Familial cardiac myxoma

Familial cardiac myxoma Emphasis on unusual clinical manifestations This report describes familial cardiac myxoma involving parent and child. The familial occurrence of this condition, previously reported in four other families, underscores the necessity of screening all direct members of the family by echocardiography once the diagnosis of cardiac myxoma is made. Each patient presented with unusual clinical manifestations. The father, who had a right atrial myxoma associated with an atrial septal defect and mitral valve prolapse, presented with findings highly suggestive of paradoxical embolism. The daughter, who had an infected right ventricular myxoma, was initially treated for valvular subacute bacterial endocarditis before the diagnosis was made.

James C. Powers, M.D., Michael Falkoff, M.D., Robert A. Heinle, M.D., Navin C. Nanda, M.D., Ling S. Ong, M.D., Robert S. Weiner, M.D., and S. Serge Barold, M.B., F.R.A.C.P., Rochester, N. Y.

Although rare, cardiac myxomas recently have generated a great deal of interest because they represent a potentially curable form of serious heart disease which can be diagnosed easily and accurately by echocardiography. Several recent reports also have emphasized a familial occurrence, t-5 so that it is almost imperative to screen all immediate members of the family once the diagnosis of cardiac myxoma is made. We describe in this report the familial occurrence of right-sided cardiac myxoma in a father and daughter. Each had unusual clinical manifestations.

Case reports CAS E 1. The first patient is a 19-year-old woman whose echocardiograms formed the subject of a previous publication." She was admitted to the Genesee Hospital on Oct. 23, 1975, for the evaluation of weakness, headache, general malaise, and intermittent fever with shaking chills and night sweats for about I week. There was no past history of rheumatic fever, but examination I year before admission had revealed a systolic murmur. Minor dental work had been performed without antibiotic prophylaxis 3 months before

From the Division of Cardiology, Department of Medicine, The Genesee (Louis and Molly Wolk Ultrasound Laboratory) and Strong Memorial Hospitals, University of Rochester School of Medicineand Dentistry, and the Department of Surgery, Rochester General Hospital, Rochester, N. Y. Received for publication Oct. 12, 1978. Accepted for publication Nov. 21, 1978. Addressfor reprints: Dr. S. Serge Barold,The Genesee Hospital, 224 Alexander St., Rochester, N. Y. 14607.

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admission. On examination the temperature was 38° C.; the pulse rate was 96 beats per minute and regular, and the blood pressure was 110/70 mm. Hg. There was a systolic thrill in the second left intercostal space but no abnormal precordial impulses. On auscultation there was a pulmonary ejection click (louder with expiration) followed by a Grade 3/6 ejection systolic murmur, best heard in the second left intercostal space, and a Grade 1/6 low-pitched early diastolic murmur along the left sternal edge. No other diastolic sounds were audible. Findings from the rest of the physical examination were unremarkable. The chest roentgenogram showed no abnormalities and the electrocardiogram showed normal sinus rhythm, right axis deviation, and a tall R wave in Lead Vb compatible with right ventricular hypertrophy. Laboratory data. Laboratory values were as follows: Hematocrit 34 percent, white blood count 11,400 per cubic millimeter with 86 percent segmented forms and II percent lymphocytes, platelet count within nonnallimits, sedimentation rate (Westergren) 60 mm. in I hour, and total protein 7.4 Gm. per 100 ml. with the gamma globulin fraction constituting 21 percent. Urinalysis, blood urea nitrogen (BUN), creatinine, T3 and T4 (radio immunoassay), electrolytes, glucose, serum iron, and total iron binding capacity all were within normal limits. The reticulocyte count was 5.4 percent, the haptoglobin value was decreased to 18 mg. per 100 ml. (normal 60 to 270 mg. per 100 ml.), and the serum bilirubin value was 0.6 mg. per 100 ml. Urinary urobilogen was within normal limits. The lactic dehydrogenase (LDH) value was 246 (normal 30 to 90) with the LDH-I fraction greater than the LDH-2 fraction. The lupus erythematosis preparation and antinuclear and rheumatoid factors were negative, but the C reactive protein was strongly positive. The patient remained febrile for I week with spiking temperatures to 39.5° C. Nineteen of 22 blood cultures grew an alpha hemolytic streptococcus highly sensitive to penicillin, and the clinical diagnosis was bacterial endocarditis, probably

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Fig. I. Case I: Myxoma in right ventricular outflow tract. The ultrasonic beam was scanned from the aortic root (AO) to the pulmonic valve (PV) to examine the right ventricular outflow tract. Tumor echoes (T) are present throughout the cardiac cycle in front of the pulmonary valve but are confined to diastole in front of aortic recording. ECG. Electrocardiogram. involving a mildly stenotic pulmonary valve with valve incompetence . The patient was treated with 2 million units of intravenous penicillin a day for 4 weeks and streptomycin , I Gm. a day intramuscularly, for 2 weeks and then 500 mg. a day for the final 2 weeks. She became afebrile in 24 hours and her general condition improved rapidly. An echocardiogram was nondiagnostic , but during some of the recordings of the pulmonary valve an ill-defined structural echo was seen to move anteriorly in diastole and posteriorly in systole in front of the pulmonary valve . The patient remained well and active after discharge and returned to work . Eight subsequent blood cultures were sterile, but the sedimentation rate remained at 35 mm. per hour. The murmurs remained essentially unchanged and a repeat echocardiogram on March IS, 1976, clearly showed a tumor in the outflow tract of the right ventricle (Fig. I) . The patient was therefore admitted for cardiac catheterization. On March 23 cardiac angiography with injection of contrast material into the superior vena cava in the posteroanterior and right anterior oblique projections revealed a large tumor in the right ventricular outflow tract prolapsing through the pulmonary valve during systole and back into the right ventricle during diastole . Several injections of indocyanine green in the right atrium revealed no left-to-right shunt. The operation was undertaken on March 31. A large gelatinous tumor (5 by 4 by 2 em) was found attached by a stalk to the anterolateral wall of the right ventricular infundibular chamber. There were two polypoid projections on the tumor, each about 2.5 em . in length and I em . in maximal thickness . One contained a soft fibrinous vegetation at its tip and projected into the main pulmonary artery in systole . The anterior cusp of the pulmonary valve had a central perforation; the right cusp was almost completely destroyed. whereas the posterior (left) cusp appeared to be normal. Both the ventricular septum and tricuspid valve were normal. The tumor, its stalk, and a small portion of the right ventricular wall were resected. Since the operation the patient has remained asymptomatic and has returned to work. There is a systolic ejection click in the pulmonary area as well as a murmur of pulmonary in-

Fig. 2. Case I. Vegetation at the tip of the myxoma with clumps of cocci embedded deepl y in the fibrinou s material. (Hematoxylin and eosin ; orig. mag . x IS.)

sufficiency. Several repeat echocardiograms have shown complete disappearance of abnormal echo complexes. An echocardiogram of the patient's only brother showed no abnormalities . Pathological examination. Microscopic sections showed a poorly cellular tumor with an abundant myxomatous matrix. The component cells varied from spindle-shaped . fibroblastlike cells to large stellate forms. The muco id stroma was rich in mucopolysaccharides as demonstrated by a special stain (alcian blue) . The vegetation was closely adherent and almost incorporated into the tip of the myxoma. It was composed largely of fibrin with focal accumulation of polymorphonuclear leukocytes with small deposits of calcium. Clusters of Gram-positive coccal micro-organisms were deeply embedded in the vegetation and covered by a relatively thick layer of fibrin (Figs. 2 and 3). CAS E 2. The 48-year-old father of Patient I had been in excellent health until June, 1976, when he began having fatigue, malaise, and a sore throat. Several days later he developed severe pleuritic chest pain associated with upper abdominal pain and was hospitalized at another institution. The diagnosi s of pulmonary embolism was made on the basis of an abnormal perfusion lung scan. He was treated with

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Fig. 3. Case I. Clumps of coccal microorganisms embedded in fibrinous vegetation. (Hematoxylin and eosin; orig. mag. x 2oo.) anticoagulants and then referred to the Genesee Hospital on July 27, 1976, for further evaluation. On examination he was afebrile, the pulse rate was 76 beats per minute and regular, and the blood pressure was 140/85 mm . Hg . There was a soft late systolic murmur slightly accentuated by the Valsalva maneuver, but findings from the rest of the physical examination were unremarkable . The chest roentgenogram and electrocardiograms showed no abnormalities . The echocardiogram revealed prolapse of the mitral valve but no other structural abnormalities. The patient remained well on long-term anticoagulant therapy until May 16, 1977, when he was readmitted to the hospital for evaluation of a transient episode of slurred speech, marked incoordination of the arms, and confusion . He was afebrile, the pulse rate was 75 beats per minute and regular, and the blood pressure was 135/85 mrn, Hg. The cardiac impulse was normal, and on auscultation there was a midsystolic click followed by a very soft late systolic murmur at the apex . There was slight weakness of the left comer of the mouth , slight pronation drift of the left arm on posture holding, and a positive left Babinski response . Findings from the rest of the physical examination were unremarkable. The chest roentgenogram and electrocardiograms showed no abnormalities. Laboratory data. The hematocrit value was 36 percent. The white blood count. urinalysis , BUN, serum electrolytes, total proteins , and protein electrophoresis all were within normal limits. Sedimentation rate (Westergren) was 50 mrn. per hour. Lupus erythematosis preparation was negative and antinuclear factor was nonreactive . A spinal tap revealed normal pressure and spinal fluid. Results of skull roentgenograms, electroencephalogram, echogram, and brain scan all

were normal. Computerized axial tomography (CAT scan) of the brain revealed a low-density lesion in the region of the caudate nucleus, extending to the frontal hom of the lateral ventricle, which was highly suggestive of a small infarct. Mvmode and cross-sectional echocardiograms revealed a large mass in the right atrium and mitral valve prolapse (Figs . 4 and 5) . Cardiac catheterization on May 19, 1977, showed no evidence of a right-to-Ieft or left-to-right shunt, as determined by the injection of indocyanine green into the right atrium . Right atriograms, performed in the anteroposterior and right anterior oblique projections, revealed a large tumor in the right atrium attached to the interatrial septum and prolapsing through the tricuspid valve . The operation was undertaken on May 24. The right atrium was virtually filled with a fibrogelatinous mass attached by a stalk to the interatrial septum on the lateral aspect of an atrial septal defect (ASD) 2 cm. in diameter. The tumor and part of the atrial septum were excised and the interatrial septum was repaired . A second tumor (1.5 em . in diameter) was also noted on the Eustachian valve of the inferior vena cava , and this also was excised . The postoperative course was uncomplicated and the patient has remained asymptomatic . Two repeat echocardiograms have shown persisting mitral valve prolapse without other abnormalities. Echocardiograms of the patient 's two sisters showed no abnormalities. Pathological examination. The atrial tumor was poorly to moderately cellular with an abundant myxomatous stroma. The component cells were spindle shaped and elongated, round and small , or occasionally moderately large and multinucleated . The majority of the cells were uniform , with only focal pleomorphism and no mitotic activity . With special stains the stroma was shown to contain abundant mucopoly-

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RES ECG Fig. 4. Case 2: Right atrial myxoma. Preoperative study. A scan from the mitral valve (MV) to the tricuspid valve (TV) reveals a mass of echoes behind the tricuspid valve in diastole arising from a right atrial myxoma. The atrial

septum (AS) appears to be thickened, probably owing to the tumor stalk attached in this area. The mitral valve shows sagging in systole, indicative of mitral valve prolapse. RES, Respiration. ECG, Electrocardiogram.

Fig. 5. Case 2: Preoperative study. The two-dimensional echocardiogram (left) and the schematic anatomic explanation of the sector image (right) show a large tumor(T) in the right atrial cavity (RA). Atrial and ventricular septa are incompletely recorded because of dropouts. The two-dimensional recording was obtained by placing a mechanical sector scanner over the cardiac apex to view all four cardiac chambers in a horizontal plane. A, Anterior. P, Posterior. R, Right. L, Left. RV, Right ventricle. LV, Left ventricle. LA, Left atrium. RA, Right atrium. saccharides with a positive reaction for mucin (alcian blue and mucicarmine stains). The tumor at the inferior vena cava was histologically similar.

Discussion This family study illustrates several important clinical features of cardiac myxomas. Familial incidence. There are four previous reports of familial myxoma':" (Table I). Three of these case studies described cardiac myxomas restricted to sib-

lings; only one involved a parent and child, with atrial myxomas in a mother and three (all sons) of her seven children." Our report therefore represents the second description of familial myxoma involving both parent and child and the first father and daughter occurrence (Table I). Familial myxomas may be single or multiple and have been documented in the right and left atria, right ventricle, and pulmonary ring.":" Genetic transmission is the most probable explanation for the familial occurrence of cardiac myxoma, and the documenta-

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Table I. Familial myxoma Ref. No.

YS

1 2

MY

..

~ "

I

Involved family members

3

Brothers* Brothers Brotherandsister

4

Four brothers*

5

Mother, three sons

....." '-

Fig. 6. Case 2: Postoperative study. The tricuspid valve (TV) recording, on the right . shows disappearance of mass echoes from the right atrial tumor present in the preoperative study. The mitral valve (MV) tracing, on the left , continues to show evidence of mitral valve prolapse characterized by posterior displacement in late systole . CW , Chest wall. VS. Ventricular septum. ECG . Electrocardiogram.

tion of these tumors in a mother and three of her sons suggests a dominant mode of inheritance ." Unfortunately, our study with only one affected sibling does not further clarify the mechanism of transmission except for excluding sex-linked recessive inheritance. The temporal proximity of symptoms in the father and daughter raises the possibility of environmental etiologic factors such as viral infection, as suggested by Burch and associates. 7 Infected myxoma. Cardiac myxomas often are associated with a general constitutional reaction characterized by fever, malaise, weight loss, anemia, high sedimentation rate, and abnormalities of serum proteins suggesting the possibility of a systemic disease or an infection , such as bacterial endocarditis. Rarely, a myxoma actually becomes infected; there are only seven such documented cases involving a variety of microorganisms (six in the left atrium and one on the pulmonary ring) (Table 11).1 . 8 -13 The echocardiogram has provided a useful noninvasive means for detecting cardiac myxomas. However , the precise clinical diagnosis is not always possible because echocardiographic manifestations are variable and large vegetations;'! an infected thrombus;" or even mitral valve prolapse" sometimes may produce patterns indistinguishable from atrial myxomas. Consequently, the unequivocal echocardiographic demonstration of a mobile intracardiac mass associated with neurologic deficits should be considered a dangerous situation requiring urgent operation regardless of the cau se . 13

Present

Father, daughter

report

I

Site

Left atrium; pulmonaryvalve ringt Left atrium; right atrium Right atrium (male); left atrium (female) Left atrium (male); and right ventricle and left atrium (rnaler t: right ventricle and left atrium (male); right ventricle. left atrium , and two in right atrium (male) Biatrial mass (female); left atrium (male); left atrium (male); right atrium (male) Two in right atrium (male); right ventricle (female)

'Same family. t Same patient.

As in valvular bacterial endocarditis , the timing of the operation in a potentially infected area poses a difficult problem. We believe that an infected left atrial myxoma should be resected as soon as the diagnosis is made to avoid catastrophic embolic complications. All six of the previously reported patients with infected left atrial myxomas presented with major neurological events. v " Interestingly, in all these cases there was no significant damage to the mitral valve, which was spared by both the tumor and the infective process . Thus we conclude that an infected left atrial myxoma can be resected successfully in most cases without mitral valve replacement. In contrast, the two patients with infected right ventricular myxomas exhibited major destruction of the pulmonary valve . The patient described by Krause and associates I required pulmonary valve replacement, but our patient has remained hemodynamically stable despite destruction of two cusps of the pulmonary valve. The greater degree of destruction with infected right-sided myxomas may be due to the presence of s uperi mposed valvular endocarditis , pos sibly because the absence of systemic embolization delays the diagnosis. Krause 's patient had bacterial involvement of the pulmonary valve whereas our patient did not, perhaps because a course of antibiotic therapy had eradicated valvular endocarditis. Cardiac myxomas may be associated with valvular injury . Carter and colleagues , 17 in a pathological study of endocardial lesions in patients with myxoma, demonstrated microscopic valvular changes which they attributed to friction . Sterile , calcified right and left atrial myxomas (reflecting chronicity of the disease process )

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Table II Ref.

No.1

Sex, age

I

Bacteriology (including hlood cultures)

I

Diagnostic method

I

Site ofmyxoma

Clinical presentation

8

M, 39

Staphylococcus aureus; Candida parapsilosis

Autopsy

Left atrium

Cerebrovascular accident

9

M,48

Streptococcus faecalis

Autopsy

Left atrium

Febrile illness and cerebral embolus

10

F, 50

Streptococcus viridans; Staphylococcus alhus

Angiography

Left atrium

Cerebral embolus

M, 34

Staphylococcus epidermidis

Angiography

Pulmonic ring

Right-sided failure; constitutional symptoms

II

F, 17

Staphylococcus aureus*

Angiography

Left atrium

12

F, 48

Staphylococcus aureus

Echocardiography

Left atrium

Bacterial endocarditis; congestive cardiac fai lure; cerebrovascular accident Febrile illness with cerebral embolus

13

F, 48

Histoplasma capsulatum

Echocardiographyt Left atrium

Fever and constitutional symptoms

Present report

F, 19

Streptococcus viridans

Echocardiography

Constitutional illness

Right ventricle

Valve damage, tumor calcification, tissue cultures Mitral valve thickened with fused chordae; myxoma not calcified; fungi found on surface of tumor Normal mitral valve; invasion of tumor by microorganisms; myxoma not calcified Mitral valve normal; microscopic calcification; Grampositive cocci observed near area of attachment to atrial wall; Streptococcus viridans cultured from tissue within the tumor Pulmonary valve destroyed; Myxoma not calcified; tumor cultures grew Staphylococcus epidermidis Dilated mitral anulus; Myxoma calcified; no microscopic examination reported Normal mitral valve; myxoma not calcified; microabscess formation was noted but no organisms were identified No calcification; superimposed thrombus revealed branching hyphae and budding yeast forms of Histoplasma capsulatum Pulmonary valve destruction; myxoma not calcified; small clusters of Grampositive cocci lying deep in vegetation on surface of tumor

'Exact site of endocarditis uncertain. tEvidence of disseminated histoplasmosis. Infection on myxoma diagnosed at operation.

have been shown to cause gross damage to the tricuspid and mitral valves, respectively, by the so-caIled "wrecking ball" effect. 18. 19 Paradoxical embolism. The father with the right atrial myxoma presented a clinical picture (including the CAT scan) highly suggestive of paradoxical embolism through an ASD. The association of right atrial myxomas with right-to-Ieft shunting through an ASD or patent foramen ovale is widely known.f" Some reports have described clinical phenomena compatible with paradoxical embolism, but so far none has provided definite pathological proof of this complication.f"?"

We believe that our patient sustained a paradoxical embolus despite normal right atrial pressure and no demonstrable right-to-Ieft shunting at rest. At operation the right atrial myxoma was protruding into the left atrium through an ASD, and it is therefore conceivable that an inadvertent Valsalva maneuver triggered paradoxical embolism. In this respect, Cheng'" documented that the Valsalva maneuver causes a momentary increase of right atrial pressure above the left atrial pressure with consequent reversal of the normal interatrial gradient, which may result in right-to-Ieft shunting across a patent foramen ovale.

788 Powers et al.

Association of right atrial myxoma, mitral valve prolapse and ASD. There appears to be an association between right atrial myxoma and ASD. 25. 26 Recently two cases of coexisting cardiac myxoma and mitral valve prolapse were reported.": 28 Mitral valve prolapse in the case reported by DeMaria and associates'" was probably due to the mechanical effect of a left atrial myxoma, because prolapse ceased after resection of the tumor. The case of Myers and co-workers'" was identical to ours, with a right atrial myxoma and persisting mitral valve prolapse after resection of the tumor. We believe that our patient is the first known patient with the combination of right atrial myxoma, mitral valve prolapse, and a true ASD (rather than a patent foramen ovale). The known association of mitral valve prolapse with ASD,29 myxoma and ASD,25. 26 the recently documented association of myxoma with mitral valve prolapse;" and the combination of all three in our patient pose interesting questions concerning embryogenesis. We are indebted to Dr. M. M. Salinsnjak for the pathological examination of the surgical specimens. REFERENCES

2 3 4

5

6

7 8

9

IO II

Krause S, Adler LN, Reddy PS, Magovern GJ: Intracardiac myxoma in siblings. Chest 60:404-406, 1971 Klied n, Klugman J, Haas J, Battock D: Familial atrial myxoma. Am J Cardiol 32:361-364, 1973 Farah MG: Familial atrial myxoma. Ann Intern Med 83:358-360, 1975 Liebler GA, Magovern GJ, Park SB, Cushing WJ, Begg FR, Joyner CR: Familial myxoma in four siblings. J THORAC CARDIOVASC SURG 71:605-608, 1976 Siltanen P, Tuuteri L, Norio R, Tala P, Ahrenberg P, Halonen PI: Atrial myxoma in a family. Am J Cardiol 38:252-256, 1976 Nanda NC, Barold SS, Gramiak R, Ong LS, Heinle RA: Echocardiographic features of right ventricular outflow tumor prolapsing into the pulmonary artery. Am J Cardiol 40:272-276, 1977 Burch GE, Shewey LL, Harb JM: Coxsacke B4 viruses and atrial myxoma. Am Heart J 88:634-639, 1974 Dick HJ, Mullin EW: Myxoma of the heart complicated by bloodstream infection by Staphylococcus aureus and Candida parapsilosis. NY State J Med 56:856-859, 1956 Rae A: Two patients with cardiac myxoma-one presenting as bacterial endocarditis and one as congestive cardiac failure. Postgrad Med J 41:644-648, 1965 Malloch CI, Abbott JA, Rapaport E: Left atrial myxoma with bacteremia. Am J Cardiol 25:353-358, 1970 Selzer A, Sakai FJ, Popper RW: Protean clinical manifestations of primary tumors of the heart. Am J Med 52: 9-18, 1972

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12 Graham HV, von Hartitzch B, Medina JR: Infected atrial myxoma. Am J Cardiol 38:658-661, 1976 13 Rogers EW, Weyman AE, Nobler J, Bruins SC: Left atrial myxoma infected with Histoplasma capsulatum . Am J Med 64:683-690, 1978 14 Feigenbaum H: Echocardiography , Philadelphia, 1976, Lea & Febiger, Publishers, p 447 15 Malcom AD, Chaput de Saintonage DM: Infected left atrial mass within anatomically normal heart. Thorax 30:693-696, 1975 16 Chandraratna PAN, Langevin E: Limitations of the echocardiogram in diagnosing valvular vegetations in patients with mitral valve prolapse. Circulation 56:436-438, 1977 17 Carter JB, Cramer R, Edwards JE: Mitral and tricuspid lesions associated with polypoid atrial tumors, including myxoma. Am J Cardiol 33:914-919, 1974 18 Harvey WP: Clinical aspects of cardiac tumors. Am J Cardiol 21:328-343, 1968 19 Nasser WK, Davis R, Dillon J, Tavel ME, Helmen CH, Feigenbaum H, Fisch C: Atrial myxoma. Clinical and pathological features in nine cases. Am Heart J 83: 694-704, 1972 20 Goldschalger A, Popper R, Goldschalger N, Gerbode F, Prozan G: Right atrial myxoma with right to left shunt and polycythemia presenting as congenital heart disease. Am J Cardiol 30:82-86, 1972 21 Coates EO Jr., Drake EH: Myxoma of the right atrium, with variable right to left shunt. Clinical and physiological observations and report of a case with successful operative removal. N Eng1 J Med 259:165-169, 1968 22 Belle MS: Right atrial myxoma. Circulation 19:910-917, 1968 23 Heath D: Pathology of cardiac tumors. Am J Cardiol 21:315-327, 1968 24 Cheng TO: Paradoxical embolism. A diagnostic challenge and its detection during life. Circulation 53:565-568, 1976 25 Marpole DGF, Kloster FE, Bristow 10, Griswold HE: Atrial myxoma. A continuing diagnostic challenge. Am J Cardiol 23:597-602, 1969 26 Symbas PN, Abbott OA, Logan WD, Hatcher CR: Atrial myxomas. Special emphasis on unusual manifestations. Chest 59:504-510, 1970 27 DeMaria AN, Vismara LA, Miller RR, Neuman A, Mason DT: Unusual echocardiographic manifestations of right and left heart myxomas. Am J Med 59:713-720, 1975 28 Meyers SN, Shapiro JE, Barresi V, BeBoer AA, Pavel 01, Gracey DR, Suhre DE, Buehler JH: Right atrial myxoma with right to left shunting and mitral valve prolapse. Am J Med 62:308-314, 1977 29 Pocock WA, Barlow 18: An association between the billowing posterior mitral leaflet syndrome and congenital heart disease, particularl y atrial septal defect. Am Heart J 81:720-722, 1971