Excess Pressure Integral Predicts Cardiovascular Events Independent of Other Risk Factors in the Conduit Artery Functional Evaluation Substudy of Anglo-Scandinavian Cardiac Outcomes Trial

Abstract

S ystolic and diastolic blood pressure (BP) are important modifiable risk factors for cardiovascular disease.1 Recently, there has been increased interest in the potential predictive value of other parameters derived from the BP waveform. The complex interactions between the heart and the arterial system cause distinctive changes in the BP waveform with aging and disease. Two basic concepts have been advanced to explain these changes: windkessel models and wave transmission models. Windkessel models describe the pressure waveform in terms of a compliant elastic arterial component coupled to an outflow resistance corresponding to the microcirculation. This is a simple and intuitive model of the circulation, but its limitations in systole are well recognized. This approach has been supplanted largely by models based on arterial wave travel.2,3 Westerhof et al 4 devised a method for the separation of arterial waves into their forward and backward traveling components, but the original approach requires the simultaneous measurement of arterial pressure and flow at the same location, which is difficult to perform noninvasively. Studies using proxies for wave reflection, such as central augmentation index (AIx), have not consistently shown associations with major adverse cardiovascular events, 5-8 and a recent metaanalysis 9 found that although increased AIx was associated with increased risk of cardiovascular events overall, there was significant heterogeneity between studies. Recently, we suggested that Abstract-Excess pressure integral (XSPI), a new index of surplus work performed by the left ventricle, can be calculated from blood pressure waveforms and may indicate circulatory dysfunction. We investigated whether XSPI predicted future cardiovascular events and target organ damage in treated hypertensive individuals. Radial blood pressure waveforms were acquired by tonometry in 2069 individuals (aged, 63±8 years) in the Conduit Artery Functional Evaluation (CAFE) substudy of the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT). Measurements of left ventricular mass index (n=862) and common carotid artery intima media thickness (n=923) were also performed. XSPI and the integral of reservoir pressure were lower in people treated with amlodipine±perindopril than in those treated with atenolol±bendroflumethiazide, although brachial systolic blood pressure was similar. A total of 134 cardiovascular events accrued during a median 3.4 years of follow-up; XSPI was a significant predictor of cardiovascular events after adjustment for age and sex, and

Aortic Reservoir Pressure Corresponds to Cyclic Changes in Aortic Volume

“…Indeed, such evidence was recently reported from the Conduit Artery Function Evaluation study, where excess pressure integral was shown to independently predict cardiovascular events. 10 The excess pressure waveform has also been consistently shown to bear striking resemblance to the flow velocity trace in the ascending aorta, 6,7,11,17 representative of LV stroke volume. 20 With regard to Figure 2, it is XP derived that first rapidly rises with aortic pressure, before AR direct and RP derived (ie, reservoir pressure) more gradually begin to increase as the aorta distends and volume increases.…”

“…6,8 Moreover, indices derived from this model were recently shown to predict cardiovascular events (fatal and nonfatal) and procedures independent from brachial BP and other conventional cardiovascular risk parameters (eg, age, sex, cholesterol, smoking, diabetes mellitus), including Framingham risk score, in an analysis of the Conduit Artery Function Evaluation study. 10 In accounting for the reservoir function of the aorta, 7,11 the reservoir-excess pressure model is founded on the basis that aortic BP can be separated into…”

Evaluation of Arterial Stiffness in Patients with Bronchial Asthma and Co-Existent Chronic Obstructive Pulmonary Disease

“…The results of the Conduit Artery Function Evaluation (CAFE) study, a substudy of the Anglo-Scandinavian Cardiac Outcomes Trial (ASCOT) have confirmed that central aortic pressure is a stronger predictor of stroke and CHD complications as compared to peripheral blood pressure (BP) in the brachial artery [31].…”

Practical Suitability of a Stand-Alone Oscillometric Central Blood Pressure Monitor: A Review of the Microlife WatchBP Office Central

“…This leads to augmented BP and results in left ventricular hypertrophy due to the increased myocardial load. The reservoir pressure is highly correlated with changes in proximal aortic volume, and parameters from the reservoir wave can predict cardiovascular events and correlates with left ventricular mass [40,41,42]. The excess pressure integral is the difference between the measured BP waveform and reservoir pressure, and is a measure of the extra work needed by the left ventricle.…”