Studies on magnesium's mechanism of action in digitalis-induced arrhythmias.

The mechanism by which magnesium affects digitalis-induced arrhythmias was studied in dogs with and without beta-receptor blockade. Digoxin was infused at a rate of 2.5mug/kg/min until ventricular tachycardia developed, then half the animals were given MgSO4, the other half saline. In animals given MgSO4, sinus rhythm was immediately re-established; in animals given saline, ventricular tachycardia persisted. In animals with beta-receptor blockade, MgSO4 was as effective in abolishing ventricular tachycardia as in those without beta-receptor blockade. We found no evidence that magnesium re-activated digoxin-inhibited (Na+, K+)-ATPase, altered myocardial or microsomal digoxin binding, or acted via the autonomic nervous system. Magnesium's direct effect on calcium and potassium fluxes across the myocardial cell membrane may be the mechanism of its antiarrhythmic action in digitalis-toxic arrhythmias.

The status of cardiac transplantation, 1975.

Since December 1967, 263 human cardiac transplant operations have been performed throughout the world. Eighty-two of these were performed at Stanford University Medical Center, In 1974, 27 such operations were performed, 15 at Stanford Survival rates for the entire Standford series are 48% at one year and 25% at three years; survival rates at one and three years for patients surviving the first three critical months after transplantation are 77% and 42%, respectively. Recipients under the age of 55 years, with New York Heart Association Class IV cardiac disability, are selected for transplant procedures according to criteria dictated by experience over the past seven years. A routine immunsuppressive regimen for organ transplantation, incorporating prednisone, azathioprine, and antithymocyte globulin is employed early postoperatively, and prednisone and azathioprine are used for indefinite maintenance therapy. Acute cardiac graft rejection in nearly all recipients is diagnosed by clinical signs, electrocardiographic changes, and percutaneous transvenous endomyocardial biopsy. Ninety-five percent of acute rejection episodes are reversible with appropriate immunosuppressive treatment, but infectious complications are common and have accounted for 56% of all postoperative deaths. The Stanford experience in cardiac transplantation has demonstrated the potential therapeutic value of this procedure. Maximum survival now extends beyond five years. Satisfactory graft function has been documented in long-term surviving patients, the majority of whom have enjoyed a high degree of social and physical rehabilitation.