Noninvasive quantification of left ventricular wall stress: Validation of method and application to assessment of chronic pressure overload

Abstract

Noninvasive indexes of circumferential wall stress were developed from systolic arterial pressure and echocardiographic left ventricular diameter and thickness (average of septum and posterior wall), applying the basic formula: Stress = (Pressure × Radius)/Wall thickness, where Radius = 1 2 diameter . The radius/wall thickness ratio at end-diastole, end-systole and an average of both (mean systole) were used to calculate three stress indexes: I, II and II) (mean stress), respectively. A very good correlation was observed between each index and peak stress in 25 patients with a variety of valve and myocardial diseases studied during cardiac catheterization (correlation coefficient [r] = 0.82, 0.82 and 0.89 for stress indexes I, II and III, respectively). With use of average normal values for each index as constants, left ventricular systolic pressure was then estimated prospectively in 62 patients with normal left ventricular size and function, 21 (Group A) without and 41 (Group B) with aortic stenosis. In Group A, systolic pressures ranged from 90 to 230 mm Hg and the correlation between estimated and measured pressures was r = 0.92, 0.87, and 0.95 for stress constants I, II and III, respectively. In Group B significant discrepancy (greater than 10 mm Hg, mean 39 mm Hg) between basal arterial pressures at the time of echocardiography and arterial pressures during catheterization was observed in 14 of 41 patients and resulted in a lower, although highly significant (p < 0.001), correlation between estimated and measured left ventricular pressures (r = 0.53, 0.54 and 0.60 for stress constantes I, II and III, respectively) without affecting the correlation between estimated and measured peak aortic valve gradient ( r = 0.78, 0.69 and 0.82 for the respective stress constants). Stress constant III (mean stress), in particular, allowed an accurate separation between patients with gradients above and below 50 mm Hg. Results indicate that peak circumferential wall stress may be accurately estimated noninvasively in a variety of cardiac conditions. The assumption of a stress constant allows assessment of severity of aortic stenosis but only when the pressure stimulus has been chronically sustained and left ventricular cavity size and function remain normal.