Lowering of blood pressure and coronary blood flow in isolated systolic hypertension

Is Peri-Operative Isolated Systolic Hypertension (ISH) a Cardiac Risk Factor?

We are presenting a review of Isolated Systolic Hypertension (ISH) as a cardiovascular risk factor with emphasis on the perioperative period.

Isolated systolic hypertension is associated with aging and is the most frequent subtype (65%) among patients with uncontrolled hypertension. ISH is strongly associated with increased risks of cardiac and cerebrovascular events exceeding those in comparably aged individuals with diastolic hypertension. Patients with ISH show an increase in left ventricular (LV) mass and an increase in the prevalence of left ventricular hypertrophy (LVH). These LV changes increase cardiovascular events and frequently lead to diastolic dysfunction (DD). Treatment to reduce elevated systolic blood pressure has been shown to reduce the risk of cardiovascular events.

In the perioperative setting, essential hypertension has not been found to be a significant risk factor for cardiac complications. Most of the studies were based on the definition of essential hypertension and underpowered in sample size. The significance of perioperative ISH, however, is not well studied, partly due to its recognition only fairly recently as a cardiovascular risk factor in the non-surgical setting, and partly due to the evolving definition of ISH.

Perioperative cardiac complications remain a significant problem to the healthcare system and to the patient. Although the incidence of perioperative cardiac complications is prominent in high-risk patients as defined by the Revised Cardiac Risk Index (RCRI), the bulk of the cardiac complications actually occur in low-risk group. Currently, little understanding exists on the occurrence of perioperative cardiac complications in low- risk patients. A factor such as ISH, with its known pathophysiological changes, is a potential perioperative risk factor.

We believe ISH is an under-recognized perioperative risk factor and deserves further studying. Our research group has recently been funded by the Heart Stroke Foundation (HSF) to examine ISH as a perioperative risk factor (PROMISE Study).

Perioperative control of hypertension: when will it adversely affect perioperative outcome?

Much has been published about the impact of treatment on adverse outcomes in patients with cardiovascular diseases. Hypertension is an extremely common condition affecting a significant percentage of the world population. Although care guidelines exist for the medical patient with raised blood pressure, there are no accepted guidelines for the preoperative evaluation and perioperative care of the patient with hypertension who undergoes noncardiac surgery. Of particular importance are defining at-risk groups of patients, and the indications for cancellation to treat and hence reduce this risk. This review examines the interactions between hypertension, drug therapies, anesthesia, and adverse outcomes in these patients. Recommendations for identifying patients at greatest risk of adverse cardiovascular events and cardiac mortality have been developed through evaluation of available data. Based on these findings, the only patients in whom cancellation may be justified and the level of hypertension treated prior to surgery are those with stage 2 hypertension and accompanying target-organ damage, or stage 3 hypertension (blood pressure > 180/> 110 mm Hg).

Cross-Talk Between Cardiac Muscle and Coronary Vasculature

The cardiac muscle and the coronary vasculature are in close proximity to each other, and a two-way interaction, called cross-talk, exists. Here we focus on the mechanical aspects of cross-talk including the role of the extracellular matrix. Cardiac muscle affects the coronary vasculature. In diastole, the effect of the cardiac muscle on the coronary vasculature depends on the (changes in) muscle length but appears to be small. In systole, coronary artery inflow is impeded, or even reversed, and venous outflow is augmented. These systolic effects are explained by two mechanisms. The waterfall model and the intramyocardial pump model are based on an intramyocardial pressure, assumed to be proportional to ventricular pressure. They explain the global effects of contraction on coronary flow and the effects of contraction in the layers of the heart wall. The varying elastance model, the muscle shortening and thickening model, and the vascular deformation model are based on direct contact between muscles and vessels. They predict global effects as well as differences on flow in layers and flow heterogeneity due to contraction. The relative contributions of these two mechanisms depend on the wall layer (epi- or endocardial) and type of contraction (isovolumic or shortening). Intramyocardial pressure results from (local) muscle contraction and to what extent the interstitial cavity contracts isovolumically. This explains why small arterioles and venules do not collapse in systole. Coronary vasculature affects the cardiac muscle. In diastole, at physiological ventricular volumes, an increase in coronary perfusion pressure increases ventricular stiffness, but the effect is small. In systole, there are two mechanisms by which coronary perfusion affects cardiac contractility. Increased perfusion pressure increases microvascular volume, thereby opening stretch-activated ion channels, resulting in an increased intracellular Ca2+transient, which is followed by an increase in Ca2+sensitivity and higher muscle contractility (Gregg effect). Thickening of the shortening cardiac muscle takes place at the expense of the vascular volume, which causes build-up of intracellular pressure. The intracellular pressure counteracts the tension generated by the contractile apparatus, leading to lower net force. Therefore, cardiac muscle contraction is augmented when vascular emptying is facilitated. During autoregulation, the microvasculature is protected against volume changes, and the Gregg effect is negligible. However, the effect is present in the right ventricle, as well as in pathological conditions with ineffective autoregulation. The beneficial effect of vascular emptying may be reduced in the presence of a stenosis. Thus cardiac contraction affects vascular diameters thereby reducing coronary inflow and enhancing venous outflow. Emptying of the vasculature, however, enhances muscle contraction. The extracellular matrix exerts its effect mainly on cardiac properties rather than on the cross-talk between cardiac muscle and coronary circulation.

Hemodynamic, hemostatic, and endothelial reactions to psychological and physical stress in coronary artery disease patients

Episodes of psychological and physical stress may elicit thrombotic cardiac events, such as myocardial infarction. These events are triggered when there are concurrent hemodynamic, hemostatic, and endothelial abnormalities. Hemodynamic, hemostatic, and endothelial reactions of 72 (15 women, 57 men) coronary artery disease patients to psychological and physical stress were examined. Blood pressure, electrocardiography, and impedance cardiography were recorded during rest, mental arithmetic, and exercise. Blood was collected, via catheter, at rest and after each task. Mental arithmetic elicited increases in blood pressure, heart rate, cardiac output, and cardiac contractility, but no consistent changes in hemostatic and endothelial markers. In contrast, exercise, in addition to increasing blood pressure, heart rate, cardiac output, cardiac contractility, and lowering peripheral resistance, elicited increases in plasma viscosity, hematocrit, platelets, and tissue plasminogen activator together with a decrease in plasminogen activator inhibitor. This pattern of hemodynamic, hemostatic, and endothelial reactions suggests that acute psychological and physical stress influence the thrombotic system differently in these high risk patients. Future research is needed to investigate how these stress responses are prospectively related to acute cardiac events.

Anaesthesia and isolated systolic hypertension--pathophysiology and anaesthesia risk

This review examines the pathophysiology of isolated systolic hypertension, changing medical perspectives on this condition as a cardiovascular risk factor in the community and evolving evidence of it being an independent risk factor for perioperative morbidity and mortality. Hypertension is regarded as an added risk in anaesthesia. Continuation of antihypertensive medication through the perioperative period is an established principle. Studies supporting this practice have demonstrated greater perioperative haemodynamic stability in association with general anaesthesia and surgery in patients with treated hypertension compared to untreated hypertension. Therapy has historically focused on control of diastolic blood pressure, rather than systolic blood pressure. Recent clinical trial data and data from large observational studies show a closer association of systolic hypertension with both coronary heart disease and stroke compared with diastolic hypertension. This has led to recommendations for aggressive treatment of isolated systolic hypertension, especially in patients over 65 years old. The association between decreased compliance of the central systemic arteries and isolated systolic hypertension is well understood. The fact that this same pathology, lack of compliance of central arteries, can cause a decrease in diastolic blood pressure is not so well recognised. This means that, in patients with isolated systolic hypertension, decreasing diastolic blood pressure can be associated with worsening arterial disease and that systolic minus diastolic blood pressure may give a better indication of the problem. Anaesthetic assessment and technique should be studied and potentially revised in the light of these changes in perspective on isolated systolic hypertension.