Coronary microcirculation in essential hypertension: a quantitative myocardial contrast echocardiographic approach

Usefulness of Stress-Derived E/e' Ratio in Asymptomatic Hypertensive Patients

Purpose

We sought to investigate the usefulness of stress echocardiography-derived E/e' in predicting subclinical atherosclerosis in asymptomatic hypertensive patients.

Materials and Methods

71 newly diagnosed untreated hypertensive patients (48 ± 13 years, 65% males) and 30 age- and sex-matched healthy controls were recruited. Resting and exercise echocardiography was performed to assess resting diastolic blood pressure and the diastolic stress parameters. Coronary flow reserve (CFR) was evaluated as well.

Results

Based on CFR values, newly diagnosed, untreated hypertensives were stratified into hypertensives with microvascular dysfunction (MVD; 34 patients had CFR <2.0) and those without MVD (37 patients had CFR ≥2.0). Patients with MVD had a significantly higher C-reactive protein level (p < 0.05) and lower metabolic equivalent values (p < 0.05). With resting echocardiography, only the left atrial volume index (LAVI) was significantly increased in those with MVD compared with those without MVD and controls (p < 0.05). With exercise echo, the E/e' was significantly increased in MVD patients compared with those without MVD and controls (p < 0.001). Importantly, the percentage of subjects with exercise E/e' ≥15 was 76.5% (26 patients in the group with MVD), 4.1% (3 patients in the group without MVD), and 0% in controls. At univariate analysis, high-sensitivity C-reactive protein (p < 0.05), LAVI (p < 0.05), and exercise E/e' (p < 0.001) were independently associated with reduced CFR. On the other hand, at multivariate analysis, only exercise E/e' was the independent predictor of reduced CFR in newly diagnosed hypertensives.

Conclusion

We have demonstrated significant associations between exercise-derived raised left ventricular pressure and coronary MVD in newly diagnosed untreated hypertensive patients. Herein, we supposed that exercise-derived E/e' could predict subclinical atherosclerosis and might be a risk parameter for newly diagnosed untreated hypertensive patients.

Hypertension, Left Ventricular Hypertrophy, and Myocardial Ischemia

The risks associated with hypertension emerge through a series of complex interactions. Myocardial ischemia is the major contributor to this risk. The mechanisms driving ischemia reflect many of the key factors in hypertension, including endothelial and neurohumoral factors, fibrosis, and hemodynamics. Left ventricular hypertrophy and fibrosis are of fundamental importance and together with hemodynamics provide an optimal template for myocardial ischemia. Understanding the pathophysiology has aided a more rational management approach but challenges remain which, if surmounted, will have an impact on the morbidity and mortality caused by myocardial ischemia in patients with hypertension.

Prognostic value of exercise-induced left ventricular systolic dysfunction in hypertensive patients without coronary artery disease

INTRODUCTION AND OBJECTIVES

We sought to assess the prognostic value of exercise-induced left ventricular systolic dysfunction in hypertensive patients with normal resting echocardiography and absence of coronary artery disease.

METHODS

From our database of patients referred for treadmill exercise echocardiography, we identified 93 hypertensive patients with preserved resting left ventricular ejection fraction (≥ 50%), no evidence of structural heart disease, and absence of coronary artery disease on angiography. Overall, 39 patients developed exercise-induced left ventricular systolic dysfunction (defined as a decrease in left ventricular ejection fraction below 50% at peak exercise) and 54 exhibited a normal left ventricular ejection fraction response to exercise. The mean follow-up was 6.1 (3.7) years. End points were all-cause mortality, cardiac death, heart failure, and the composite event of cardiac death or heart failure.

RESULTS

Patients who developed exercise-induced left ventricular systolic dysfunction were at higher risk of death from any cause (hazard ratio=3.4; 95% confidence interval, 1.1-10.3), cardiac death (hazard ratio=5.6; 95%CI, 1.1-29.4), heart failure (hazard ratio=8.9; 95% confidence interval, 1.8-44.2), and the composite end point (hazard ratio=5.7; 95% confidence interval, 1.7-19.0). In the multivariate analysis, exercise-induced left ventricular systolic dysfunction remained an independent predictor of both heart failure (hazard ratio=6.9; 95% CI, 1.3-37.4) and the composite event of cardiac death or heart failure (hazard ratio=4.5; 95% confidence interval, 1.2-16.0).

CONCLUSIONS

In hypertensive patients with preserved resting left ventricular ejection fraction and absence of coronary artery disease, exercise-induced left ventricular systolic dysfunction is a strong predictor of cardiac events and may represent early hypertensive heart disease.

Hypertension and myocardial ischemia

Detailed studies over the past 30 years have built up an impressive evidence base for the presence of myocardial ischemia in patients who have hypertension. This relationship ranges from the obvious association with obstructive coronary artery disease to mechanisms related to hemodynamic, microcirculatory, and neuroendocrine abnormalities. All of these factors serve to destabilize the critical balance between myocardial oxygen supply and demand. We have at our disposal a range of sophisticated investigations that allow us to demonstrate the presence and extent of the ischemia and therefore to target specific therapies to reduce the risk to these patients. Achieving target BP and managing all reversible components of the patient's cardiovascular risk status reduce to a minimum the clinical sequelae of myocardial ischemia in this vulnerable population..

From hypertension to heart failure: role of nitric oxide-mediated endothelial dysfunction and emerging insights from myocardial contrast echocardiography

There is growing evidence that nitric oxide (NO)-mediated endothelial dysfunction occurs in hypertension and may represent the earliest stage of target organ damage, which ultimately leads to hypertensive heart disease and heart failure (HF). An understanding of how impaired myocardial microvascular function and flow reserve relate to early remodeling during the transition to HF in patients with hypertension may lead to new therapeutic insights. The hypertrophied heart, which is a feature of the adverse structural remodeling in hypertensive heart disease, may be accompanied by impaired coronary flow reserve (CFR). Reduced CFR could potentially cause subendocardial ischemia during conditions of high metabolic demand, such as uncontrolled hypertension and tachycardia. Such vulnerability of the subendocardium to abnormal perfusion or ischemia may accelerate the progression from compensated hypertrophy to HF. In this review, we discuss preliminary evidence that altered NO balance may contribute to cardiac hypertrophy-mediated myocardial ischemia. We also describe early results with myocardial contrast echocardiography in the postulated transition from compensated hypertrophy to cardiac failure. These data support further evaluation of NO mediators as potential targets for novel therapies in hypertensive heart disease.

Effect of one or more co-morbid conditions on diagnostic accuracy of coronary flow velocity reserve for detecting significant left anterior descending coronary stenosis

OBJECTIVE

To determine the effect of one or multiple co-morbid conditions on the diagnostic accuracy of coronary flow velocity reserve (CFVR) in a heterogeneous patient population.

METHODS

CFVR was measured in the left anterior descending coronary artery (LAD) by transthoracic Doppler echocardiography (TTDE) in 318 consecutive patients before elective coronary angiography. CFVR was calculated as the average peak diastolic velocity during intravenous ATP infusion divided by baseline flow velocity. All patients underwent coronary angiography within 48 hours. Significant LAD stenosis was defined as > 50% luminal narrowing. Diagnostic accuracy of CFVR was analysed according to the type and number of risk factors that may adversely affect microvascular function.

RESULTS

CFVR was measured in 309 patients, of whom 105 were found to have significant LAD stenosis based on coronary angiography. CFVR < 2.0 had a sensitivity of 86% and a specificity of 77% for predicting significant LAD stenosis. Left ventricular hypertrophy (LVH) was the only factor that significantly lowered diagnostic accuracy (61% with LVH v 84% without LVH, p < 0.001). Diagnostic accuracy was not affected by increasing number of risk factors.

CONCLUSIONS

The diagnostic accuracy of CFVR by TTDE for detecting significant LAD stenosis remains high in a more clinically relevant population with multiple cardiovascular co-morbidities. Only the presence of LVH adversely affected diagnostic accuracy.

Loss of endothelial KATP channel-dependent, NO-mediated dilation of endocardial resistance coronary arteries in pigs with left ventricular hypertrophy

The influence of left ventricular hypertrophy (LVH) on the endothelial function of resistance endocardial arteries is not well established. The aim of this study was to characterise the mechanisms responsible for UK-14,304 (alpha(2)-adrenoreceptor agonist)-induced endothelium-dependent dilation in pig endocardial arteries isolated from hearts with or without LVH. LVH was induced by aortic banding 2 months before determining endothelial function. Following euthanasia, hearts were harvested and endocardial resistance arteries were isolated and pressurised to 100 mmHg in no-flow conditions. Vessels were preconstricted with acetylcholine (ACh) or high external K(+) (40 mmol l(-1) KCl). Results are expressed as mean+/-s.e.m. UK-14,304 induced a maximal dilation representing 79+/-6% (n=8) of the maximal diameter. NO synthase (l-NNA, 10 micromol l(-1), n=7) or guanylate cyclase (ODQ, 10 micromol l(-1), n=4) inhibition reduced (P<0.05) UK-14,304-dependent dilation to 35+/-6 and 18+/-7%, respectively. Apamin and charybdotoxin reduced (P<0.05) to 39+/-8% (n=4) the dilation induced by UK-14,304. In depolarised conditions, however, this dilation was prevented (P<0.05). UK-14,304-induced dilation was reduced (P<0.05) by glibenclamide (Glib, 1 micromol l(-1)), a K(ATP) channel blocker, either alone (35+/-10%, n=5) or in combination with l-NNA (34+/-9%, n=4). In LVH, UK-14,304-induced maximal dilation was markedly reduced (25+/-4%, P<0.05) compared to control; it was insensitive to l-NNA (21+/-5%) but prevented either by the combination of l-NNA, apamin and charybdotoxin, or by 40 mmol l(-1) KCl. Activation of endothelial alpha(2)-adrenoreceptor induces an endothelium-dependent dilation of pig endocardial resistance arteries. This dilation is in part dependent on NO, the release of which appears to be dependent on the activation of endothelial K(ATP) channels. This mechanism is blunted in LVH, leading to a profound reduction in UK-14,304-dependent dilation.

Tracking of regions-of-interest in myocardial contrast echocardiography

Analysis of intramyocardial perfusion by contrast echocardiography provides quantitative parameters for the assessment of ischemic disease. This analysis can be achieved by applying an ultrasound (US) burst of high mechanical index to destroy contrast bubbles, measuring various myocardial refilling parameters from the time curves obtained from regions-of-interest (ROIs) within the myocardial wall. To obtain reliable intensity curves, the position of the ROIs must be tracked to compensate for the heart motion along the sequence. In this work, we studied the use of optical flow techniques for ROI repositioning. Two block-matching and one differential technique were evaluated for this purpose. Performance was measured by comparing the result of automatic tracking with results of ROI repositioning by a human expert. This evaluation was carried out on experimental data from animals as well as on sequences from clinical studies. Results are considered to be accurate enough for clinical purposes, and computation times may allow for a real-time processing if incorporated into a US scanner.