ABSTRACTS

given aortographic grades and had a slightly closer re- lation between regurgitant flow and grade (no. = 37, r = 0.73, P <O.Ol). However, no significant improve- ment in correlations occurred in subgroups of patients with ejection fraction <0.55 (no. = 32, r = 0.57, P <O.Ol>, or with end-diastolic volumes >lOO ml/m2 (no. = 45, r = 0.66, P <O.Ol), or with no associated aortic valve systolic pressure gradients >20 mm Hg (no. = 56, r = 0.67, P <O.Ol), or when the regurgitant flow was expressed as percent of left ventricular flow (no. = 69, r = 0.56, P <O.Ol). This study reveals the inac- curacies inherent in estimating the severity of aortic insufficiency by aortography.

Prevalence of Hypomagnesemia in a Prospective Clinical Study of Digitalis Intoxication

GEORGE A. BELLER, MD; WILLIAM B. HOOD, Jr., MD; THOMAS W. SMITH, MD; WALTER H. ABELMANN, MD, FACC; WARREN E. C. WACKER, MD, Boston, Massachusetts

That hypomagnesemia might contribute to the develop- ment of digitalis toxicity has been Suggested. Of 931 consecutive admissions over 8 months to a single medi- cal service, 135 patients were taking digitalis on entry, and of these toxicity was shown by serial electrocardio- grams in 39 cases (29%). Four additional patients be- came toxic during hospitalization. There were signifi- cantly higher serum drug concentrations (digoxin or digitoxin) in toxic than in nontoxic patients. No differ- ence was found between the 2 groups with respect to serum sodium, chloride or CO,.

Serum magnesium (Mg) determinations (normal range 1.76-2.44 mEq/liter) were performed on coded sera frdm toxic and nontoxic patients. Hypomagnesemia (Mg <1.76 mEq/liter) was present in 37% (14 of 38) of toxic and 21% (17 of 82) of nontoxic patients (0.05 .<P <&lo). When normokalemic (potassium [K] >3.5 mEq/liter) patients in the 2 groups were compared, there was still a greater prevalence of hypomagnesemia in toxic (37.5%) than in nontoxic (19.5%) patients (0.05 <P <O.lO). Seventy-nine percent of toxic hypo- magnesemic patients were taking diuretics, whereas 58 percent of toxic patients with normal or high Mg levels were receiving diuretics (nonsignificant). The percent- age of patients with hypermagnesemia (Mg >2.44 mEq/liter) was significantly greater in toxic (16%) than in nontoxic (1.2%) patients (P <O.Ol) and was correlated with the higher mean serum creatinine level in the former group, 3.4 2 1.2 (standard deviation) mg/lOO ml versus 1.5 -C 0.6 mg/lOO ml (P <0.02).

This study shows a high prevalence of hypomagnese- mia exists in patients with digitalis toxicity. The po- tential value of magnesium supplementation in the prophylaxis or therapy of digitalis intoxication war- rants investigation.

Systolic Time Intervals in Acute Myocardial Infarction

E. D. BENNETT; CHARLES S. SMITHEN, MD; G. E. SOWTON, MD, London, England

Systolic time intervals were measured in 24 patients

with acute myocardial infarction and compared to nor- mal values predicted for heart rate and sex. Pulmonary arterial pressures were measured in 18 patients, and cardiac output, using the Fick technique, in 10 patients. In all patients the Q-S2 interval (total electromechani- cal systole) was short during the acute episode. This shortening in the Q-S2 interval was due entirely to a reduction in left ventricular ejection time (LVET) (r = 0.72; P <O.OOl) with no change in the pre-ejection period. The mean deviation from normal of the Q-S2 interval was 27 & 3.6 msec in patients with an uncom- plicated clinical course, and was 52 + 4.7 msec in pa- tients with a complicated course, the difference being significant at the 1% level. Those patients with the highest pulmonary arterial diastolic pressure tended to have the shortest Q-S2 intervals. (r = -0.58; P <O.Ol). There was no relation between stroke volume and the deviations in the Q-S2 and LVET intervals, It is concluded that the Q-S2 interval is short in patients with acute myocardial infarction and that this is due to a reduction in LVET. Since heart rate, stroke volume and mean aortic pressure did not account for the changes found, increased catecholamine liberation may explain our findings.

Emergency Management of Pacemaker Failure by Means of Externally Applied Radiofrequency Energy

RICCARDO BENVENUTO, MD, FACC; PETER S. MAYER, MD, Chicago, Illinois

Pacemaker failure due to premature battery depletion is an emergency situation requiring immediate correc- tion. Current techniques used to cope with this prob- lem require either a rapid surgical exteriorization of the failing pulse generator or the insertion of a tem- porary transvenous pacemaker catheter for interim pacing. Both methods are time-consuming and have other undesirable features. Radiofrequency energy stimulation of the failing pulse generator has been used routinely by us to solve this problem. The failing pulse generator is activated through the intact skin by means of a radiofrequency antenna placed on the skin over the failing pacemaker. Bursts of radiofrequency energy are produced by a high energy generator and transmitted to the pulse generator where existing cir- cuitry acts as the receiver. Augmentation of the weak pacemaker impulse is thus achieved, and resumption of effective pacing will occur. With this technique an in- herently emergency situation is converted into an elec- tive procedure without crisis. To date this method has been employed in 6 patients, and in all effective pacing was reestablished and maintained until a routine pulse generator replacement could be carried out. The possi- bility of making the radiofrequency transmitter avail- able to all patients with implanted pacemakers as a means of controlling unexpected battery depletion when medical help is unavailable is anticipated. Additional uses of the radiofrequency unit in the diagnosis and treatment of other forms of pacemaker failures are de- .scribed.

VOLUME 26, DECEMBER 1970 625