ABSTRACTS

patency of the vein graft in all but 2 subjects. Ven- tricular contractility including areas of dyskinesia and akinesia were unchanged. Cardiac output and left ven- tricular pressure data were improved in 12 of the sur- vivors.

ventricular extrasystoles (ES), and in 3 with atria1 fibrillation (AF). In 6 the left ventricle (LV), assessed by end-diastolic volume and pressure, ejection fraction and stroke volume, was normal (LVN) : 7 had dys- function (LVD). The following indexes were digitally computed from LV pressure (P) taped from catheter

Results of Aorta-Coronary Bypass Graft Surgery. tip manometers : peak dp/dt, dp/dt over developed pres-

Comparison with Arterial Implants and sure (DP) at DP of 40 mm Hg (dp/dt :DP = 40), the

Medical Treatment DP

G. K. SEHAPAYAK, MD; WALTER M.ALLISON, MD, FACC; DONALD G. PANSEGRAU, MD; JOHN C. GRAMMER, MD, FACC; WILLIAM L. KRAUS, MD, FACC*, Dallas, Texas

Data on all patients in our institution treated with aortocoronary saphenous vein bypass grafts before July 1970 were reviewed. Combined operations (with implants, aneurysmectomies, valve replacement) were excluded. This left 6’7 patients with single or multiple (mean 2.3) grafts (group I). Review of all coronary arteriograms before advent of bypass graft surgery yielded 64 patients who would have been candidates for bypass grafts by the criteria used in selecting group I. Of these, 31 had received arterial implants (group II), and 33 were treated medically (group III). The follow- ing indexes were statistically analyzed in all groups: age, sex, functional classification, severity of obstruc- tive disease, left ventricular ejection fraction and end- diastolic pressure, number of previous myocardial in- farctions and electrocardiographic Q waves. No signifi- cant differences were found, except in functional classi- fication (3.2 in group I, 2.6 in group III, P <0.05). Mortality for the medically treated patients (group III) was 15.3% in 1 year, 24.2% total, mean followup period 28 months. Results in the surgical groups are shown in Table I. Total mortality at 1 year is not as yet signifi-

TABLE I

Results After Surgery

Followup

(mean Mortality (%)

Group months) Operative Late Totai

I 14.6 10.5 1.5 11.9 II 28.0 19.4 16.6 36.0

cantly less in group I than in group III, due to the im- pact of operative deaths, but is significantly greater in group II. Bypass graft surgery resulted in signifl- cantly decreased late mortality and improved functional classification (3.2 to 1.5 postoperatively) compared to insignificant improvement in groups II and III.

Potentiation of Contraction by Premature Activation in Patients with Normal and Abnormal Left Ventricular Function

RALPH SHABETAI, MD, FACC*: JOHN B. UTHER, MD; KIRK L. PETERSON, MD; JOHN ROSS, Jr., MD, FACC, San Diego, Cali- fornia

It has been reported that in myocardiopathic rats the Bowdich effect is absent. This suggests a defect in electromechanical coupling. Accordingly, the enhanced cardiac performance that occurs in the contraction im- mediately following premature ventricular depolariza- tion was studied in 10 patients with sinus rhythm and

highest value attained for the expression p dp/dt and

Vmax (using P and linear extrapolation). Normal beats were compared with beats having a short pre- ceding R-R interval (RRl) and long or normal R-R interval (RR2). Short RR1 was 436 -C 1’7 msec SEM for LVN and 458 + 48 msec for LVD. The percent increase in contractility indexes for beats with short RR1 are shown in Table I.

TABLE I

Percent Increase in Contractility Indexes

Index LVN LVD

Peak dp/dt 25 + 6 31A 4

34 zt 6

20+ 5

Vmax 39* 4 34zk 8

Contractility increased in all beats in all patients when a normal or long RR2 followed a short RRl. This increase did not differ statistically between LVN and LVD or between short RR1 caused by ES or occurring in normally conducted beats in AF.

It is concluded that a deficiency in electromechanical coupling was not uncovered in these patients with LVD. Our study also demonstrated an alteration in inotropic state, representing an expression of the force-frequency relation in patients with atria1 fibrillation.

Exercise Heart Rate and Blood Pressure in Electrocardiographic Stress Test Design

L. THOMAS SHEFFIELD, MD, FACC*; DAVID ROITMAN, MD, Birmingham, Alabama

We inquired whether the product of heart rate (HR) and systolic blood pressure (SBP) would permit a more precise definition of a “standard stress” than would the use of HR alone, measuring 223 tests on untrained pa- tients over age 30 years and free of factors known to equivocate the “ischemic S-T depression” response. There were 89 negative and 134 positive responses. Mean age of the subjects was 49 years (range 30-72). In each test exercise was terminated upon evidence of exercise intolerance, S-T segment depression, or soon after reaching target heart rate. Peak exercise HR and HR x SBP were examined in relation to age and elec- trocardiographic response.

Patients with negative responses reached not less than 10 beats/min of target HR in 98% of tests. In patients with ischemic responses mean HR was much lower than in those with negative responses, but the upper ranges of HR were the same in both groups. A

VOLUME 29, FEBRUARY 1972 291

ABSTRACTS

linear regression in the age range 40 to 68 years was evident (HR = 184 - 0.79 [age 40 years] ), below which occurred 128 positive HR responses (98yG). HR x SBP provided a wider dispersion of data than HR alone. A level was found (35 mm Hg/min) which would include 95% of those with positive responses, but <75c/, of those with negative responses reached even 30 mm Hg/min, so aiming for such a product would be point- less. In summary, the merit of HR x SBP for predict- ing onset of ischemia in the individual patient does not appear to hold for general application as a stress end- point in exercise testing, but 35 mm Hg/min may be used as an effective end-point for the occasional subject who achieves this level. However, there is an age re- gression of exercise HR that includes 98’;, of those with positive responses, the attainment of which is therefore a strongly negative result if no evidence of ischemia is manifested.

Noninvasive Determination of Infarct Size 5 Hours After Coronary Occlusion in the Conscious Dog

WILLIAM E. SHELL, MD*; BURTON E. SOBEL, MD, FACC; JAMES W. COVELL, MD; JOHN F. LAVELLE, MS, La Jolla, California

This study was designed to predict infarct size (IS) within 5 hours in the conscious dog subjected to coro- nary occlusion and to measure changes in IS following isoproterenol administration. We have previously shown that IS is reflected by the pattern of serial serum creatine phosphokinase (CPK) changes during the 24 hours following occlusion. In the present study, serum CPK changes were measured in 21 conscious dogs subjected to coronary occlusion. Results were fit to a log normal function by least squares approxima- tion. When the function was fit with values obtained during only the first 5 hours following occlusion, the derived curve predicted IS accurately (IS,,). Correla- tion coefficients between fit curves and actual serial 24 hour values in animals with occlusion alone were 0.94 2 0.03 (mean % SE), no. = 10. Differences between IS,, calculated from CPK changes during only the first 300 minutes and infarct size (range: 0.4 = 60 g) based on myocardial CPK analysis were small, 0.3 ? 2.4 g (mean t SE). In 11 additional dogs isoproterenol, 0.015 mg/kg subcutaneously, was administered at least 10 hours after coronary occlusion, In all, subsequent serum CPK values deviated from those predicted by the log normal function. Hence, IS calculated from 24 hour serum CPK changes exceeded IS,, by an average of 219’: (P <O.Ol). Extension of infarction produced by isoproterenol was corroborated by postmortem myo- cardial CPK analysis. Thus, anticipated serum CPK changes, IS and quantification of extension can be de- termined promptly and noninvasively by appropriate analysis of early serum CPK elevations in individual conscious dogs.

The Effect of Variation in Arterial Oxygen Tension on Fetal Circulation

BIJAN SIASSI, MD*; IRWIN TESSLER, MD; PAUL Y. K. WU, MD: HOUCHANG MODANLOU, MD; RAYMOND LI. MD, Los Angeles, California

The cardiovascular effect of changes in fetal arterial oxygen tension (PO,) was studied in 7 closed-chest

fetal lambs maintained in normal physiologic condition connected to an extracorporeal circuit functioning as an “artificial placenta.” While fetal rectal temperature was maintained at 3’7 to 39C, umbilical arterial (UA) pH 7.30 to 7.40, UA pCOZ 35 to 45 mm Hg and placental flow (extracorporeal) 110 to 130 ml/kg per min, fetal circulation was investigated by dye-dilution technique at UA p0, of 20 to 30 mm Hg (fetal normoxia) and 35 to 45 mm Hg (fetal hyperoxia). Dye was injected suc- cessively into superior vena cava (SVC), inferior vena cava, right ventricle (RV) and left ventricle (LV) while being sampled from the ascending and descend- ing aorta (DA).

During fetal normoxia, effective cardiac output was 305 2 28 ml/kg per min, LV output 153 & 25 ml/kg per min, pulmonary circulation time 5.8 % 0.8 seconds and a large right to left (R-L) ductal shunt was pres- ent in each instance. SVC flow was directed to the right ventricle and through the ductus arteriosus into the descending aorta. During fetal hyperoxia LV output in- creased markedly to 269 * 26 ml/kg per min, approxi- mating the effective cardiac output, pulmonary circula- tion time decreased to 2.1 -C 0.3 seconds, whereas R-L ductal flow disappeared in 5 and markedly decreased in 2 instances. From this study it appears that, in fetal lambs, hyperoxia beyond an UA p0, of 35 mm Hg leads to closure of ductus arteriosus and marked decrease in pulmonary vascular resistance while allowing a sizable shunt through the foramen ovale.

A Method of Quantifying the Need for Surgical Therapy in Clinical Myocardial Infarction Shock

JOHN H. SIEGEL, MD*; EDWARD J. FARRELL, ES; ISAAC LEWIN, MD; DAVID BREGMAN, MD, NewYork, NewYork

Determining the need for mechanical support or acute revascularization, or both, before irreversible myo- cardial damage occurs presents a major problem in the treatment of myocardial infarction (MI) shock. By de- scribing the magnitude and the shape of the central indicator-dilution curve using a mathematic model which quantifies the dye curve by 4 independent in- dexes, flow, and the delay, dispersion (non-mixing) and mixing mean transit times, more than 1,000 indicator curves from 197 patients with septic, nonseptic, and myocardial infarction shock, and from preoperative control patients without shock were analyzed. Mixing time (t,,,) reflects changes in the durational aspects of myocardial contractility. Dispersive time (t,,) ordi- narily reflects transit across pulmonary small vessels, but some patients with MI have a large cardiac non- mixing volume which appears related to the size of the infarct and its penumbra of isehemic myocardium. The persistence of a t,,, >7.5 seconds and presence of a cardiac nonmixing volume with a t,, of >7.5 are signs of medically refractory MI shock requiring circulatory support. Of 28 patients with MI shock none survived in whom both t,, and t,,, values were not decreased be- low 7.5 seconds by medical or mechanical support therapy. Intraaortic double balloon counterpulsation was used in 9 MI patients. The 3 patients resuscitated from acute MI shock all had reductions in t,, and t,,,. The 6 nonsurviving patients did not. With these in- dexes it appears possible to quantify the effectiveness

292 The American Journal of CARDIOLOGY