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\I ~IICI 1011 01 the immunologic competence of the lto\t ;~nd rhe life-threatening and restricting com- I)lic .11 ion5 of immunosuppressive therapy.

Prevalence of Congenital Heart Defects Among Offspring of Parents with Congenital Heart Dis- ease. J. J. NORA, nr.~., F.A.c.c., PAUL F. DODD, lr.n., R. D. LEACHMAN, M.D., F.A.c.c., R. J. SOM- \II,RVILLE, h1.D.. F..~.c.c. and D. G. MCNAMARA, \T.I).. F.A.~.c., Houston, Texas.

‘I-he answers to 2 questions were sought in this investigation: (1) For purposes of genetic coun-

seling what is the empiric risk to offspring of a parelit who has a congenital heart lesion? (2) Do the data meet the predictions of the multifac- torial inheritance hypothesis for the cause of con- genital heart diseases? Two lesions were studied: atria1 septal defect (ASD) and ventricular septal defect (VSD). The index subjects were in the re- productive age and over the mean national age for marriage (women over 21, men over 25 years of age) and had received surgical correction in the past or were currently hospitalized for cardiac catheterization or surgery. All children were per- sonally examined, and appropriate diagnostic stud- ies were performed. One hundred and sixty-seven patients with ASD were ascertained; 112 were married and 62 had children. Of the 191 children, 5 (2.6%) had congenital heart lesions, most often ASD. One hundred and forty-one patients with VSD were ascertained; 96 were married and 57 had children. Of the 162 children, 6 (3.7%) had congenital heart lesions, usually VSD. The answers to the questions posed were: (1) The empiric risks of affected offspring-2.6% for parents with ASD and 3.7% for parents with VSD-are 35 times the population incidence of ASD and 20 times the population incidence of VSD. (2) The data are consistent with the expectation of affected first degree relatives predicted by the multifactorial inheritance hypothesis for the cause of congenital heart diseases.

On the Relationship Between U Waves of the ECG and the Transmembraue Action Potentials of Single Myocardial Cells of the in situ Heart. Y. O~~URA, M.D. and D. LEHR., M.D., F.A.c.c., New York, N. Y.

The genesis of U waves of the ECG has re- mained obscure. Although correlation of the ECG with the corresponding transmembrane action po- tentials (TAP’s) of single cardiac cells of the intact heart could be expected to provide important information on the mechanisms of U wave forma-

VOLUME 23, JANUARY 1969

tion, little work has been done with this method- ology because of technical limitations. Using “flexi- bly mounted nonpolarizing flexible glass cal~illary microelectrodes” developed in this laboratory, we were able to carry out experiments on such corre-

lations in hearts of rabbits, guinea pigs and rats. The appearances of occasional transitional U waves following the intravenous administration of large doses of acetylcholine, heparin, cardiac glycosides, etc., were monitored. The following experimental findings appear of interest with regard to the genesis of U waves: (1) While many ventricular cells were firing TAP’s in normal se- quence, the TAP’s of some of these were excep- tionally long. (2) The beginning of the rapidly rising part (phase 0) of these prolonged TAP’s corresponded to an early part of the QRS com- plex, whereas the terminal portion coincided with the end of a U wave. (3) The peak point of the U wave corresponded approximately to the rapidly repolarizing part of phase 3 of the prolonged TAP. (4) Such abnormally long TAP’s seemed to occur predominantly in the area of the interventricular septum near the apex of the heart. (5) The dis- tance between the peak of the T wave and the peak of the U wave was directly proportional to the degree of prolongation of the corresponding TAP. With gradual reduction of the TAP pro- longation, the U wave approached the T wave, finally merging with the latter and forming a simple T with or without 2 clear peaks. It is con- cluded that the prolongation of the TAP is re- sponsible for the formation of certain types of U waves.

Auscultatory Manifestations of Isolated Bilateral Pulmonary Artery Stenosis-A Phonocardiographic, Hemodynamic, Angiographic Correlative Study. J. K. PERLOFF, M.D., F.A.C.C. and E. J. LEBAUER, M.D.. Washington, D. C.

Despite considerable interest in pulmonary ar- tery stenosis (PAS), a number of its clinical fea- tures remain ill defined. Accordingly, auscultatory, phonocardiographic, hemodynamic and angio- graphic observations were made in 10 patients with uncomplicated PAS. The purpose of these observations was to reexamine the acoustic signs and to comment on certain previously undescribed points regarding the second heart sound. Proximal pulmonary artery (PA) pressure pulses typically showed systolic hypertension (35 to 75 mm. Hg) with rapid falls to diastolic levels found in distal sites. Arterial gradients were therefore systolic and not diastolic, and accompanying murmurs