Abstracts 119

The major advantage of homograft replacement of the aortic valve appears to be virtual elimination of postoperative embolic complications. Anticoagulant therapy has not been used, thus eliminating the incon- venience and complications associated with such

therapy. Most of the homografts used in this series were sterilized in betapropiolactone solution and stored in a balanced salt solution. More recently the homografts used have been preserved frozen and sterilized by radiation; this method is considered better.

At present, an aortic valve homograft is the valve of choice when replacement is required in isolated aortic valve disease. This procedure probably is not indi- cated in patients with severe aortic valve incompe- tence secondary to dilatation of the aortic root or in those in whom satisfactory coronary artery perfusion cannot be performed.

Long-Term Management of Chronic Tachycardias

of Childhood with Orally Administered Propra-

x10101. LINDA WALTERS, M.D., LEONDARD S. GEPTES, M.D., JACQUELINE A. NOONAN, M.D. and BORYS SURAWICZ, M.D., F.A.C.C., Lexington, Ky.

Chronic tachycardias of childhood are uncommon and difficult to treat. However, treatment is indi- cated because of the risk of heart failure. The effec- tiveness of long-term propranolol therapy in the adult prompted the use of propranolol in the treatment of 5 children, aged 4 to 13 years, with chronic supraven- tricular tachycardia, of four months’ to nine years’ duration, which was unresponsive to digitalis. In 3 children the onset of the tachycardia was associated with myocarditis complicated by congestive heart failure. In 1, heart failure without documented myocarditis occurred as a result of the tachycardia. The chronic tachycardia was ectopic atria1 in 3 and sinus in 2. We have treated these children with 20 to 120 mg. of orally administered propranolol per day, alone and in combination with digitalis, for as long as 12 months. Although propranolol alone slowed the resting and exercise heart rates in 3 of 4 children treated, the combination of digitalis and propranolol was more effective and slowed the rates in all 5. The results are summarized as follows:

Heart Rate (beats/min.) 2-Step

Exercise Therapy Rest (3 min.)

None 120-180 160-216 Digitalis alone 110-180 14&200 Propranolol alone 110-140 140-160 Propranolol + digitalis 80-l 30 110-150

VOLUME 21, JANUARY 1968

In 1 child, slowing of the rate was due to suppres- sion of the ectopic rhythm. In the others, slowing occurred without a change in rhythm. Propranolol produced no undesirable effects. Our results demon- strate that long-term treatment with propranolol, particularly in association with digitalis, slows the heart rate in children with chronic tachycardias resistant to digitalis alone. We have concluded that propranolol is a valuable adjunct in the therapy of the chronic tachycardias of childhood.

Plasma Digitoxin Levels and Left Ventricular

Ejection Time After a Digitalizing Dose of Digi-

toxin. WILLIAM S. WILSON, M.D., JAMES TOLBERT,

B.S., and WALTER DIGIULIO, M.D., New Brunswick, N. J., and Ann Arbor, Mich.

Nine informed volunteers without cardiac disease were given 0.8 mg. digitoxin intravenously followed by another 0.4 mg. intravenously in four hours. The left ventricular ejection time was recorded from the external carotid pulse, and venous blood was sampled two hours after the last dose of digitoxin and daily for five days. The plasma was assayed for digitoxin by measuring in duplicate the inhibition of the uptake of radioactive rubidium by human red cells incubated in a methylene dichloride extract of plasma, by minor modifications of the technic of Lowenstein.

Five subjects showed a significant reduction in rate- corrected left ventricular ejection time, maximal 12 to 24 hours after digitalization, and present until at least the third day. In 4 subjects, digitalization had no effect on the rate-corrected left ventricular ejec- tion time, despite efforts to obtain a basal state.

The plasma digitoxin levels were highest two hours after digitalization was completed (mean 39 mpg./ ml.) and were 30 mhg./ml. one day after digitaliza- tion. The levels declined slowly with a half-life of approximately three and one-half days.

This study demonstrates a relation, although imper- fect, between the physiologic effect and the plasma level of digitoxin. The early maximal plasma level before the onset of maximum physiologic effect is thought to be secondary to slow plasma-tissue equili- bration. The plasma half-time of digitoxin is slightly less than the physiologic half-time previously re- ported by others. The estimation of plasma digi- toxin yields reproducible results that may prove of value in a variety of clinical and investigative situa- tions.

Studies in Immunity to Serum Cholesterol and

Atherosclerosis. PAUL L. WOLF, M.D., HOWARD

BLUME, BARBARA TWARKOWSKI, M.T. and JONATHAN

CHUA, PH.D., Detroit, Mich.

We have recently instituted experiments to attempt