- Email: [email protected]
MONITORING OF CORONARY ARTERY PERFUSION
M O N I T O R I N G OF CORONARY ARTERY PERFUSION F. B. Clarke, M.B., B.S., F.F.A.R.A.C.S.,*
Camperdown,
Sydney,
Australia
T
HE maintenance of a viable myocardium during aortic valve surgery has been a problem since Swan 1 and Lewis2 performed the first aortic valvotomy under direct vision. Hypothermia has been used extensively, with and without coronary artery perfusion. At present, coronary artery perfusion with indi vidual pumps is widely practiced. F a r too commonly a myocardium did not take over the circulation follow ing a technically successful operation. Many surgeons have accepted ventricular fibrillation during coronary perfusion as a satisfactory physiological state. We have found that the adequacy of the coronary perfusion can be monitored by means of the electrocardiograph and the surgeon can be warned of the changes that might lead to myocardial damage if uncorrected. By adjusting the perfu sion during the operation, survival of the myocardium is ensured. METHOD
The sheep's heart has been used to perfect a coronary perfusion technique for aortic valve surgery. We were interested in discovering the optimum perfusate, its temperature, a safe perfusion pressure, and an adequate flow rate. The quality of the cardiac contraction at the end of the experiment, as indicated by left atrial pressures and electrocardiograph records, was used as a guide to a good perfusion. The perfusates used were autogenous and heterogenous sheep's blood, both nondiluted and diluted, one part in four with 10 per cent Rheomacrodex. Perfusions were carried out at a variety of temperatures, ranging from 10° to 35° C. The perfusion pressure, flow rate, arterial and venous oxygen difference, pC0 2 , pH, and bicarbonate levels were measured. The p C 0 2 was varied with the temperature to keep the corrected p H at 7.4. RESULTS
Experimentally, a turgid hemorrhagic myocardium commonly occurred. Four conditions readily produced this pathologic condition. These were a perReceived for publication Dec. 21, 1964. •Staff Anesthetists: Royal Prince Alfred Hospital, Camperdown, Sydney, N.S.W., Aus
tralia.
931
932
CLARKE
J. Thoracic and Cardiovas. Surg.
CORONARY PERFUSION 30 MIN.
CORONARY PERFUSION OFF 2 MIN.
—K—
AORTA RELEASED 2 MIN.
OFF BYPASS
OFF BYPASS 2 0 MIN.
-LLLLU -L-LLLL
Fig. 1.—Electrocardiographic changes in Lead I during coronary artery perfusion.
^—U-l
BEFORE BYPASS BEFORE BYPASS
•YY-
JUX
TOTAL BYPASS 10 MIN. LEFT CORONARY 1 MIN. BOTH CORONARIES 2 MIN.
.f"*-^
BOTH CORONARIES 1 0 MIN,
Fig. 2.—Electrocardiographic changes in Lead I during coronary artery perfusion.
Vol.49, No. 6
MONITORING OP CORONAEY AKTERY PEEFUSION
933
June, 1965
fusion pressure over 100 mm. Hg, heterogenous blood, hypothermia, and ven tricular fibrillation. The most important factor was the perfusion px-essure. If this was main tained over 100 mm. Hg in the sheep for more than a few minutes, an irre versible pathological state ensued. This was particularly observed when the ventricles were fibrillating. It was noticed that the fibrillating ventricles in creased in weight by 50 per cent when perfused for 1 hour at 35° C. There was very little increase in weight following perfusion with normal contraction. Satisfactory cannulation and perfusion of the left coronary artery is fre quently difficult because of the early origin of the interventricular branch. The
BOTH C0R0NARIES 5 MIN.
AAAAA
BOTH C0R0NARIES 20 MIN.
AFTER BYPASS
/
4rJ[/4o 4^v~v*
Fig. 3.Electrocardiographs changes in Lead I during poor coronary artery perfusion, due to diseased coronary ostia,
BEFORE BYPASS
_
I
LEFT CORONARY 2 MIN.
BOTH CORONARIES 2 0 MIN.
-A
T\»
AORTA RELEASED h MIN.
Fig. 4.—Electrocardiographic changes in Lead I during poor coronary artery perfusion, due to diseased coronary ostia.
CLARKE
934
J. Thoracic and Cardiovas. Surg.
BEFORE BYPASS BOTH CORONARIES 9 MIN. BOTH CORONARIES 12 MIN.
-L^J-
BOTH CORONARIES 23 MIN. BOTH CORONARIES UO MIN. AORTA RELEASED OFF BYPASS
Fig. 5.—Electrocardiographs changes in Lead I during poor coronary artery perfusion.
length of the left coronary artery in man averages 8 mm. before a major branch. It is difficult to insert a cannula without occluding a branch and this is com monly the interventricular artery. I t has been our experience that ventricular fibrillation rapidly ensues if the perfusion is not satisfactory at 35° C , and we think that a low even flow through all branches is better than a higher flow along one coronary vessel. There is sufficient electrical potential generated by the p 0 2 and pH gradients between the well-perfused and poorly-perfused areas to cause ventricular fibril lation. 3 I t is desirable that both coronary arteries be perfused if technically possible, for the right one usually supplies a large part of the interventricular septum, and, in some cases, coronary angiography has been helpful in the plan ning of procedures. Following animal experimentation, a technique for clinical coronary per fusion was developed with the use of freshly heparinized blood, diluted by 30 per cent with normal saline and 5 per cent dextrose and albumen in equal pro portions at 32° C. By means of this method it has been possible to maintain the normal heartbeat and to monitor the adequacy of the coronary perfusion from the electrocardiogram. In most instances of inadequate perfusion, suf ficient warning has been given to enable the surgeon to re-adjust the cannulas before the onset of ventricular fibrillation. In view of the experimental demon stration of pathological changes in the myocardium, it is considered that the perfusion pressure should not be allowed to remain over 140 mm. Hg and that
Vol. 49, No. 6 June, 1965
MONITORING OF CORONARY ARTERY PERFUSION
BEFORE
CORONARY PERFUSION AORTA
3LAMPED CLAMPED
k MIN.
935
-Jp-*lp-^lp-4~*--l—J^""TV "Y\/~~~T\/~
BOTH CORONARIES I 2 MIN. '"'f
t— f
L-^~ T
BOTH CORONARIES k MIN. BOTH CORONARIES 10 MIN.
^AAJI^A^MT^
BOTH CORONARIES 30 MIN.
CORONARY PERFUSION OFF 1 MIN.
4 -N "lr v Jr u lr4' N -lr %
VENTRICULAR FIBRILLATION
3V C.
AFTER DEFIBRILLATION 1 MIN.
AW^V
DEFIBRILLATION 6 MIN.
OFF BYPASS
4^4^-i N ^1 X T V *T V '
Fig. 6.—A and B, Electrocardiographic changes in Lead I during coronary artery perfusion, with ventricular fibrillation on release of the aortic clamp.
936
CLARKE
J. Thoracic and Cardiovas. Surg.
flow should be sacrificed rather than risk damage to the arteries or to the myo cardium. Figs. 1-6 demonstrate the electrocardiographic changes that can be used to judge the adequacy of the coronary perfusion. During the 2 to 4 minute period of myocardial anoxia after the aorta has been clamped and incised and until coronary perfusion is established, inversion of the T waves, ventricular ectopic beats, and S-T segment changes are common electrocardiographic signs of myo cardial anoxia. When perfusion has been established, the electrocardiogram has been observed to return to and remain normal until the cannulas are removed just prior to completion of the aortic sutures. Figs. 1 and 2 show the electrocardiographic changes that occur commonly with no apparent myocardial damage. Figs. 3, 4, and 5 show electrocardiographic changes that may occur with little myocardial impairment. These tracings were from cases in which cannulation and perfusion were imperfect because of coro nary artery disease. The continuance of ectopic beats or deterioration of S-T segment changes demands readjustment of the cannulas. Fig. 6 illustrates this point, and also demonstrates ventricular fibrillation after release of the aortic clamp. This has occurred in 8 per cent of the cases. I t is probably due to air or calcific em bolism. Fig. 6 shows S-T segment changes which persisted for many months after successful aortic valve surgery. SUMMARY
On the basis of experimental and clinical experience, evidence is presented to support the belief that coronary perfusion at 32° C. with the heart beating and monitored by the electrocardiograph and by individual pressure gauges to each coronary line is a safe technique for giving adequate protection to the myocardium during aortic valve surgery. I should like to thank Mr. R. Nicks, Mr. A. Grant, and Mr. B . Leekie for their help in preparing this article. REFERENCES 1. Swan, H., and Kortz, A. B . : Direct Vision Trans-aortic Approach to Aortic Valve During Hypothermia, Ann. Surg. 144: 205, 1956. 2. Lewis, F . J., Shumway, N . E., Niazi, S. A., and Benjamin, R. B . : Aortic Valvulotomy Under Direct Vision During Hypothermia, J . THORACIC SURG. 32: 481, 1956. 3. Leighninger, D. S.: A Laboratory and Clinical Evaluation of Operations for Coronary A r t e r y Disease, J . THORACIC SURG. 30: 397, 1955.
Camperdown,
Sydney,
Australia
T
HE maintenance of a viable myocardium during aortic valve surgery has been a problem since Swan 1 and Lewis2 performed the first aortic valvotomy under direct vision. Hypothermia has been used extensively, with and without coronary artery perfusion. At present, coronary artery perfusion with indi vidual pumps is widely practiced. F a r too commonly a myocardium did not take over the circulation follow ing a technically successful operation. Many surgeons have accepted ventricular fibrillation during coronary perfusion as a satisfactory physiological state. We have found that the adequacy of the coronary perfusion can be monitored by means of the electrocardiograph and the surgeon can be warned of the changes that might lead to myocardial damage if uncorrected. By adjusting the perfu sion during the operation, survival of the myocardium is ensured. METHOD
The sheep's heart has been used to perfect a coronary perfusion technique for aortic valve surgery. We were interested in discovering the optimum perfusate, its temperature, a safe perfusion pressure, and an adequate flow rate. The quality of the cardiac contraction at the end of the experiment, as indicated by left atrial pressures and electrocardiograph records, was used as a guide to a good perfusion. The perfusates used were autogenous and heterogenous sheep's blood, both nondiluted and diluted, one part in four with 10 per cent Rheomacrodex. Perfusions were carried out at a variety of temperatures, ranging from 10° to 35° C. The perfusion pressure, flow rate, arterial and venous oxygen difference, pC0 2 , pH, and bicarbonate levels were measured. The p C 0 2 was varied with the temperature to keep the corrected p H at 7.4. RESULTS
Experimentally, a turgid hemorrhagic myocardium commonly occurred. Four conditions readily produced this pathologic condition. These were a perReceived for publication Dec. 21, 1964. •Staff Anesthetists: Royal Prince Alfred Hospital, Camperdown, Sydney, N.S.W., Aus
tralia.
931
932
CLARKE
J. Thoracic and Cardiovas. Surg.
CORONARY PERFUSION 30 MIN.
CORONARY PERFUSION OFF 2 MIN.
—K—
AORTA RELEASED 2 MIN.
OFF BYPASS
OFF BYPASS 2 0 MIN.
-LLLLU -L-LLLL
Fig. 1.—Electrocardiographic changes in Lead I during coronary artery perfusion.
^—U-l
BEFORE BYPASS BEFORE BYPASS
•YY-
JUX
TOTAL BYPASS 10 MIN. LEFT CORONARY 1 MIN. BOTH CORONARIES 2 MIN.
.f"*-^
BOTH CORONARIES 1 0 MIN,
Fig. 2.—Electrocardiographic changes in Lead I during coronary artery perfusion.
Vol.49, No. 6
MONITORING OP CORONAEY AKTERY PEEFUSION
933
June, 1965
fusion pressure over 100 mm. Hg, heterogenous blood, hypothermia, and ven tricular fibrillation. The most important factor was the perfusion px-essure. If this was main tained over 100 mm. Hg in the sheep for more than a few minutes, an irre versible pathological state ensued. This was particularly observed when the ventricles were fibrillating. It was noticed that the fibrillating ventricles in creased in weight by 50 per cent when perfused for 1 hour at 35° C. There was very little increase in weight following perfusion with normal contraction. Satisfactory cannulation and perfusion of the left coronary artery is fre quently difficult because of the early origin of the interventricular branch. The
BOTH C0R0NARIES 5 MIN.
AAAAA
BOTH C0R0NARIES 20 MIN.
AFTER BYPASS
/
4rJ[/4o 4^v~v*
Fig. 3.Electrocardiographs changes in Lead I during poor coronary artery perfusion, due to diseased coronary ostia,
BEFORE BYPASS
_
I
LEFT CORONARY 2 MIN.
BOTH CORONARIES 2 0 MIN.
-A
T\»
AORTA RELEASED h MIN.
Fig. 4.—Electrocardiographic changes in Lead I during poor coronary artery perfusion, due to diseased coronary ostia.
CLARKE
934
J. Thoracic and Cardiovas. Surg.
BEFORE BYPASS BOTH CORONARIES 9 MIN. BOTH CORONARIES 12 MIN.
-L^J-
BOTH CORONARIES 23 MIN. BOTH CORONARIES UO MIN. AORTA RELEASED OFF BYPASS
Fig. 5.—Electrocardiographs changes in Lead I during poor coronary artery perfusion.
length of the left coronary artery in man averages 8 mm. before a major branch. It is difficult to insert a cannula without occluding a branch and this is com monly the interventricular artery. I t has been our experience that ventricular fibrillation rapidly ensues if the perfusion is not satisfactory at 35° C , and we think that a low even flow through all branches is better than a higher flow along one coronary vessel. There is sufficient electrical potential generated by the p 0 2 and pH gradients between the well-perfused and poorly-perfused areas to cause ventricular fibril lation. 3 I t is desirable that both coronary arteries be perfused if technically possible, for the right one usually supplies a large part of the interventricular septum, and, in some cases, coronary angiography has been helpful in the plan ning of procedures. Following animal experimentation, a technique for clinical coronary per fusion was developed with the use of freshly heparinized blood, diluted by 30 per cent with normal saline and 5 per cent dextrose and albumen in equal pro portions at 32° C. By means of this method it has been possible to maintain the normal heartbeat and to monitor the adequacy of the coronary perfusion from the electrocardiogram. In most instances of inadequate perfusion, suf ficient warning has been given to enable the surgeon to re-adjust the cannulas before the onset of ventricular fibrillation. In view of the experimental demon stration of pathological changes in the myocardium, it is considered that the perfusion pressure should not be allowed to remain over 140 mm. Hg and that
Vol. 49, No. 6 June, 1965
MONITORING OF CORONARY ARTERY PERFUSION
BEFORE
CORONARY PERFUSION AORTA
3LAMPED CLAMPED
k MIN.
935
-Jp-*lp-^lp-4~*--l—J^""TV "Y\/~~~T\/~
BOTH CORONARIES I 2 MIN. '"'f
t— f
L-^~ T
BOTH CORONARIES k MIN. BOTH CORONARIES 10 MIN.
^AAJI^A^MT^
BOTH CORONARIES 30 MIN.
CORONARY PERFUSION OFF 1 MIN.
4 -N "lr v Jr u lr4' N -lr %
VENTRICULAR FIBRILLATION
3V C.
AFTER DEFIBRILLATION 1 MIN.
AW^V
DEFIBRILLATION 6 MIN.
OFF BYPASS
4^4^-i N ^1 X T V *T V '
Fig. 6.—A and B, Electrocardiographic changes in Lead I during coronary artery perfusion, with ventricular fibrillation on release of the aortic clamp.
936
CLARKE
J. Thoracic and Cardiovas. Surg.
flow should be sacrificed rather than risk damage to the arteries or to the myo cardium. Figs. 1-6 demonstrate the electrocardiographic changes that can be used to judge the adequacy of the coronary perfusion. During the 2 to 4 minute period of myocardial anoxia after the aorta has been clamped and incised and until coronary perfusion is established, inversion of the T waves, ventricular ectopic beats, and S-T segment changes are common electrocardiographic signs of myo cardial anoxia. When perfusion has been established, the electrocardiogram has been observed to return to and remain normal until the cannulas are removed just prior to completion of the aortic sutures. Figs. 1 and 2 show the electrocardiographic changes that occur commonly with no apparent myocardial damage. Figs. 3, 4, and 5 show electrocardiographic changes that may occur with little myocardial impairment. These tracings were from cases in which cannulation and perfusion were imperfect because of coro nary artery disease. The continuance of ectopic beats or deterioration of S-T segment changes demands readjustment of the cannulas. Fig. 6 illustrates this point, and also demonstrates ventricular fibrillation after release of the aortic clamp. This has occurred in 8 per cent of the cases. I t is probably due to air or calcific em bolism. Fig. 6 shows S-T segment changes which persisted for many months after successful aortic valve surgery. SUMMARY
On the basis of experimental and clinical experience, evidence is presented to support the belief that coronary perfusion at 32° C. with the heart beating and monitored by the electrocardiograph and by individual pressure gauges to each coronary line is a safe technique for giving adequate protection to the myocardium during aortic valve surgery. I should like to thank Mr. R. Nicks, Mr. A. Grant, and Mr. B . Leekie for their help in preparing this article. REFERENCES 1. Swan, H., and Kortz, A. B . : Direct Vision Trans-aortic Approach to Aortic Valve During Hypothermia, Ann. Surg. 144: 205, 1956. 2. Lewis, F . J., Shumway, N . E., Niazi, S. A., and Benjamin, R. B . : Aortic Valvulotomy Under Direct Vision During Hypothermia, J . THORACIC SURG. 32: 481, 1956. 3. Leighninger, D. S.: A Laboratory and Clinical Evaluation of Operations for Coronary A r t e r y Disease, J . THORACIC SURG. 30: 397, 1955.