Diagnostic Methods Valvuiar Heart Disease

We describe a noninvasive method for determining end-systolic meridional and circumferential wall stress and left ventricular architecture as the ratio of muscle to cavity area. With this technique, which uses two-dimensional echocardiography and cuff-determined values for systolic blood pressure, we assessed wall stress and left ventricular architecture in 15 normal subjects and 15 asymptomatic patients with severe chronic aortic regurgitation at rest and after load manipulations with sublingual nitroglycerin. Resting end-systolic meridional and circumferential stress were increased in patients with aortic regurgitation (113.9 + 29 and 260 + 50.7 x l0 dynes/em2) compared with those in normal subjects (85.6 + 15.4 and 214.1 ± 28.4 x 10 dynes/cm2) (both p < .01) and remained significantly greater after nitroglycerin. Meridional stress values obtained from two-dimensional echocardiographic studies correlated closely (r = . 89) with values calculated from simultaneously recorded M mode echocardiograms. Ejection fraction in patients with aortic regurgitation and normal subjects were similar at rest (55 ± 10% vs 59 + 6%) and were unchanged by nitroglycerin. In spite of the increased left ventricular mass in patients with aortic regurgitation (227 ± 60 g vs 130 22 g in normal subjects), the mass-to-volume ratio and the ratio of muscle to cavity area in diastole in patients with aortic regurgitation were significantly lower than normal (0.90 + 0.23 vs 1.30 ± 0.21 and 0.91 + 0.23 vs 1.11 ± 0.18 [p < .005 and p < .02]). These differences were exaggerated after nitroglycerin, while concomitant changes in relative wall thickness were virtually undetected by M mode echocardiography. Thus this technique can be used for early recognition of afterload excess and changes in left ventricular architecture in patients with aortic regurgitation. Furthermore, the mean slopes of the circumferential stress-diameter and meridional stress-length lines, which represent load-independent indexes of myocardial contractile state, could be assessed and were similar in the group of patients with asymptomatic aortic regurgitation and normal subjects, indicating that overall myocardial contractility was still normal. We conclude that circumferential and meridional wall stress, myocardial contractility, and left ventricular architecture can be determined noninvasively. These measurements may prove to be useful in assessing patients with primary myocardial or valvular heart disease and determining their long-term management. Circulation 69, No. 2, 259-268, 1984. END-SYSTOLIC meridional stress, which can be evaluated by M mode echocardiography, is a readily determined quantitative index of left ventricular afterload and may have clinical and therapeutic implications." 2 The relationship between meridional stress and left ventricular diameter may be an important loadindependent index of myocardial contractile state.' Relative wall thickness measured by M mode echocardiography has also been a useful descriptor of left From the Cardiovascular Section, Hospital of the University of Pennsylvania, Philadelphia. Address for correspondence: Martin G. St. John Sutton, M.D., Room 959 Gates, Cardiovascular Section, Hospital of the University of Pennsylvania, Philadelphia, PA 19104. Received Aug. 1, 1983; revision accepted Oct. 13, 1983. Vol. 69, No. 2, February 1984 ventricular short-axis architecture.5 However, there are potential limitations to the use ofM mode echocardiography to measure left ventricular diameter and wall thickness. Among these are included the following: (1) there is a possibility of variability in repetitive measurements of left ventricular diameter and wall thickness, which is of special concern in patients with enlarged hearts6; small changes in measurements of diameter and particularly of wall thickness could result in large discrepancies in left ventricular end-systolic wall stress. (2) The cross section of the left ventricle imaged by M mode echocardiography, the so-called ice pick view, is assumed to be representative of the left ventricle as a whole, and the presence of segmental 259 by gest on A ril 3, 2017 http://ciajournals.org/ D ow nladed from ST. JOHN SUTTON et al. wall motion abnormalities, which would invalidate wall stress calculations, cannot be reliably excluded. (3) Because M mode echocardiography cannot measure the left ventricular long axis, no attempt can be made to assess circumferential stress, which is of much greater magnitude than meridional stress and may have a closer relationship to left ventricular emptying and ejection fraction. Strictly speaking, plots of end-systolic stress diameters should relate circumferential stress to left ventricular diameter, and meridional stress to ventricular length. We therefore devised a new noninvasive method of determining relative wall thickness, end-systolic meridional stress, and end-systolic circumferential stress by means of two-dimensional echocardiography, which may circumvent the important shortcomings ofM mode echocardiographic tech-