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Echocardiography and Pathology of Left Ventricular “False Tendons”
Echocardiography and Pathology of Left Ventricular "False Tendons"* Abdel K. Abdulla, M.D.; *Andrea Frustaci, M.D., F.C.C.P.; Jhorque E. Martinez, M.D .; Richard A. Florio, F.l.M.C.S.; Jane Somerville, M.D., F.R .C.P.; and Eckhardt G. J Olsen, M.D., F.R.C.lbth.
The anatomic incidence ofleft ventricular false tendons has been determined in 100 hearts obtained from consecutive autopsies on patients who had a wide variety of cardiac conditions. In this series, an anomalous band was found in 34 cases. A retrospective ~mensional (2D) echocardiographic study was able to identify false tendons in only 18 percent of cases with anatomic evidence of them, indicating
2 mm as the limit of resolution of 2D echocardiography even with appropriate projections. Finally, the histologic examination has shown false tendons to contain conduction tissue and thus it is assumed to be intracavitary radiations of the bundle of His. This last consideration introduces new physical and electrophysiologic implications. (Cheat 1990; 98:129-32)
The presence of an "anomalous band" or "false tendon" has been noted in some patients undergoing echocardiography for different cardiac conditions.1-6 This band originates in the interventricular septum, stretches across the left ventricular cavity, and usually inserts into one of the papillary muscles. It may be found in association with cardiac abnormalities or as an isolated finding. 4 •5 It is usually of no clinical significance, but it has been associated with rate-dependent ventricular arrhythmias3 and described as giving rise to a musical murmur when pulled taut by ventricular dilatation. 7 This anomalous band can be seen on two-dimensional (20) echocardiography and it is easily identified as a linear echo running from the free wall of the left ventricle or from the papillary muscle of the mitral valve to the interventricular septum in the long and short axis, parasternal, or apical four- or two-chamber view. 2 The reported incidence following a 20 echocardiogram varies between 0.5 and 61 percent.24 This great variability depends on many elements, including patient selection (adults vs children), method of approach (prospective vs retrospective), and the intrinsic thickening of false tendons. The purpose of this study is to assess the sensitivity of 20 echocardiograms on false tendons, comparing anatomic examination of 100 postmortem cases with the retrospective analysis of their echos. Furthermore, in our study, histologic study will be
undertaken to establish the exact nature of this anomalous band.
*From the National Heart and Chest Hospitals, London, EnJdand (Drs. Abdulla, Martinez, Florio, Somerville, and Olsen); anCJ the Cardiology Department, Catholic University School of Medicine, Rome, Italy (Dr. Frustaci). Manuscript received August 1, 1989; revision accepted January 23, 1990. Reprint requests: Dr. Frustaci , Cardiology, Largo A Gemelli 8, Rome, Italy 00168
MATERIALS AND METHODS
A series of 100 hearts taken from <.'Onsecutive postmortem cases on 34 female and 66 male patients of ages ranging from 2 months to 77 years were examined. The underlying cardiac (.'()nditions are set out in Thble l. In those cases where an anomalous band was found, blocks were selected from the septal area to include a longitudinal section of the hand and further blocks were selected from the papillary muscle. Transverse sections were also cut from the central portion of the band. All blocks were pro<.-essed for the routine paraffin wax embedding and hematoxylin-eosin and Millers elastic van Gieson stains. During life the patients had all undergone echocardiography (performed on an ATL-MK 600 and a Hewlett Packard 77020A) using 3.5- and 5-MHz transducers from the standard long and short parasternal axis and from apical four- and two-chamber views. The echocardiographs from those patients in whom an anomalous band was found macroscopically were reviewed to see if the band could be identified by this technique.
REsuLTS Of the 100 hearts examined from consecutive autopsies, 34 were found to have an anomalous band (18 female and 16 male). The band ran from septum (often close to the pars membranacea septi) to papillary muscle in 27 cases (Fig 1), and from septum to free Table !-Showing the Underlying Cardiac Condition" Heart Disease
No. of Cases
Ischemic Congenital Valvular Cardiomyopathy (dilated) Fihroelastoses Primary pulmonary hypertension Dissecting aortic aneurysm Atrial myxoma Ccmstrictive pericarditis
15 7
5 2
CHEST I 98 I 1 I JULY. 1990
129
many cases. Its length also varied greatly, measuring from 46 mm for those cases that transversed the cavity to 20 mm in those cases that reentered the septum . Microscopic examination showed these anomalous bands to be composed of a mildly thickened endocardimn of up to 3-J.Lm thickness (E, Fig 2) with underlying myocardial tissue that has all the features attributable to myogenic conducting tissue identical to that seen in the bundle of HisH (Fig 3). Indeed, the myocardial fibers present in the anomalous bands were smaller and thinner compared with working cardiocytes and were loosely arranged in a fascicle configuration (Fig 3, lower). In addition, each case showed a centrally placed thick-walled arteriole (A, Fig 2). A retrospective study of the echocardiograms of 32 of 34 cases found to have anomalous bands (the two remaining were technically unsuitable) resulted in only six being identified by this method. All of these were from cases that had a band of more than a 2-mm diameter. DISCUSSION
The literature dealing with "anomalous bands" had identified a frequency ofbetween 0 .5 and 61 percent2 •4
Ft<:t•IIE I. Vit"W of tht" le ft vt"ntride of a heart dearly showin~ tht" "anomalous hand " issuing from the interventricular septum and stretchin~ at·ross the cavity and inst"rtin~ into th .. left vt"ntricular frt"e wall (arrows).
wall in five cases. In the remaining two cases the band issued from and then reentet·ed the septum. The thickness of the hand was variable, ranging from a maximum of 3 mm diameter to less than 1 mm in
FtGlTIIE 2. Micro~raph of a cross section of hand tissue showin~ the thickened t"ndocardium (E). a thick-walled central artery (A), and hundles of myocardium and <.~mduction tissue (arrows) (hematuxylin-t"osin. x 250).
130
Ft<:tTIIE 3. Micrograph showing structural analogies between bundle of His (uppt'l') and an anomalous band (lvwer). Thin, small , loosely arranged myocardial fibres are ret~>gn ized in hoth structures (hematoxylin-eosin, X 250).
Echocardiography and Pathology of Left Ventricular "False Tendons" (Abdulla et a/)
with echocardiography. This wide variability depends on many elements, including patient selection (adults vs children), method of approach (prospective vs retrospective), and the intrinsic thiCkening of the bands. In particular, in studies of children, 1.4 the use of high-frequency transducers provides a superior resolution; in prospective studies, the sonographer is specifically oriented to look for the bands; and finally, very thin chordae are unlikely to be identified with echocardiography. As far as the last point is concerned, to our knowledge, there are no reports that compare the anatomy of false tendons with the resolution's rate of echocardiography. Furthermore, an extensive microscopic study of these chordae has not been previously undertaken. Our study analyzed 100 postmortem cases looking for left ventricular false tendons. The latter were identified in 34 percent of hearts, but by using conventional methods of echocardiography, only 18 percent of cases could be identified retrospectively from the group of patients shown to have an anomalous band. Short axis cut echocardiography and M-mode echocardiography did not demonstrate the band in any of the cases. The four-chamber approach with long axis, upwards-downwards tilting of the ultrasonic beam, was more successful because of the wider area of the ventricular cavity covered and as these structures run longitudinally rather than transversely across the cavity. Using this approach permitted visualization of the bands. A long, careful sweep across the whole ventricular length is necessary to ensure the location of this structure. The short axis view would tend to cut the band transversely, which in many cases would be of too small a diameter to be seen. The thickness of chordae is, on the other hand, the other crucial point in determining the sensitivity of echocardiography. In our study with this procedure only chordae with a diameter of more than 2 mm could be identified. Although 20 echocardiography is not ideal for the identification of these structures, angiography would appear to be ofless value with only one group documenting recognition by this technique.9 From a histologic point of view, anomalous bands have been reported as fibromuscular or muscular bands of little or no clinical significance. 3 •7 · 10 Our study has shown that these bands, often originating close to the pars membranacea septi (Fig 1) (where the bundle of His comes up), contain myocardial fibers that are smaller and thinner compared with working cardiocytes; they are loosely arranged in a fascicle configuration (Fig 3, lower), are covered by endocardium (E, Fig 2), and are supplied by a centrally placed, thick-walled arteriole (A, Fig 2). These fea-
tures are attributable to myogenic conducting tissue identical to that seen in the bundle of His8 and suggest left ventricular false tendons to be intracavitary radiations of the bundle of His. Figure 3 shows the structural analogies between the bundle of His (Fig 3, upper) and the anomalous band (Fig 3, lower). In particular, thin, small, loosely arranged myocardial fibers are identified in both structures. This contribution may increase the clinical significance of anomalous bands. In particular if as a result of dilatation this band should be ruptured, or as the result of surgery or ischemia a rupture should occur, abnormalities on contractility of the portion of the heart distal to the band could be apparent. Furthermore, the electrophysiologic implications may be more important than previously reported. In fact, in addition to the mechanical stretching causing musical murmur7 or rate-dependent ventricular premature beats,3 false tendons may give rise to a reentry mechanism being responsible for more severe arrhythmias like ventricular tachycardia and fibrillation. Indeed, it has been shown in a canine model that false tendons are a source of Purkinje fibers 11 • 12 and appear to have a gating mechanism that may either protect against or permit reentry from ventricular fibrillation. 13 It has also been shown experimentally that stretching of the band does cause electrophysiologic alterations. 14 Finally, interconnecting Purkinje fibers and ventricular muscle have been implicated in ventricular arrhythmias in human adults. 15 In conclusion, our study reveals left ventricular false tendons to be more numerous than those detectable with 20 echocardiograms, which has a limit of resolution of 2 mm; the bands are found to contain conduction tissue and assumed to be intracavitary radiations of the bundle of His; therefiJre, their clinical significance may be more relevant than previously believed and should be prospectively reconsidered. REFERENCES 1 Okamoto M, Nal(ata S, Park YD . et ul. Visuali7.ation of the false tendon in the lefi ventricle with cchocardio!(raphy and its clinical significam:e. J Cardiol1981 ; 11:265-70 2 Nishimura T, Kondo M, Umadome H. Shomono Y. Echo<.·ardio!(raphic features of false tendons in the lefi ventricle. Am J Cardioll981 ; 48:177-83 3 Perry L\V, Ruckman RN, Shapiro SR. Knell KS , Galioto FM, S1.~>tt LP. Left ventricular false tendons in children: prevelance as detected by 2-dtmensionul echocurdto!(raphy and clinical significance. Am J Curdioll983; 52:1264-66 4 Brenner Jl , Baker FK, Rin~otcl RE, Berman MA . Echocardiographic eviden1.-e ofleft ventricular hands in infants and children. JAm Coli Cardioll984; 3:1515-20 5 Turner W A human heart with rn
131
7
8 9 10 11
as determined by echocardiography. Am J Cardiol1984; 53:33032 Roberts we. Anomalous left ventricular band: an unemphasized cause of a precordial musical munnur. Am J Cardiol 1969; 23: 735-38 Davies MJ, Anderson RH, Baker AE. The conduction system of the heart. London, England: Butterworths; 1983:9-70 Goebel VN , Schneider J. Falsche Sehnenfaden in Lavogramm. ROFO 1978; 128:371-72 McKusick VA. Cardiovascular sound in health and disease. Baltimore, Md: William & Wilkins; 1958: 209-11 Anniger LC, Urthaler F, James TN. Morphological changes in the right ventricular septomarginal trabecula (false tendons) during maturation aging in the dog heart. J Anat 1979; 129:80517
12 Katholi RE, Woods WT, Kawamur.1 K, Urthaler F, James TN . Dual dependence on both Ca • • and Mg • • for electrical stability in cells of canine tendon. J Mol Cell Cardiol1979; 11:435-45 13 Myerberg RJ, Gelband H, Hoffman BF. Functional characteristics of the gating mechanism of the canine A-V conduction system . Circ Res 1971; 28:136-47 14 Sanders R, Myeberg RJ, Gelband H , Bassett AL. Dissimilar length-tension relations of canine ventricular muscle and false tendon: electrophysiologic alterations accompanying deformation. J Mol Cell Cardiol1979; 11:209-19 15 Wit AL, Rosen MR. Cellular electrophysiology of cardiac arrhythmias, II: arrhythmias caused by abnormal impulse (.'()nduction. Mod Cone Cardiovasc Dis 1981; 50:7-12
Plan to Attend ACCP's
56th Annual Scientific Assembly Toronto, Ontario, Canada
October 22-26, 1990
132
Echocardiography and Palhology of Left ventricular "False Tendons'" (Abdulla et al)
The anatomic incidence ofleft ventricular false tendons has been determined in 100 hearts obtained from consecutive autopsies on patients who had a wide variety of cardiac conditions. In this series, an anomalous band was found in 34 cases. A retrospective ~mensional (2D) echocardiographic study was able to identify false tendons in only 18 percent of cases with anatomic evidence of them, indicating
2 mm as the limit of resolution of 2D echocardiography even with appropriate projections. Finally, the histologic examination has shown false tendons to contain conduction tissue and thus it is assumed to be intracavitary radiations of the bundle of His. This last consideration introduces new physical and electrophysiologic implications. (Cheat 1990; 98:129-32)
The presence of an "anomalous band" or "false tendon" has been noted in some patients undergoing echocardiography for different cardiac conditions.1-6 This band originates in the interventricular septum, stretches across the left ventricular cavity, and usually inserts into one of the papillary muscles. It may be found in association with cardiac abnormalities or as an isolated finding. 4 •5 It is usually of no clinical significance, but it has been associated with rate-dependent ventricular arrhythmias3 and described as giving rise to a musical murmur when pulled taut by ventricular dilatation. 7 This anomalous band can be seen on two-dimensional (20) echocardiography and it is easily identified as a linear echo running from the free wall of the left ventricle or from the papillary muscle of the mitral valve to the interventricular septum in the long and short axis, parasternal, or apical four- or two-chamber view. 2 The reported incidence following a 20 echocardiogram varies between 0.5 and 61 percent.24 This great variability depends on many elements, including patient selection (adults vs children), method of approach (prospective vs retrospective), and the intrinsic thickening of false tendons. The purpose of this study is to assess the sensitivity of 20 echocardiograms on false tendons, comparing anatomic examination of 100 postmortem cases with the retrospective analysis of their echos. Furthermore, in our study, histologic study will be
undertaken to establish the exact nature of this anomalous band.
*From the National Heart and Chest Hospitals, London, EnJdand (Drs. Abdulla, Martinez, Florio, Somerville, and Olsen); anCJ the Cardiology Department, Catholic University School of Medicine, Rome, Italy (Dr. Frustaci). Manuscript received August 1, 1989; revision accepted January 23, 1990. Reprint requests: Dr. Frustaci , Cardiology, Largo A Gemelli 8, Rome, Italy 00168
MATERIALS AND METHODS
A series of 100 hearts taken from <.'Onsecutive postmortem cases on 34 female and 66 male patients of ages ranging from 2 months to 77 years were examined. The underlying cardiac (.'()nditions are set out in Thble l. In those cases where an anomalous band was found, blocks were selected from the septal area to include a longitudinal section of the hand and further blocks were selected from the papillary muscle. Transverse sections were also cut from the central portion of the band. All blocks were pro<.-essed for the routine paraffin wax embedding and hematoxylin-eosin and Millers elastic van Gieson stains. During life the patients had all undergone echocardiography (performed on an ATL-MK 600 and a Hewlett Packard 77020A) using 3.5- and 5-MHz transducers from the standard long and short parasternal axis and from apical four- and two-chamber views. The echocardiographs from those patients in whom an anomalous band was found macroscopically were reviewed to see if the band could be identified by this technique.
REsuLTS Of the 100 hearts examined from consecutive autopsies, 34 were found to have an anomalous band (18 female and 16 male). The band ran from septum (often close to the pars membranacea septi) to papillary muscle in 27 cases (Fig 1), and from septum to free Table !-Showing the Underlying Cardiac Condition" Heart Disease
No. of Cases
Ischemic Congenital Valvular Cardiomyopathy (dilated) Fihroelastoses Primary pulmonary hypertension Dissecting aortic aneurysm Atrial myxoma Ccmstrictive pericarditis
15 7
5 2
CHEST I 98 I 1 I JULY. 1990
129
many cases. Its length also varied greatly, measuring from 46 mm for those cases that transversed the cavity to 20 mm in those cases that reentered the septum . Microscopic examination showed these anomalous bands to be composed of a mildly thickened endocardimn of up to 3-J.Lm thickness (E, Fig 2) with underlying myocardial tissue that has all the features attributable to myogenic conducting tissue identical to that seen in the bundle of HisH (Fig 3). Indeed, the myocardial fibers present in the anomalous bands were smaller and thinner compared with working cardiocytes and were loosely arranged in a fascicle configuration (Fig 3, lower). In addition, each case showed a centrally placed thick-walled arteriole (A, Fig 2). A retrospective study of the echocardiograms of 32 of 34 cases found to have anomalous bands (the two remaining were technically unsuitable) resulted in only six being identified by this method. All of these were from cases that had a band of more than a 2-mm diameter. DISCUSSION
The literature dealing with "anomalous bands" had identified a frequency ofbetween 0 .5 and 61 percent2 •4
Ft<:t•IIE I. Vit"W of tht" le ft vt"ntride of a heart dearly showin~ tht" "anomalous hand " issuing from the interventricular septum and stretchin~ at·ross the cavity and inst"rtin~ into th .. left vt"ntricular frt"e wall (arrows).
wall in five cases. In the remaining two cases the band issued from and then reentet·ed the septum. The thickness of the hand was variable, ranging from a maximum of 3 mm diameter to less than 1 mm in
FtGlTIIE 2. Micro~raph of a cross section of hand tissue showin~ the thickened t"ndocardium (E). a thick-walled central artery (A), and hundles of myocardium and <.~mduction tissue (arrows) (hematuxylin-t"osin. x 250).
130
Ft<:tTIIE 3. Micrograph showing structural analogies between bundle of His (uppt'l') and an anomalous band (lvwer). Thin, small , loosely arranged myocardial fibres are ret~>gn ized in hoth structures (hematoxylin-eosin, X 250).
Echocardiography and Pathology of Left Ventricular "False Tendons" (Abdulla et a/)
with echocardiography. This wide variability depends on many elements, including patient selection (adults vs children), method of approach (prospective vs retrospective), and the intrinsic thiCkening of the bands. In particular, in studies of children, 1.4 the use of high-frequency transducers provides a superior resolution; in prospective studies, the sonographer is specifically oriented to look for the bands; and finally, very thin chordae are unlikely to be identified with echocardiography. As far as the last point is concerned, to our knowledge, there are no reports that compare the anatomy of false tendons with the resolution's rate of echocardiography. Furthermore, an extensive microscopic study of these chordae has not been previously undertaken. Our study analyzed 100 postmortem cases looking for left ventricular false tendons. The latter were identified in 34 percent of hearts, but by using conventional methods of echocardiography, only 18 percent of cases could be identified retrospectively from the group of patients shown to have an anomalous band. Short axis cut echocardiography and M-mode echocardiography did not demonstrate the band in any of the cases. The four-chamber approach with long axis, upwards-downwards tilting of the ultrasonic beam, was more successful because of the wider area of the ventricular cavity covered and as these structures run longitudinally rather than transversely across the cavity. Using this approach permitted visualization of the bands. A long, careful sweep across the whole ventricular length is necessary to ensure the location of this structure. The short axis view would tend to cut the band transversely, which in many cases would be of too small a diameter to be seen. The thickness of chordae is, on the other hand, the other crucial point in determining the sensitivity of echocardiography. In our study with this procedure only chordae with a diameter of more than 2 mm could be identified. Although 20 echocardiography is not ideal for the identification of these structures, angiography would appear to be ofless value with only one group documenting recognition by this technique.9 From a histologic point of view, anomalous bands have been reported as fibromuscular or muscular bands of little or no clinical significance. 3 •7 · 10 Our study has shown that these bands, often originating close to the pars membranacea septi (Fig 1) (where the bundle of His comes up), contain myocardial fibers that are smaller and thinner compared with working cardiocytes; they are loosely arranged in a fascicle configuration (Fig 3, lower), are covered by endocardium (E, Fig 2), and are supplied by a centrally placed, thick-walled arteriole (A, Fig 2). These fea-
tures are attributable to myogenic conducting tissue identical to that seen in the bundle of His8 and suggest left ventricular false tendons to be intracavitary radiations of the bundle of His. Figure 3 shows the structural analogies between the bundle of His (Fig 3, upper) and the anomalous band (Fig 3, lower). In particular, thin, small, loosely arranged myocardial fibers are identified in both structures. This contribution may increase the clinical significance of anomalous bands. In particular if as a result of dilatation this band should be ruptured, or as the result of surgery or ischemia a rupture should occur, abnormalities on contractility of the portion of the heart distal to the band could be apparent. Furthermore, the electrophysiologic implications may be more important than previously reported. In fact, in addition to the mechanical stretching causing musical murmur7 or rate-dependent ventricular premature beats,3 false tendons may give rise to a reentry mechanism being responsible for more severe arrhythmias like ventricular tachycardia and fibrillation. Indeed, it has been shown in a canine model that false tendons are a source of Purkinje fibers 11 • 12 and appear to have a gating mechanism that may either protect against or permit reentry from ventricular fibrillation. 13 It has also been shown experimentally that stretching of the band does cause electrophysiologic alterations. 14 Finally, interconnecting Purkinje fibers and ventricular muscle have been implicated in ventricular arrhythmias in human adults. 15 In conclusion, our study reveals left ventricular false tendons to be more numerous than those detectable with 20 echocardiograms, which has a limit of resolution of 2 mm; the bands are found to contain conduction tissue and assumed to be intracavitary radiations of the bundle of His; therefiJre, their clinical significance may be more relevant than previously believed and should be prospectively reconsidered. REFERENCES 1 Okamoto M, Nal(ata S, Park YD . et ul. Visuali7.ation of the false tendon in the lefi ventricle with cchocardio!(raphy and its clinical significam:e. J Cardiol1981 ; 11:265-70 2 Nishimura T, Kondo M, Umadome H. Shomono Y. Echo<.·ardio!(raphic features of false tendons in the lefi ventricle. Am J Cardioll981 ; 48:177-83 3 Perry L\V, Ruckman RN, Shapiro SR. Knell KS , Galioto FM, S1.~>tt LP. Left ventricular false tendons in children: prevelance as detected by 2-dtmensionul echocurdto!(raphy and clinical significance. Am J Curdioll983; 52:1264-66 4 Brenner Jl , Baker FK, Rin~otcl RE, Berman MA . Echocardiographic eviden1.-e ofleft ventricular hands in infants and children. JAm Coli Cardioll984; 3:1515-20 5 Turner W A human heart with rn
131
7
8 9 10 11
as determined by echocardiography. Am J Cardiol1984; 53:33032 Roberts we. Anomalous left ventricular band: an unemphasized cause of a precordial musical munnur. Am J Cardiol 1969; 23: 735-38 Davies MJ, Anderson RH, Baker AE. The conduction system of the heart. London, England: Butterworths; 1983:9-70 Goebel VN , Schneider J. Falsche Sehnenfaden in Lavogramm. ROFO 1978; 128:371-72 McKusick VA. Cardiovascular sound in health and disease. Baltimore, Md: William & Wilkins; 1958: 209-11 Anniger LC, Urthaler F, James TN. Morphological changes in the right ventricular septomarginal trabecula (false tendons) during maturation aging in the dog heart. J Anat 1979; 129:80517
12 Katholi RE, Woods WT, Kawamur.1 K, Urthaler F, James TN . Dual dependence on both Ca • • and Mg • • for electrical stability in cells of canine tendon. J Mol Cell Cardiol1979; 11:435-45 13 Myerberg RJ, Gelband H, Hoffman BF. Functional characteristics of the gating mechanism of the canine A-V conduction system . Circ Res 1971; 28:136-47 14 Sanders R, Myeberg RJ, Gelband H , Bassett AL. Dissimilar length-tension relations of canine ventricular muscle and false tendon: electrophysiologic alterations accompanying deformation. J Mol Cell Cardiol1979; 11:209-19 15 Wit AL, Rosen MR. Cellular electrophysiology of cardiac arrhythmias, II: arrhythmias caused by abnormal impulse (.'()nduction. Mod Cone Cardiovasc Dis 1981; 50:7-12
Plan to Attend ACCP's
56th Annual Scientific Assembly Toronto, Ontario, Canada
October 22-26, 1990
132
Echocardiography and Palhology of Left ventricular "False Tendons'" (Abdulla et al)