio > or = 1.5 for stenosis detection was 85.7% (18/ 21), and the sensitivity was 83.3% (20/24). This study demonstrated that local blood flow velocity was increased in the resting stenotic left anterior descending coronary artery. Transthoracic color Doppler echocardiography is a reliable noninvasive method to detect localized acceleration flow in the left anterior descending coronary artery stenosis and it is useful in the noninvasive diagnosis of stenosis in the left anterior descending coronary artery.

Value of echocardiography for evaluation of the flow-dependent epicardial coronary vasodilation in vivo

To assess the value of echocardiography for detection of the flow-dependent epicardial coronary vasodilation, the changes in internal diameter of the left anterior descending coronary arteries (LAD) induced by reactive hyperemia were studied by echocardiography in 12 health anesthetized open-chest dogs. Reactive hyperemia was induced by brief occlusion of the left anterior descending coronary artery for 30 s followed by rapid release. The two- dimensional images of the left anterior descending coronary artery before and after reactive hyperemia with and without intracoronary infusion of N(G)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS) were investigated. The internal diameter of LAD was measured and its percent change induced by reactive hyperemia was calculated. Our results showed that the internal diameter of LAD was 2.23 +/- 0.19 mm before intracoronary infusion of L-NAME (baseline). The internal diameter of LAD significantly increased to 2.52 +/- 0.24 mm (P < 0.01) after reactive hyperemia at baseline, and the percent change in internal diameter of LAD was (13.10 +/- 3.59)%. The internal diameter of LAD before and after reactive hyperemia under the condition of intracoronary infusion of L-NAME was not different from that before reactive hyperemia at baseline. The percent change in internal diameter of LAD was (1.07 +/- 2.97)%, and it was significantly lower than that at baseline (P < 0.001). We are led to conclude that the change in internal diameter of LAD responding to reactive hyperemia was detected sensitively by echocardiography, and this change was associated with endothelium-derived nitric oxide.

Coronary artery diameter can be assessed reliably with transthoracic echocardiography

We studied whether diameters of coronary arteries can be measured accurately with the use of transthoracic echocardiography (TTE). By knowing the anatomic diameter of the coronary artery together with coronary flow velocity it is possible to measure coronary flow volume more precisely by TTE. However, the suitability of TTE for measurement of diameters of all main epicardial coronary arteries has not been systematically validated. We measured the diameters of the left main (LM), left anterior descending (LAD), left circumflex (LCX), and right coronary arteries (RCA) with the use of TTE [manual two-dimensional (2D), color-Doppler, and automated 2D analysis] in 30 patients who had normal coronary anatomy. We compared these diameters to those measured with quantitative coronary angiography (QCA). We could measure diameters of LM, LAD, LCX, and RCA by TTE in up to 37%, 63%, 7%, and 60% of patients, respectively. The overall correlation coefficients between TTE and QCA measurements were 0.83 ( P < 0.01) with manual 2D analysis, 0.82 ( P < 0.01) with automated 2D analysis, and 0.94 ( P < 0.01) with a color-Doppler-based analysis. Interobserver variability of TTE measurements was low (coefficient of variation 5.4 ± 4.6–7.5 ± 8.8%). TTE is an accurate method to evaluate coronary artery diameter in patients with healthy coronary arteries.

Nitric oxide formation contributes to beta-adrenergic dilation of epicardial coronary arteries in response to intravenous administration of dobutamine in dogs

To examine the role of nitric oxide in the beta-adrenergic vasodilation of epicardial coronary arteries in dogs, 12 dogs were instrumented for measurement of left anterior descending coronary artery diameter by transthoracic echocardiography before and after dobutamine (5 microg/kg/min IV) with and without intracoronary infusion of NG-monomethyl-L-arginine (L-NMMA) (1 mg/kg). In all 12 dogs, the diameter of left anterior descending coronary artery increased significantly from 2.35 +/- 0.25 mm to 2.59 +/- 0.24 mm (P<0.001) after dobutamine administration. In 6 of the 12 dogs, the percent change in left anterior descending coronary artery diameter induced by dobutamine decreased significantly from 12.5% +/- 8.6% to -1.5% +/- 5.4% (P<0.05) after the administration of intracoronary L-NMMA (1 mg/kg for 5 min) to block nitric oxide synthesis from L-arginine. The study demonstrated that nitric oxide formation contributes to the beta-adrenergic dilatory response of epicardial coronary arteries to dobutamine in dogs.

Blood pressure in young adulthood and the risk of type 2 diabetes in middle age

OBJECTIVE

Hypertension is known to accompany type 2 diabetes in middle age, but it is unknown how early in life blood pressure (BP) begins to rise among individuals who later develop diabetes. The objective of this study was to evaluate elevated BP as a long-term predictor of type 2 diabetes.

RESEARCH DESIGN AND METHODS

We conducted a prospective cohort study of 1,152 white male medical students in The Johns Hopkins Precursors Study to longitudinally assess systolic BP (SBP) and diastolic BP (DBP) from young adulthood through middle age in men who went on to develop diabetes. Incident diabetes was identified by self-report through mailed questionnaires verified by medical record review.

RESULTS

During a median follow-up of 38 years, 77 cases of incident diabetes occurred. The mean age of diabetes diagnosis was 58 years. As early as age 30 years, mean SBP and DBP were significantly higher in men who developed diabetes during follow-up than in those who remained nondiabetic (SBP 122 vs. 119 mmHg, P = 0.009; DBP 78 vs. 75 mmHg, P = 0.0005). The rate of increase in SBP and DBP over time in men who developed diabetes was greater than the rate of increase in men who did not develop diabetes (SBP 0.49 vs. 0.27 mmHg/year, P < 0.00003; DBP 0.24 vs. 0.17 mmHg/year; P = 0.09). After adjustment for BMI and other risk factors for diabetes, SBP and DBP at age 30 years remained significantly higher in individuals who developed diabetes than in their nondiabetic counterparts; however, the difference in the rate of increase in SBP was no longer significant following multivariate adjustment.

CONCLUSIONS

BP elevations precede the development of type 2 diabetes in middle age by 20-25 years. Higher BP in the prediabetic state might contribute to the presence of vascular disease at the time of diagnosis of type 2 diabetes.

Angiotensin receptor antagonist losartan improves endothelial function of epicardial coronary arteries in patients with essential hypertension

BACKGROUND

Angiotensin II can impair endothelial function, which is mediated by the angiotensin II type 1 receptor subtype.

HYPOTHESIS

The study sought to determine whether treatment with the angiotensin II type 1 receptor antagonist losartan would restore the normal dilation of the left main coronary artery (LMCA) by cold pressor test in patients with essential hypertension, as shown by echocardiography.

METHODS

The study population included 30 patients with mild to moderate essential hypertension and 30 matched healthy subjects. Measurements of the cold pressor test-induced and nitroglycerin-induced changes in LMCA diameter by echocardiography were performed at the end of the washout period and after 12 weeks of losartan administration.

RESULTS

The percent change in LMCA diameter induced by the cold pressor test in hypertensive patients (-3.5 +/- 8.8%) was significantly lower than that in control subjects (10.2 +/- 3.7%, p<0.0001). After losartan treatment, the percent change (13.9 +/- 8.4%) was significantly higher than that before losartan treatment (-3.5 +/- 8.8%, p < 0.0001), but not significandy different between the 17 hypertensive patients with satisfactory control of blood pressure (13.8 +/- 9.1%) and the 13 hypertensive patients without satisfactory control of blood pressure (14.0 +/- 7.7%, p = 0.9). Losartan treatment in patients with essential hypertension did not modify the percent change in LMCA diameter caused by sublingual administration of nitroglycerin (23.2 +/- 14.0% vs. 27.3 +/- 13.7%, p = 0.2).

CONCLUSIONS

This study demonstrates that treatment with losartan normalized response of the LMCA to the cold pressor test in patients with mild to moderate essential hypertension and that this effect is not dependent on the reduction of blood pressure.