TUESDAY AFTERNOON, MAY 1, 1979

2:00 P.M. Scientific Session - Ballroom

23. A Comparison of Crystalloid and Blood Potassium Cardioplegia During Prolonged Hypothermic Aortic Occlusion

SHINICHI TAKAMOTO*, FREDERICK H. LEVINE*,

N. SCOTT ADZICK*, PAUL J. LARAIA *, JOHN T. FALLON*,

W. GERALD AUSTEN and MORTIMER J. BUCKLEY,

Boston, Massachusetts

Blood cardioplegia has recently been advocated as a superior method of myocardial protection, but comparison to an asanguinous crystalloid cardioplegic solution has not been presented. This study was undertaken to compare the protective effect of blood (BCP) and crystalloid (KCP) potassium cardioplegic solutions during 2 hours of hypothermic (22°C) aortic occlusion and 45 minutes of reperfusion (R). Twelve dogs were placed on cardiopulmonary bypass. In six dogs the aortic root was perfused with BCP (Hct 35%) and in the other six dogs KCP was used. Both perfusates contained 25 meg/L KCI buffered to pH 7.4. Change in ventricular function was defined as the arithmetic difference in center of mass between pre and post arrest Sarnoff curves and expressed as percent recovery of function. Regional myocardial flow was measured with microspheres and metabolism monitored by lactate and oxygen utilization. Ventricular biopsies were serially obtained for myocardial water, electron microscopy, and ATP, CP and Ca++. The KCP group recovered 75% of function while recovery in the BCP group was 65%. Endo/epicardial flow ratio was increased immediately after R in both groups but return to baseline was prolonged in the BCP group (1.36 vs 1.04 at 10 min R (p<.05) indicating less adequate myocardial protection. Oxygen consumption (BCP-5.6 vs KCP-5.6 ml/100g/min) was lactate extraction (BCP-0.042 vs KCP-0.049 mM/min) were simUar in both groups after R. Small but similar increases in myocardial water (BCP-1.9 vs KCP-2.1%) were noted and ATP, CP and Ca⁺⁺ levels were well preserved in both groups. Electron microscopy demonstrated similar minor endothelial and myocytic changes.

BCP offers no advantage over a similar KCP solution. Though protection is adequate in both groups, ventricular function and blood flow distribution are better preserved with an asanguinous perfusate. The oxygenated environment of BCP may preclude the rapid arrest necessary for optimal myocardial protection.

*By invitation

24. The Importance of Preoperative Myocardial Nutrition in Human Cardiac Preservation

DAVID M. LOLLEY*, JEFFERSON F. RAY, III,

WILLIAM O. MYERS, RICHARD D. SAUTTER and

DUANE A. TEWKSBURY*, Marshfield, Wisconsin

Glycogen is an important indicator of cardiac nutrition acting as an energy source during stress with enhanced levels increasing cardiac tolerance to acute ischemia. This prospective study was designed to see if improved myocardial nutrition results in significant preservation of the human heart during cardiac surgery. Coronary artery surgery patients (n=117) were divided into four groups of similar size. Group I had low cardiac glycogen and no cardioplegia, group II had low cardiac glycogen and KC1 cardioplegia, group III had high cardiac glycogen and no cardioplegia, and group IV had high cardiac glycogen and KC1 cardioplegia. All cases were done with systemic and topical hypothermia, intermittent cross-clamping, and moderate hemodilution. Enhanced cardiac glycogen was achieved with overnight glucose with or without fat loading diet.

The protective effect of elevated glycogen levels resulted in significantly lower rates of serious atrial and ventricular arrhythmias and vasopressor need whether the patients received chemical cardioplegia or not. The favorable results in group III indicate that preoperative anaerobic substrate enhancement alone can result in myocardial protection which is equivalent to that achieved by chemical cardioplegia and is independent of its components. The beneficial effects of cardioplegia and enhanced myocardial glycogen (group IV) can be additive to effect the best clinical cardiac performance. Enhancing the nutritional status of the heart before subjecting it to the stress of acute ischemia and cardiopulmonary bypass can be a beneficial adjunct to most techniques of myocardial preservation.

*By invitation

25. Reversal of Ischemic Damage with Secondary Blood Cardioplegia

HAROLD LAZAR *, ANDREW MANGANARO*,

ROBERT FOGLIA *, HEINZ BECKER * JAMES V. MALONEY, JR

and GERALD D. BUCKBERG, Los Angeles, California

After severe ischemic injury, it is usually necessary to prolong bypass to enhance recovery. This study tests the hypothesis that the best reversal of ischemic damage can be achieved by briefly rearresting the postischemic heart with a continuous infusion of a blood cardioplegic solution (secondary cardioplegia) during the recovery phase occurring while bypass must be prolonged. This hypothesis is based on the finding that ischemic damage limits the heart's ability to use oxygen so that prolongation of bypass alone does not lower oxygen demands sufficiently to allow complete cellular recovery.

METHODS: Fifteen dogs underwent 45 minutes of normothermic ischemic arrest. Fifteen minutes after unclamping, no heart could support the systemic circulation. In all dogs, we reduced cardiac 0₂ demands by immediately reinstituting total bypass for 30 more minutes. In 10 of these dogs, we reclamped the aorta for 5 minutes and lowered 0₂ demands further by continuously infusing a 37°C blood cardioplegic solution (K⁺ 30mEq/L, pH 7.6, CA⁺⁺ ImEq/L) at 50-75 ml/min. In all studies, coronary blood flow (microspheres), metabolism (LV0₂ uptake), water content (wet/dry weight), LV compliance (intraventricular balloon), and LV performance (Starling curves) were measured during control and at 15 and 45 minutes after unclamping.

RESULTS: Dogs treated by prolonging bypass alone for 45 minutes showed progressive but limited improvement in ventricular function, water content, compliance, and the ability to use oxygen. Hearts treated with secondary blood cardioplegia during prolonged bypass, however, showed better recovery of compliance (85 vs 55%*), a higher stroke work index (0.72 vs 0.52 g-m/kg*), and more ability to augment 0₂ uptake (85 vs 45%*) when demands were increased by making the heart work.

CONCLUSION: Rearresting the heart with a brief, continuous infusion of a blood cardioplegic solution results in more complete reversal of ischemic damage than possible by prolongation of bypass alone. We believe the increased recovery with secondary cardioplegia results from diversion of delivered oxygen towards reparative processes rather than by expending needless electromechanical work while bypass must be prolonged.

p<.025 cardioplegia vs prolonged bypass at 45 minutes

*By invitation

26. Protection of Myocardial Function Not Enhanced by High Concentrations of Potassium During Cardioplegic Arrest

R. J. ELLIS*, D. MANGANO*, D. VANDYKE*, and

PAUL A. EBERT, San Francisco, California

The effect of high (20 mEq/L) versus physiologic (5 mEq/L) concentrations of potassium in hypothermic cardioplegic arrest was compared in twenty patients undergoing myocardial revascularization. Ten patients received high potassium solution and ten received the low K solution. The patients were selected randomly and were comparable in all important respects. All distal anastomoses were performed under one continuous cardioplegic arrest (40-60 min) induced by a single infusion of 800 ml of cardioplegic solution. Myocardial function was assessed by intraoperative measurement of ejection fraction (EF) using a precordial scintillation probe. The probe enabled computation of ejection fraction by recording the passage of an injection of Teh⁹⁹ albumin through the central circulation. Simultaneous cardiac output determinations were made by thermal dilution and pulmonary capillary wedge pressures (PCW) at various loading conditions before and 30 minutes after the termination of cardiopulmonary bypass. LV compliance (PCW vs EDV), and ventricular function (SWI vs EDV) were computed using the measurement of end diastolic volume (EDV). Myocardial oxygen consumption was estimated using the product of heart rate times systolic blood pressure (HR x SBP).

RESULTS:

CONCLUSION:

The addition of high concentrations of potassium to hypothermic perfusates did not enhance protection of the myocardium during cardioplegic arrest. Cardiac performance was the same whether a high or physiologic potassium concentration was used. We conclude that a high concentration of potassium in cardioplegic solutions is of no demonstrable value

INTERMISSION - VISIT EXHIBITS

*By invitation

27. Preservation of ATP, infrastructure, and Ventricular Function Following Aortic Crossclamping and Reperfu-sion - Clinical Use of K⁺ Blood Cardioplegia

JOSEPH N. CUNNINGHAM, JR., PETER X. ADAMS*,

EDMOND A. KNOPP*, F. GREGORY BAUMANN*, and

FRANK C. SPENCER, New York, New York

Multidose blood cardioplegia (K⁺ 30 mEq/L, pH 7.4, normal Ca++) in combination with profound myocardial hypothermia (<20°C) was studied in 24 patients undergoing cardiac surgery. Serial myocardial biopsies were obtained to assess the preservation of myocardial ATP and ultrastructure during crossclamping and after reperfusion. Cardiac output was measured serially before and after bypass.

Several technical details were found of crucial importance. These included: monitoring myocardial temperature and avoiding rewarming, topical hypothermia (endocardial and epicardial), volume and frequency of cold blood injection, and monitoring of injectate pressure.

Patients could be divided into 2 groups: Grp. I (17 pts.) had optimal myocardial protection (multidose reinjections, maintenance of myocardial temperature <20°C, and absence of EKG activity during cross-clamping). Grp. II (7 pts.) had some return of EKG activity and rise in myocardial temperature (>25°C) before unclamping because of errors in technique.

The finding that ATP actually increased (53%) during crossclamping and returned to normal following reperfusion indicates excellent myocardial protection. This is supported by electron microscopic findings (no irreversible changes) and the absence of low cardiac output. In contrast, the importance of technical details, especially the degree of hypothermia, is shown by the ATP decrease in Grp. II, frequently followed by poor cardiac function and irreversible ultrastructural changes. These data indicate that with proper technique, cold blood K⁺ cardioplegia combined with topical cooling is distinctly superior to other methods of myocardial protection.

*I vs. II-p>.05 **p<05

*By invitation

28. Changing Patterns in Pacemaker Patient Care, 1963-78

JOSEPH W. RUBIN*, ROBERT G. ELLISON, H. VICTOR MOORE*,

and GANESH PAI*, Augusta, Georgia

Transtelephone surveillance (TTS) of pacemaker patients, with electrocardiograms recorded weekly or monthly, is often initially accompanied by an observed increase in pacemaker system malfunction. This apparent increase probably more nearly reflects the true incidence of pacemaker system malfunction. Industry claims of pacemaker reliability are misleading because of incomplete retrieval of out-of-use generators. A review of 16 years of pacemaker experience at the Medical College of Georgia was analyzed to determine survival, complications, and effectiveness of follow-up techniques in a 300-mile radius area. 461 consecutive patients have undergone 687 subsequent operations for battery and/or lead replacement and for complications of the pacemaker system (M 2.5 operations/patient). 891 generators (794 Hg-Zn, 93 lithium, 4 plutonium-238) were used. Of 253 patients now alive, 152 are followed by our TTS system, 66 are seen by personal physicians and infrequently in pacemaker clinics, 31 have moved or transferred care, and 4 pacemaker systems have been removed. In 2 years, TTS has detected 60 complications of pacing systems (asymptomatic in 39) which, if undetected, could progress to pacing failure; 38 patients required re-operation. Local physicians were notified of arrhythmias, congestive failure, etc. in 46 patients. Generator exhaustion accounted for only 20% of pacemaker malfunction in the TTS group; lead and sensing problems (53%), component failure (15%), and wound problems (12%) also complicated pacemaker performance. Average life of generators followed by TTS to battery exhaustion was 43 mo., while overall Hg-Zn generator life averaged only 25 mo. During the first 2 years of TTS, 13% (22 of 174) of the TTS group died, while 38% (41 of 107) of the non-TTS group died. TTS is inexpensively available and greatly improves patient safety.

4:00 P.M. Executive Session (limited to Active and Senior Members) -Ballroom

*By invitation

TUESDAY EVENING, MAY 1, 1979

7:00 P.M. President's Reception - Constitution Ballroom

8:00 P.M. President's Dinner and Dance - Ballroom