Coronary haemodynamics in left ventricular hypertrophy

Considerations in Understanding the Coronary Blood Flow- Left Ventricular Mass Relationship in Patients with Hypertension

Abstract: Background: Coronary blood flow (CBF) is essential for optimal cardiac performance and to maintain myocardial viability. There is considerable ambiguity concerning CBF in hypertension.

Objective: To investigate the relationship between CBF and left ventricular (LV) mass in persons with hypertension.

Methods: OvidSP Medline was systematically searched. Eligible articles assessed CBF, and LV mass in adults with and without hypertension (HTN).

Results: Eleven studies met the entry criteria. All 8 studies reported an increase in CBF (ml/min) for persons with hypertension (N=212) compared to individuals without hypertension (N=150). Meta-analysis showed a significant and 2.88 fold higher CBP in hypertension. Six studies adjusted CBF for LV mass; of which 4 studies reported a reduction in CBF. Meta-analysis showed a significant decrease in CBF/g LV mass in hypertension. The two studies that did not show a decrease in CBF, used the argon chromatographic method to measure coronary sinus blood flow suggesting this methodology may have influenced the results. Using the mean CBF in normotensive group to construct the expected CBF according to LV mass, reported CBF in HTN was progressively less than expected In two studies, (N=142), there was a significant inverse correlation between LV mass and CBF/ g LV mass. Multivariate analysis (three studies) consistently found a highly significant independent relationship between LV mass and CBF after considering age, sex, heart rate and several other factors.

Conclusion: Hypertension is associated with a reduction in CBF adjusted for LV mass with a highly significant inverse association between CBF and LV mass. Clinicians should be aware that patients with hypertension are at greater risk for myocardial ischemia should develop other factors that limit CBF or myocardial oxygen delivery.

Hypertension and coronary artery disease: epidemiology, physiology, effects of treatment, and recommendations : A joint scientific statement from the Austrian Society of Cardiology and the Austrian Society of Hypertension

High blood pressure is a major modifiable risk factor for all clinical manifestations of coronary artery disease (CAD). In people without known cardiovascular disease, the lowest systolic (down to 90-114 mmHg) and the lowest diastolic (down to 60-74 mmHg) pressures are associated with the lowest risk for developing CAD. Although diastolic blood pressure is the strongest predictor of CAD in younger and middle-aged people, this relationship becomes inverted and pulse pressure shows the strongest direct relationship with CAD in people above 60 years of age.Pathophysiological mechanisms of blood pressure as a risk factor for CAD are complex and include the influence of blood pressure as a physical force on the development of the atherosclerotic plaque, and the relationship between pulsatile hemodynamics/arterial stiffness and coronary perfusion. Treatment of arterial hypertension has been proven to prevent coronary events in patients without clinical CAD. In patients with established CAD, the effect of blood pressure lowering per se is beneficial, probably more than specific drugs or drug classes. The important exceptions are beta blockers (BBs), which are superior to all other drug classes for use after a recent myocardial infarction. Blood pressure targets in patients with established CAD have created controversy in the light of the so-called J-curve phenomenon, which describes an increase in coronary events at lower diastolic blood pressures. One explanation for this observation is that perfusion of the left ventricle occurs predominantly during diastole, and that coronary autoregulation may be exhausted with low diastolic blood pressure in the setting of left ventricular hypertrophy and atherosclerotic narrowing of the epicardial coronaries. The worst situation is a high systolic blood pressure in the presence of a low diastolic blood pressure, both a hallmark of increased aortic stiffness. However, the lowering of systolic blood pressure is clearly beneficial in this setting, even at the price of further lowering diastolic pressure. Primary blood pressure goal in patients with established CAD is below 140/90 mmHg. Recent studies suggest that a lower systolic blood pressure may be appropriate, whereas caution is advised with diastolic blood pressure below 60 mmHg.

Measurement of technetium-99m sestamibi signals in rats administered a mitochondrial uncoupler and in a rat model of heart failure

Background

Many methods have been used to assess mitochondrial function. Technetium-99m sestamibi (^99mTc-MIBI), a lipophilic cation, is rapidly incorporated into myocardial cells by diffusion and mainly localizes to the mitochondria. The purpose of this study was to investigate whether measurement of ^99mTc-MIBI signals in animal models could be used as a tool to quantify mitochondrial membrane potential at the organ level.

Methods and Results

We analyzed ^99mTc-MIBI signals in Sprague-Dawley (SD) rat hearts perfused with carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler known to reduce the mitochondrial membrane potential. ^99mTc-MIBI signals could be used to detect changes in the mitochondrial membrane potential with sensitivity comparable to that obtained by two-photon laser microscopy with the cationic probe tetramethylrhodamine ethyl ester (TMRE). We also measured ^99mTc-MIBI signals in the hearts of SD rats administered CCCP (4 mg/kg intraperitoneally) or vehicle. ^99mTc-MIBI signals decreased in rat hearts administered CCCP, and the ATP content, as measured by ³¹P magnetic resonance spectroscopy, decreased simultaneously. Next, we administered ^99mTc-MIBI to Dahl salt-sensitive rats fed a high-salt diet, which leads to hypertension and heart failure. The ^99mTc-MIBI signal per heart tissue weight was inversely correlated with heart weight, cardiac function, and the expression of atrial natriuretic factor, a marker of heart failure, and positively correlated with the accumulation of labeled fatty acid analog. The ^99mTc-MIBI signal per liver tissue weight was lower than that per heart tissue weight.

Conclusion

Measurement of ^99mTc-MIBI signals can be an effective tool for semiquantitative investigation of cardiac mitochondrial membrane potential in the SD rat model by using a chemical to decrease the mitochondrial membrane potential. The ^99mTc-MIBI signal per heart tissue weight was inversely correlated with the severity of heart failure in the Dahl rat model.

Setting the stage

Intradialytic hypotension (IDH) occurs during 25% to 50% of end-stage renal disease (ESRD) hemodialysis (HD) treatments. The development of IDH signals both technology- and patient-dependent limitations expressed across a broad range of symptoms, from nausea and muscle cramps to ischemic injury. While traditional thinking has emphasized the link between hypertension and cardio-cerebrovascular injury, more recent studies of ESRD patients have stimulated significant interest in hypotension and poor outcomes. Theoretically, hypotension can contribute to the increased relative risk of death in ESRD by several mechanisms, which include acute coronary syndrome, autoregulation dysfunction, ischemia, and arrhythmogenicity. Endothelial abnormalities (increased procoagulation, thrombogenecity risk, and alterations in coronary flow reserve) and altered vascular distribution within the myocardium provide an environment for vascular injury. The current symposia will examine the pathophysiology of IDH, the specific HD prescription modifications to prevent IDH, and newer pharmacologic interventions to treat IDH and will highlight the approach to several clinical cases based on the information presented. It is becoming increasingly important to identify patients at "high risk" for IDH, to customize the HD prescription to the individual patient, to use drug therapy to prevent IDH events, and to track the prevalence of chronic hypotension and the incidence of IDH complications in the dialysis unit.

Myocardial bridging as a cause of acute transient left heart dysfunction

The significance of myocardial bridging is still a matter of debate, and although several reports have underlined its pathologic potential, myocardial bridging is often considered to be a benign phenomenon. We present here the case of a 63-year-old woman with a history of acute left heart failure and ECG evidence of ischemia, and whose primary abnormality on extensive workup was myocardial bridging. This case further underlines that myocardial bridging can lead to significant cardiac events.

Hypertension and coronary artery disease

Hypertension is one of the major risk factors for coronary artery disease. This risk is considerably magnified by the presence of left ventricular hypertrophy. The likeliest dominant factor in this increased risk is myocardial ischaemia, the recognition of which is of key importance. Antihypertensive agents ideally should also protect against occurrence of the clinical syndromes associated with coronary artery disease.