ABSTRACTS

USE AND LIMITATIONS OF VENTRICULAR PREMATURE BEATS AS PROGNOSTIC INDICATORS OF THE POSTHOSPITAL COURSE OF MYO- CARDIAL INFARCTION Arthur J. Moss, MD, FACC; John DeCamilla, BA; Henry Davis, PhD; Leonard Bayer, MA; Sidney Goldstein, MD, FACC, Uni- versity of Rochester, Rochester, New York.

The clinical significance of ventricular premature beats (VPB) in the posthospital phase of myocardial infarction (MI) was studied in 273 pts ~65 years of age who were fol- lowed for one year after an index MI. Six VPB character- istics were identified on predischarge (PD) and 4-month posthospital (PH) six-hour ECG tape recordings. The pro- portion of pts having each of the following VPB parameters increased significantly (p<O.Ol) over time (PD to PH): any (48 to 63%); >20/hr (7 to 17%); multiform (8 to 18%); bigeminy (4 to 20%); and pairs (3 to 12%). Analysis by log linear modeling indicated that the increase in VPBs over 4 months was not related to the change in use of an- tiarrhythmic agents, beta blockers, or digitalis. In 179 pts with VPBs at PD and/or PH, VPB frequency s20/hr at PD was associated (~~0.05) with 4-month PH VPB fTequency > 20/hr, bigeminy, and prematurity (RR'/QT ~1.00). VPBs, 20/hr at discharge were associated with an increased (p-c 0.05) 4-month PH cardiac mortality. However, the change in VPBs from PD to PH and the specific VPB characteristics at 4 months were not associated with an increased cardiac mortality in the 5-12 month follow-up. Conclusions: 1) VPBs increase in frequency and complexity during the ini- tial 4-month PH interval; 2) VPBs >2D/hr at PD identify pts with more complex VPB patterns-4 months later; 3) VPB frequency ,20/hr is a useful prognostic indicator of the initial 4-month PH course, but thereafter VPBs lose their prognostic specificity.

FREQUENCY AND SIGNIFICANCE OF LEFT CORONARY ARTERIAL DOMINANCE IN ISOLATED AORTIC STENOSIS Edward Murphy, MD; Josef Rosch, MD; Robert Lawson, MD; Albert Starr, MD, FACC; Shahbudin Rahimtoola, MD, FACC, University of Oregon Health Sciences Center, Portland, OR

Myocardial infarction during aortic valve replacement (AVR) can result from obstruction of a branch of the left main coronary artery (LMCA) by the perfusion cannula. Pa- tients (pts) with left dominant (LD) coronary artery (CA) system may be at greater risk. To assess the frequency and significance of LD, CA systems, we have evaluated the coronary angiograms of 75 pts with isolated aortic sten- osis (AS) aged '34 yrs and of a control group of 150 pts.

Of the AS pts, 19 (25%) had left dominant (LD), 9 (12%) balanced, and 47 (63%) had right dominant (RD) CA system. Of the control pts, 14 (9%) had LD, 18 balanced (12%) and 118 (79%) were RD. The increased (25%) incidence of LD in AS was significant (p c.005). In AS pts, the LMCA was shorter (p <.Ol) in those with LD (6.251.3 mm, mean + SE) than in those with RD (9.950.7).

_

Sixty-nine pts with AS underwent aortic valve replace- ment. The incidence of perioperative myocardial infarc- tion in LD was 26.7% (4 of 15) and in RD or balanced was 7.4% (4 of 54).

In conclusion, in AS there is an increased incidence of LD, CA systems, which suggests that these may be as- sociated congenital defects. In such pts, the length of the LMCA is shorter than in those with RD. There is an increased risk of perioperative myocardial infarction in AS pts with LDCA. Preop information about the CA anatomy may be helpful in planning use of coronary perfusion and of other myocardial preservation techniques during surg- ery in order that the incidence of myocardial infarction may be reduced.

IMPAIRED CALCIUM METABOLISM IN MITOCHONDRIA ISOLATED FROM ISCHEMIC AND REPERFUSED MYOCARDIUM - Marvin L. Murphy, MD, FACC; Chun-Fu Peng, Ph.D.; James J. Kane, MD; Karl D. Straub, MD; VA Hosp - Univ of Ark, Little Rock, Ark. Previous studies have demonstrated impaired mitochondrial function in acutely ischemic myocardium which is not im- proved by two hours of reperfusion. The defect appears to be a block in electron transport, thus implying that all energetic mitochondrial function is impaired. This study determines the effect of ischemia and reperfusion on energy-linked Ca" uptake by myocardial mitochondria. The left anterior descending coronary artery was occluded in 14 mature pigs for two hours. In 7 animals the ligature was released and the ischemic zone reperfused for 2 addi- tional hours. After sacrifice, mitochondrial function was measured in normal and reperfused or ischemic areas of the left ventricle, using a polarographic method. Mitochon- dria were prepared without EDTA by standard procedures and Ca* uptake measured by 4SCa* isotope tracer. Respira- tion linked Ca* uptake after two minutes using either glutamate, malate or succinate as substrates for normal, ischemic, and reperfused mitochondria is shown (Ca* up- take in n moleslmg protein): Substrate Normal Ischemic Reperfused

Glutamate 66 + 9 16+ 4 10 + 7 Malate 69 ? 11 28 + 12 9+5 Succinate 61 + 8 24 7 12 7T3

Ca" uptake in the presence or phosphate also was markedly impaired in ischemic and reperfused mechondria. Further more, in the presence of exogenous Ca phosphorylation of ADP by ischemic and reperfused mitochondria was totally inhibited. We conclude that: 1) Uptake of Ca* by mito- chondria derived from ischemic myocardium is markedly im- paired with or without phosphate. 2) Reperfusion may ac- centuate this impairment. 3) The presence of exogenous Ca* inhibits the ability of ischemic or reperfused mito- chondria to phosphorylate ADP.

BLOOD PRESSURE AND SYMPATHETIC NERVE ACTIVITY IN BACK- BRED NORMOTENSIVE RATS DERIVED FROM SPONTANEOUSLY HYPER- TENSIVE RATS. William R. Murphy, M.S., William V. Judy, Ph.D., August M. Watanabe, M.D., F.A.C.C., H.R. Besch, Jr., Ph.D. and Pao-Lo Yu, Ph.D., Departments of Physiology & Pharmacology, Indiana University School of Medicine, Indianapolis, Indiana 46202.

A major disadvantage of studying the Okamoto spontaneous- ly hypertensive rat (SHR) is the lack of suitable con- trols. By a series of back-breedings, we have recently been able to eliminate hypertension in rats genetically derived from SHR. These animals should be ideal con- trols for the hypertensive animals. The purpose of this study was to quantitate sympathetic nerve activity (SNA) and correlate these measurements with mean blood pressure (MBP) in back-bred normotensive and hyper- tensive SHR. All studies were done in 4-5 months old animals. Measurement of MBP and SNA in the animals revealed the following:

Back-bred SHR SHR Wistars

MBP (mm Hg) 162.4 * 11.7 106.7 * 4.3 118.6 l 7.2 SNA (uV) 59.6 * 7.9 16.7 * 4.6 18.7 * 7.0

Baroreceptor regulation of blood pressure was similar in back-bred SHR and Wistars but attenuated in SHR. These results suqqest that 1) elimination of hvoertension bv back-breeding is associated with a reduction in SNA; 2) differences in SNA between SHR and Wistars do not merely reflect genetic differences and 3) the elevated SNA in SHR may be causally related to the hypertension.

158 January 1978 The American Journal of CARDIOLOGY Volume 37