118 Abstracts

@IO 14.6) afflicted with a hereditary myopathy.

Over 90% of 653 myopathic hamsters, examined at

autopsy between 90 and 164 days of age. revealed

chronic passive venous congestion, while 8 of the re-

maining animals were nonedematous and showed

asymmetric left ventricular hypertrophy resembling

muscular subaortic stenosis. In subsequent studies,

concurrent administration of norepinephrine (0.08

mg.jlOO gm. body weight, three times daily, sub-

cutaneously) and thyroxine (0.05 mg./lOO gm. body

weight two times daily, subctitaneously) given con-

tinuously for eight weeks elicited muscular subaortic

stenosis, with predominant thickening of the upper

half of the free wall of left ventricle and the intraven-

tricular septum, in 60y0 of the myopathic hamsters;

injection of norepinephrine or thyroxine alone was in-

effective in this respect. Twenty animals were used in

each experimental group; treatments were initiated

at the age of 28 days.

While the progression of spontaneous myolysis was

not influenced by the hormone combination, heart

muscle lesions appeared to be an essential factor in the

genesis of asymmetric ventricular hypertrophy, since

identical treatment failed to induce this condition in

healthy hamsters.

The Effects of Digitalis on the Hemodynamic Re-

sponse to Intense Upright Exercise in Patients with

Mitral Stenosis, G. D. BEISER, M.D., S. E. EPSTEIN,

M.D., M. STAMPFER, M.D., B. F. ROBINSON, M.D. and

EUGENE BRAUNWALD, M.D., F.A.c.c., Bethesda, Md.

Although digitalis is often administered to sympto-

matic patients with mitral stenosis (MS) regardless

of rhythm, it is not known if this drug actually im-

proves their circulatory capacity. Accordingly, 8 pa-

tients with pure MS, 6 in normal sinus rhythm

(NSR) and 2 in atria1 fibrillation (AF) were studied

at rest and during intense treadmill exercise. Cardiac

index (CI), oxygen consumption (VO,) and mean pul-

monary arterial pressure (PAP) were measured in 6

patients before and after intravenous ouabain (0.01

mg./kg.); in 3 patients the effects of chronic digital-

iza tion with oral digoxin were studied. In the patients with NSR, ouabain did not increase

the CI achieved during intense exercise (control = 3.84, dig. = 3.63 L./min./M.2. p > 0.05); chronic

digitalization also produced no improvement (3.55

vs. 3.36 L./min./M.*). Similarly, acute and chronic digitalization did not alter the heart rate (HR), 132

vs. 131, PAP, 62 vs. 61 mm. Hg, and iiOz, 488 vs.

445 ml./min./M.“. In MS and AF, when ouabain

produced only minimal cardiac slowing (160 to 152), CI was unchanged (3.16 vs. 3.14); when a large de- crease in HR was produced (172 to 148), a 20% in- crease in CI occurred (3.36 to 4.18).

‘I‘hus it is concluded that the pumping capacity of the heart during exercise in patients with MS and

NSR is not improved by digitalis. Consequently, it

appears that there is no physiologic basis for the

administration of digitalis to such patients.

The Vectorcardiographic Evolution of Left Ven-

tricular Hypertrophy, HUBERT BELL, M.D., DAVID

PUGH, M.D. and MARVIN DUNN, M.D., F.A.c.c., Kansas

City, Kans.

Pruitt has suggested that the electrocardiographic

manifestations of left ventricular hypertrophy are due

to a conduction disturbance rather than to hyper-

trophy per se. In a review of 2,800 vectorcardiograms,

23 had abnormal loop rotation of the vector in all

three planes associated with evidence of incomplete

left bundle branch block and left ventricular hyper-

trophy. All 23 tracings were from patients with

severe aortic valvular disease who had no evidence of

associated myocardial infarction. Autopsy confirma-

tion of aortic stenosis and left ventricular hyper-

trophy was present in 5 cases. Cardiac catheterization

data were available in 8 additional cases. In 4 pa-

tients, the gradual development of abnormal rotation

in all three vector planes was demonstrated on serial

vectorcardiograms as their aortic disease became more

severe. The configuration of the vector loops followed

a predictable evolution through five stages of develop-

ment that correlated with the hemodynamic severity

of the aortic lesion. The scalar tracings demonstrated

evidence of left ventricular hypertrophy of increasing

severity.

In 5 patients there was a rapid return of normal

rotation of the vector loop in all three planes following

corrective aortic valve surgery. The scalar tracings

also showed a rapid return toward normal. The

rapidity of these changes suggests that both the abnor- mal direction of depolarization and the evidence of

left ventricular hypertrophy are due to conduction

disturbance.

Pacing During Selective Coronary Angiography:

A Method of Reducing the Hazards of the Pro-

cedure, ALBERTO BENCHIMOL, M.D., F.A.C.C. and

EDWARD M. MCNALLY, M.D., La Jolla, Calif.

One of the effects of injecting radiocontrast mate-

rial into the coronary circulation is a fall in heart rate

due to sinus slowing. This slowing is associated with a decrease in coronary and aortic pressures which in

many cases exceeds 40y0 of the preinjection levels.

These pressure changes are largely obviated by pacing

the heart at its preinjection rate. This bradycardia and its attendant hemodynamic phenomena occur at a time when the myocardium has been made ischemic

by the displacement of blood from the coronary tree

THE AMERICAN JOURNAL OF CARDIOL.OGY