Interventricular septal and free wall dynamics in hypertrophic cardiomyopathy

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Interventricular Septal and Free Wall Dynamics in Hypertrophic Cardiomyopathy SANJIV KAUL, MD, CHUWA TEl, MD, FACC, PRAVIN M. SHAH, MD, FACC Los Angeles, California

Two-dimensional echocardiography was used to analyze interventricular septal and free wall dynamics in eight normal subjects and eight patients with hypertrophic cardiomyopathy. Upper, middle and lower septal and corresponding free wall motion and thickening were analyzed using both fixed and floating reference systems. The lower and midseptal dynamics did not seem to differ significantly between the two groups and the lower septum seemed to move more than the corresponding free wall (probability [pI < 0.05). The upper septum moved

Earlier studies (1,2) have described the interventricular septum as being hypokinetic or adynamic in hypertrophic cardiomyopathy. These studies utilized M-mode echocardiography to evaluate septal motion and thickening. Subsequent reports utilizing the same technique have reinforced this observation (3-5), and the notion that the septum in hypertrophic cardiomyopathy thickens and moves poorly is commonly held (6-8). There is an implied relation of the pronounced myofiber disarray commonly observed in the interventricular septum with the reported hypokinesia. Because preliminary observations in our laboratory with two-dimensional echocardiography using multiple cross sections failed to show the interventricular septum to be adynamic in subjects with hypertrophic cardiomyopathy, a systematic analysis of septal motion in these subjects and in normal subjects was carried out. The present report will show that the interventricular septum in hypertrophic cardioFrom the Department of Medicme , University of Califorma School of Medicine, Wadsworth Veterans Adminrstration Medical Center, Los Angeles, California. This work was supported in part by The Arthur Dodd Fuller Foundation for Cardio-Vascular Research, Los Angeles, California and Medical Research funds from the Veterans Administration, Washington, D.C. Dr. Chuwa Tei is a Senior Investigator of the American Heart Association, Greater Los Angeles Affiliate, Los Angeles, California, supported in part by GroupInvestigatorship Award. Manuscript received July 19, 1982; revised manuscript received November 16, 1982, accepted November 19, 1982. Address for reprints. Pravin M. Shah, MD, Cardiology (691/llIE), Wadsworth Veterans Administration Medical Center, Wilshire and Sawtelle Boulevards, Los Angeles, California 90073. © 1983 by the Amencan College of Cardiology

and thickened less than the rest of the septum in both groups (p < 0.05), but was less dynamic in patients with hypertrophic cardiomyopathy than in normal subjects when the fixed reference system was used (p < 0.05). It is concluded that the interventricular septum in hypertrophic cardiomyopathy is not akinetic. Previously reported hypokinesia of the septum in hypertrophic cardiomyopathy may be due to sampling of the upper septum by M-mode echocardiography and to the fixed system of reference used by M-mode echocardiography.

myopathy, far from being hypokinetic or adynamic, exhibits normal or increased excursion during systole.

Methods Patient selection. Eight patients with hypertrophic cardiomyopathy were selected for study on the basis of technically suitable echocardiographic recordings. These 8 were selected from a total of 12 patients who fulfilled the following criteria of hypertrophic cardiomyopathy: I) clinical features that included sustained left ventricular apical impulse, rapid upstroke of the carotid pulse and systolic murmur along the left sternal border and apex that increased during the Valsalva maneuver (9-11); 2) M-mode echocardiographic features, including asymmetric septal hypertrophy with a septal to free wall ratio greater than 1.5 and systolic anterior motion of the anterior mitral leaflet (12-16); 3) two-dimensional echocardiographic features, including asymmetric distribution of hypertrophy, hypercontractile left ventricle and confirmation of systolic anterior motion on apical views (17); and 4) increased rest ejection fraction greater than 0.70 by radionuclide angiography using equilibrium blood pool scanning. Cardiac catheterization was carried out in only one patient because we no longer consider it a necessary test to confirm the diagnosis of hypertrophic cardiomyopathy in the presence of the mentioned clinical and noninvasive findings. In this patient, the diagnosis was supported by cardiac catheterization, which demonstrated a provocable left ventricular outflow pressure gradient of 50 mm Hg. All eight patients were men ranging in age from 55 to 67 (mean ± standard deviation 61.5 ± 3.8) years. 0735-1097/83/0401024-7$0300

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Eight normal men, all under the age of 35 (mean 3 / .0 ± 2.3) years , constituted the control group . These subjects had I ) no objective evidence of cardiovascular disease by clinical electrocardiographic and echocardiographic criteria. and 2) technically adequate two-dimensional echocardiographic studies for the purpose of an objective evaluation of left ventricular wall m oti on and thickening. Echocardiographic technique. All subjects were studied in a partial left lateral decubitus position. A commercially available (Varian 30(0) wide-angle, phased-array system was used With a 2.25 MHz transducer. Real-time images were recorded on a 0.5 inch (1.27 em) videotape cassette on a Sanyo video recorder capable of playback in real-time, slow motion and stop action modes. The standard parasternal long and short axis views were obtained. The apical four chamber view was obtained by placmg the transducer over the left ventricular apex ( 18). This view afforded a cross-sectional interrogation of the interventricular septum along its entire length from base to apex. permitting analysis of multiple levels of the septum during the same cardiac cycle. The acceptable technical quality required that the endocardial margins of the septum and left ventricular free wall be recorded without echo dropout. The separately obtained M-mode echocardiographic recordings of the patients with hypertrophic cardiomyopathy were also analyzed for septal thickening and septal and left ventricular free wall excursions. Analysis of data. Although a visual assessment of the interventricular septum and the free walls was made in all the cross sections described. the apical four chamber view was the purpose of quantitative analysis of the data (Fig. I .

Figure 1. Apical four chamber view from a patient with hypertrophic cardiomyopathy using two-dimensional echocardiography (left) . Thr s view was used for the quant itat ive analysis of septal thickening and septal and free wall motion End-diastolic (A) and end-systolic (8) frames of the same cardiac cycle are seen. Diagramm atic representation at right. AML = anterior mitral leaflet. lVS = interventricular septum. LA = left atrium: LV = left ventricle. PML = posterior mitral leaflet : PW = posteno r wall: RA '" right atrium: RV = fight ventricle. SAM = systolic anterior motion

for selection of this view included I ) adequate endocardial tracings at all levels of the interventricular septum from base to apex. 2) ability to make measurements at all levels of the septum and the lateral free wall in the same cardiac cycle. and 3) little Influence on the traced images of relatively small side to side cardiac motion in a plane perpendicular to the long axis of the left ventricle as compared with its motion in the anteroposterior plane. AnalYSIS was done using both fixed and floating systems of ref erence similar to those that have been described previously ( /9 .20). Our method differed from the onginal description in that instead of taking the center of the cavity as point of reference for both systems. we chose the central long axis of the entire left ventricular cavity as plane of reference. Our contention was that in the apical four chamber view. unlike the short axis view. free wall and septal motion can be better represented by referring to an axis rather than a point. End-diastolic and end-systolic fra mes were selected from the same cardiac cycle using the stop action mode. The endocardial edges of the entire left ventricular chamber and either side of the septum were traced in each frame on a clear plastic sheet. The hinge points of the mitral leaflet were identified and a horizontal line connecting them was drawn (Fig. 2). From the midpoint of this line and perpendicular to it. a vertical line (v) was drawn dividing the left ventricular chamber along its long axis. This line was then divid ed into four equal segments by lines (chord segments) drawn at right angles to it. Thus. each frame of the left ventricular cavity was divided into eight areas and the septum into

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( Figure 2. Diagrammatic representation of tracmg of left ventricular cavity and interventricular septum. The method used for the nomenclature of chords (I to 9) and areas (a to f) is shown. The lowest horizontal dashed line represents the line connecting the hinge points of the mitral leaflets. Fromthe midpoint of this line and perpendicularto It, the lme (v) IS drawn which divides the cavity into a lateral and a medial part. The numbers represent the chord segments and the letters represent areas. (See text for details.) The hatched areas are considered part of the apex and their analysis is not included in this report. LS = lower segment; MS = middle segment; US = upper segment.

Septal thickening was measured as percent change in chord segment and expressed as:

End-systolic thickness - End-diastolic thickness x 100. End-diastol ic thickness Thus, changes in chord segments I, 2 and 3 in Figure 2 represent septal thickening of lower, middle and upper segments of the interventricular septum. Septal and free wall motion was measured as percent change in both chord segments and areas. Areas were measured in order to analyze segmental j unction. Each area was measured with planimetry and percent change in area was expressed as: End-diastolic area - End-systolic area - - - - - ----<---End-diastolic area

Figure 3. Diagrammatic representation of the fixed reference system that simulates M-mode echocardiography where measurements for both enddiastolic (solid lines) and end-systolic (dashed lines) frames are made from the vertical line (v) and chord segments drawn for the end-diastolic frame . (See text for details.) Abbreviations as before. The fixed reference system was meant TO represent Msmode echocardiogra phy, In this system. the line drawn along the long axis of the left ventricle for end-diasto le formed the reference line from which all chord segments and areas were drawn. Septal thickness and septal and free wall motion were measured in reference to landmarks drawn only for the end-diastolic frame (Fig. 3) . In the floa ting reference system , the two-dimensional images for both end-diastole and end-systole were each assigned an independent reference system so that. unlike the fixed reference system. separate long axis and chord segments were drawn for the end-systolic frame. Measurements of chord segments and areas

Figure 4. Diagrammatic representation of the floating reference system where the vertical lme (v) and chord segments are independent for both end-diastolic (left) and end-systolic (right) frames (See text for deta sls.) Abbreviations as before.

x 100 .

Thus, changes in areas a and b represent lower septal and corresponding free wall motion and changes in areas c and d represent midseptal and corresponding free wall motion (Fig. 2). As a result of total cardiac motion , a part of the left atn um is included in areas e and f when the fixed reference system is used (Fig. 3). Change in area measured in these segme nts would incorporate both left ventricular wall and mitral anular systolic excursion using the fixed reference system. Hence, the upper septal and corresponding free wall motion is represented as percent change in chord segments only. In Figure 2, changes in chord segments 4, 5 and 6 reflect septal motion, and changes in chord segments 7, 8 and 9 represent free wall motion.

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were thus made fromafloating, ratherthan a fi xedreference system (Fig. 4). Statistical analysis of data util ized analysis of variance and the paired t test. Means of thetwo groups wereconsidered statistically significant at a probability (p) value of < 0.05.

Results Interventricular septal thickening. Normal subjects demonstrated the least percent thickening in the upper sep-

Figure 6. M-mode echocardi ogram from the patient whose two-dimensional frames are shown in Figure I. Note that the septal thickenmg and motion are evaluated at the level of the mitral leaflets and appear diminished (See text for details). ASH = asymmetric septal hypertrophy; EKG = electrocardiogram: FW = free wall; IVS = interventricular septum. LV = left ventricle: PP = posterior perica rdium. PW = posten or wa ll; RV = n ght ventricle ; SAM = systolic anterior motion; SM = systolic murmur

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tum and the most in the lower septum. The hypertrophied septum in patients with hypertrophic cardiomyopathy showed a similar variation with the least percent thickening in the upper third and the highest in the lower third (p < 0.05) (Fig. 5) . The percent thickening of the septum at all levels in patients with hypertrophic cardiomyopathy was not significantly different from that of the normal subjects when the floating reference system was used. When the fixed reference system was used, the upper part of the septum was noted to thicken significantly less than normal in the patients with hypertrophic cardiomyopathy (p < 0.05). This was not the case for the middle and lower segments of the septum. M-mode echocardiogramsperformed previously on these patients with hypertrophic cardiomyopathy showed that only the upper septum at the level of the mitral leaflets had been adequately sampled (Fig. 6). This part of the septum was noted to be relatively hypokinetic with a percent thickening of 8.3 ± 4.4% . Interventricular septal motion. With the fixed reference system, the upper septum (chord 6 in Fig. 3) moved significantly less in patients with hypertrophic cardiomyopathy than in normal subjects (p < 0.05) (Fig. 7). There was no difference in motion of middle and lower segments of the septum between normal subjects and patients with hypertrophic cardiomyopathy with this system (Fig. 8) . With the floating reference system, there was no difference in upper and lower septal motion between normal subjects and patients with hypertrophic cardiomyopathy (Fig. 7 and 8); however, the middle septum moved more in these patients than in the control group (p < 0.05) (Fig. 8). Analysis of M-mode echocardiograms at the level of the mitral valve in patients with hypertrophic cardiomyopathy showed septal systolic motion of 9.2 ± 2.2% as compared with the free wall motion of 40.5 ± 4.4 %. The echocardiograms at the level of the chordae tendineae were technically unsatisfactory for accurate measurements.

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Free wall motion. With the fixed reference system, the upper septum mo ved significantly less than the corre sponding free wall in patients with hypertroph ic cardiomyopathy (p < 0 .05); this was not the case in normal subjects. With the floatin g reference sys tem, there was no significant difference in the upper septal and corres ponding free wall motion (Fig. 7). With the fixed reference sys tem , the rmddle septum and corre spo nding free wall moved eq ually well in both gro ups while with the floatin g refere nce sys tem , the middle septum moved more than the correspond ing free wall in pati ent s with hypertrophic cardiomyopathy (p < 0. 05) (Fig . 8) . With either system , the lower septum mo ved more than the correspond ing free wall in both gro ups (p < 0.05), and the lower free wall motion was simil ar in both groups.

Discussion Comparison of two-dimensional and M-mode echocardiographic results. Our res ults utilizing two-d imensio nal ech ocardiography dem onstrate that the interventricular septum in hypertrophic cardio myo pathy , far from being akinetic, shows normal thickenin g and normal or incre ased exc ursion. Th is is especially true of the middle and lower third s of the septum . Even in normal subjects, the upper

Figure 7. Upper septal and corresponding free wall motion as evaluated by both fixed (A ) and floating (B) reference systems Abbreviations as before A) FIXED REFERENCE SYSTEM

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third of the septum move s less than the middle and lower thirds. This probably res ults from its anato mic co ntig uity with the aorta . Thi s port ion of the septum thu s acts as a hinge point between the posteriorly moving middle and lower thirds of the septum and the anterio rly moving aort a (2 1). We contend that techni cally adequate M-m ode echoc ardiograms are frequently not obtainable below the level of the mitral valve in patients with hypertrophic cardi omyop athy, probabl y because of the geo metric distorti on and small size of the left ventricle in these patient s. A careful review of the illustrations in most of the ea rlie r report s (1 ,2,4) descri bing the interventricular septum as hypokinetic or akinetic lends support to our claim . A second cause of the discrepancy between our findings and those of earlier reports using M-m ode echocardiography may be related to the system of reference used . The Mmode technique repre sents a fixed sys tem of reference in that the M-m ode tran sduc er remains fixed, and the moving struct ures are recorded in reference to the relati vely fixed chest wall. Thu s, as a result of cardiac mot ion , different parts of the interventricular septum may be sampled during diastole and systole. In addition. the posterior excursio n of the left ventricular endocardi um of the interventri cul ar septum may appear decreased beca use of the overall anterior motion of the heart in systole. To highli ght this point , we chose the fixed reference syste m , which simulates M-m ode echoca rdiography . Th e result s of upper septal motion and thickening using this method of refere nce are similar to those obtained using M-mode ec hocardiog raphy. The dynamic nature of the interventricular septum in hypertrophic cardiomyopathy is readily visualized in the real-time playback of two-d imensional echocardiograph ic recordin gs of images obt ained in the para sternal long and short axis as well as apic al fou r chamber views. For the purposes of analysis, we chose the apica l view, as in this view the entire length of the septum is visualized simultaneou sly and its thickening and mot ion can be mea sured in the same cardiac cycle . Th e endocardial definition s in this view were free of ec ho dropout and could be adequately outlined by hand in all the subjec ts included in the study . Potential limitations of study. Th ere are some potential limitation s to our approach. First , the four chamber view of the septum and free walls affords a less precise lateral resoluti on of the se struc tures . Thu s, it is likel y that the thickn ess measurement at vario us levels may have been over- estimated . Qu antitation of change in thickne ss and endocardial exc urs ion, ho wever, should not be influenced significantl y . Moreover , any shortco mings inherent in this particular cro ss sec tion should apply equally to both gro ups of subjec ts being studied . Because both the anter ior and posterior portions of the interventricular septum are see n in the para sternal short axis view and as poor lateral resoluti on may contribute less to errors in this view, the short axis view would appear more

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Figure 8. Motion, of the middle and lower parts of the septumand their corresponding free walls as measured by both the fixed (A) and floatmg (8) reference systems. Abbreviations as before.

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suitable for the study of left ventricular segmental wall motion . However , our efforts to outline the endocardial surface of the left ventricle at the level of the papillar y muscles in patients with hypertrophic cardiomyopathy were not uniform ly successful, owin g to the extremely small and overcrowded left ventricular cavity during systole . The second potential limitation of our technique is that it fails to asses s the effects of cardiac rotation during systole. However, visualization of both atrioventricular valves throughout the cardiac cycle assures that our measurements were made at the level of the interventri cul ar septum and that the effec ts of rotation are probably small. Comparison with previous reports. Ear lier cineangio grap hic studies (22) utilizing left anterior oblique views which are somewhat comparable with the two-dimensional apical four chamber view , have described the interventricular septum to move well dur ing systole. A more recent study (23) using biventricul ar cinea ngiography report ed increase d bulgin g of the left ventric ular septal surface durin g systole. In add ition , a significant (p < 0 .0 I ) increase in the mean septal thickness of approxi mately 20% (from 15.2 ::!:: 1.5 mm [mean ± standard deviation ) in diastole to 18.3 ± 1.8 mm in end-systole) at the leve l of the j unction of upper and middle thirds of the septum was noted . A study (24) utilizi ng two-dim ensional echoca rdiography to assess catenoid shape of the interve ntricular septum in hypertrophic cardiomyopathy was publi shed recently . An ancillary conclusion reached was that the septum is akinetic. The septum in that study was measured at the points of

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maximal curvature in two different views, and the sum of the thicknesses in the two views was compared in diastole and systole . Th is analysis assumed that the point of maximal curva ture was the same in both views and each frame. The entire length of the septum was not analyzed for thicken ing and motion . We believe that that study is not conclusive in regard to the observations on septal dynamics. Conclusions. Our study has shown that there is no difference in the thickening of the middl e and lower segments of the interventricular septum between normal subjects and patients with hypertrophic cardiom yopathy. The upper septum appears to thicken less in patients with hypert roph ic cardio myo pathy only when the fixed refere nce system is used . Our eva luation of regional wall motion has also demonstrated that the upper and lower seg ments of the septum move equally well in patients with hypert roph ic cardiomyopathy and in norm al subjec ts; while the middle septum, using the floating reference system , moves more in those with hypert rophic cardiomyopathy. In addition, our study shows that the lower septum is more dynam ic than the correspo nding free wall. The upper septum see ms to move less than the corresponding free wa ll only when the fixed reference system is used . Our results fail to support the wide ly held notion that the interven tricular septum in hypertrophic cardio myo pathy is akinetic. Earlier reports described the septum as akinetic utilized M-mode echocardiography. In these reports, the system was generally anal yzed at the mitral valve level. The upper septum moves and thickens less even in normal per-

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sons. Moreover, the fixed reference mode of M-mode echocardiography may have influenced the measurements of septal excursion and thickening as noted in our study. By using the floating reference system with two-dimensional echocardiographic images, we observed normal moving and thickening of the interventricular septum at all levels.

10. Shah PM. Newer concepts In hypertrophic obstructive cardiomyopathy. II. lAMA 1979;242'1771-6 II. Frank S, Braunwald E Idiopathic hypertrophic subaortic stenosisclinical analysis of 126 patients with emphasis on the natural history.

Circulation 1968;37:759-88. 12. Shah PM, Gramiak R, Kramer DH. Ultrasound localization of left ventricular outflow obstruction in hypertrophic obstructive cardiomyopathy. Circulation 1969;40:3-11.

13. Shah PM, Gramiak R, Adelman AG Role of echocardiography We gratefully acknowledge the help of Kaye Cherry for her expert secretarial assistance in preparation of the manuscript, Linda Leib for making the illustrations and Bramah N. Singh, MD, for his critical review.

In

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14 Shah PM Echocardiography

In the dragnosis of hypertrophic obstructive cardiomyopathy. Am 1 Med 1977;62:830-5.

15. Abbasi A, MacAlpin RN, Eber LM, et al. Left ventricular hypertrophy diagnosed by echocardrography. N Engl J Med 1973:289.118-21. 16. Henry WL, Clark CE, Epstein SE. Asymmetrical septal hypertrophy:

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