An improved method of topical cardiac hypothermia

J

THoRAc CARDIOVASC SVRG

82:878-882, 1981

An improved method of topical cardiac hypothermia Current methods of myocardial protection usually employ cardioplegic arrest together with topical hypothermia by pericardiallavage. Pericardiallavage is inconvenient. inconsistent. and noisy; it wastes blood; it cannot cool the right ventricle effectively. We use a new myocardial protection jacket to cool the heart during operations other than simple coronary bypass procedures. Myocardial temperatures are maintained at 7° to 14° C indefinitely without reinfusion of cardioplegia solution. The jacket is a more convenient and much more effective method of obtaining profound topical hypothermia.

Lawrence I. Bonchek, M.D., and Gordon N. Olinger, M.D., Milwaukee. Wis.

CardiOPlegiC arrest has become the most common method of intraoperative preservation of the myocardium, and laboratory and clinical investigations have repeatedly demonstrated that hypothermia is the essential component of the method. I, 2 Ellis and co-workers'' found that the myocardial protection provided by intracoronary injection of a cold isotonic electrolyte solution was not enhanced by the addition of high concentrations of potassium (20 mEq/L). Because the heart rewarms rapidly after single intracoronary injections of cold cardioplegic solutions," multiple injections are usually used, supplemented with topical hypothermia. Even when the aorta is not open and the aortic valve is competent, multiple infusions of cold cardioplegic solutions are tedious; they enhance the likelihood of intracoronary injections of air; they may cause damage to the endothelium of coronary arteries and saphenous vein grafts; and they can cause myocardial edema or other cellular injuries that are still poorly defined. Blood cardioplegic solutions are usually not as cold as crystalloid solutions.v ? and topical hypothermia then may be even more important. Unfortunately, conventional topical hypothermia has many disadvantages. Intermittent pericardiallavage has

From the Medical College of Wisconsin, Milwaukee, Wis. Received for publication March 10, 1981. Accepted for publication April 27, 198I. Address for reprints: Lawrence I. Bonchek, M.D., Professor and Chairman, Department of Cardiothoracic Surgery, The Medical College of Wisconsin, 8700 W. Wisconsin Ave., Milwaukee, Wis. 53226.

878

little effect on myocardial temperature" and even continuous lavage is not very effective in large hearts. 9 Continuous lavage is expensive and awkward, since cold bottles of solution must be changed frequently; it is inconsistent, since cold bottles of fluid begin to warm when they are brought into the operating room; it requires frequent attention and adjustment; the noise of the continuous pericardial sump suction is distracting at the very least and quite annoying at worst; blood that enters the pericardial space is wasted, since it is discarded with the lavage fluid; the posterior wall of the left ventricle may not be cooled well because it rests on the posterior pericardium; and the anterior wall of the heart is hardly ever beneath the level of cold solution. For mitral valve operations in particular, inadequate protection of the right ventricle may be especially harmful. 10 We therefore developed a device that permits continuous circulation of cold solution around the entire surface of the heart in a closed system. This method of topical hypothermia eliminates the disadvantages mentioned earlier and provides more effective and uniform topical hypothermia than does the conventional system of lavage. The device was not developed for use in routine coronary bypass operations, since any method of topical hypothermia is difficult to apply and much less effective in such cases; it is used for operations on the heart valves or ascending aorta, whether these are isolated or combined with coronary bypass. In children, smaller jackets might be useful for many operations to correct congenital anomalies, since most such operations are now carried out through incisions in the atria or the great vessels.

0022-5223/81/120878+05$00.50/0 © 1981 The C. V. Mosby Co.

Volume 82 Number 6 December, 1981

Topical cardiac hypothermia

879

Fig. 1. The myocardial protection jacket in the open position. The path of fluid through the jacket is predetermined by the sealing process. In the size shown, the short sides are each 9.5 em and the long sides are 33 and 28 ern. The jacket is 7 mm thick when fluid is circulating.

Myocardial protection jacket The device (Fig . I) is a flexible plastic jacket that encloses a continuous path for fluid. When the jacket is placed around the heart and is secured by the Velcro fastener, the trapezoidal shape of the jacket conforms to the conical shape of the heart and completely encloses both ventricles from the atrioventricular groove to the apex (Fig. 2), but does not interfere with access to the atria or to the aorta. Small ('1.1 inch diameter) inlet and outlet tubes lie unobtrusively at the lowest portion of the sternotomy incision. Cold electrolyte solution circulates through the jacket in a closed system of tubing that includes a coil immersed in saline slush, and another section that passes through a roller pump head. When the system is primed, air is evacuated through a bubble trap. Since the system is closed, high (bursting) pressures would not develop if the circuit became obstructed, because the pump head would not receive fluid. The serpiginous path of the fluid through the jacket is predetermined so that cold fluid cannot shunt around areas compressed by the weight of the heart . Adapters are available for the inlet and outlet lines that permit temperature monitoring probes to be inserted easily. *

Methods All patients were operated upon with conventional techniques, including moderate systemic hypothermia to 30° C. Myocardial temperature was monitored continuously during cardiopulmonary bypass with a needle thermistor probe inserted 1.5 em into the anterior portion of the interventricular septum, the most difficult area to cool with saline pericardial lavage. Posterior wall temperatures were monitored only occasionally, to confirm that they remained below anterior septal tem·Shiley Inc.. Irvine. Calif.

Fig. 2. The jacket is in place around the heart and completely encloses both ventricles. The inlet and outlet tubes exit at the lowest portion of the sternotomy incision, outside the operative field . Access to the atria and aorta is unimpeded . peratures. The temperature of the fluid circulating in the jacket was monitored in the inlet and outlet tubes. When the temperature of the systemic perfusate reached 30° C, the aorta was clamped and I L of an asanguineous cardioplegia solution was injected. The jacket was placed around the heart at the time of the initial infusion of cardioplegia solution, unless concomitant coronary artery bypass was required, in which case the distal coronary anastomoses were completed before the jacket was secured in place. The entire cardiac procedure was often completed without reinfusion of cardioplegia solution. When mitral valve replacement was performed, the left atrial incision was closed before the aortic clamp was removed because the jacket lessened our concern

The Journal of Thoracic and Cardiovascular Surgery

8 80 Bonchek and Olinger

Table I. Clinical results with the myocardial protection jacket in 30 consecutive patients operated upon in a 3 month period

Operation MVR* AVR MVR, AVR* MVR, CAB AVR, CAB MC AD

No. of patients

Aortic clamp time (min) Mean

I

Range

Operative death

Inotropic drugs

Operative MI

1 0 0 0 0 0 0

0 0 0 0 0 0 0

46-103 64-97 95-158 86-120 95-104

1

63 79 117 103 100 19 67

1 0 0 0 0 0 0

30

81

46-158

1 (3.3%)

8 11 4 2 3 I

0

Legend: MI, Myocardial infarction. MVR, Mtral valve replacement. AVR, Aortic valve replacement. CAB, Coronary artery bypass. MC, Mitral commissurotomy. AD, Ascending aortic dissection.

·Two patients required tricuspid annuloplasty with a Carpentier ring; one with MVR, the other with AVR and MVR.

about prolonged ischemic arrest. Similarly, in patients who underwent concomitant aortic valve replacement and coronary artery bypass, the proximal coronary anastomoses were often carried out with the aorta cross-clamped if a partial occlusion clamp could not be applied easily and safely. The jacket was initially assessed in a nonconsecutive series of 10 patients while changes in design were being made. The current jacket system was used in a consecutive series of 30 patients with valvular disease or aortic aneurysms between Oct. 1 and Dec. 31, 1980. The jacket was therefore used in a total of 40 patients prior to preparation of this report. Operative death was defined as any death occurring during the period of hospitalization for the operation, or within 30 days, whichever was longer. Postoperative infarction was defined as the development of new Q waves with duration greater than 0.04 second. Inotropic support was defined as any infusion of an inotropic drug other than digoxin or a single bolus of calcium chloride. Results In the initial nonconsecutive series of 10 patients, there were no deaths, perioperative infarctions, or infusions of inotropic drugs. Results in the consecutive series of 30 patients operated upon in the recent 3 month period are depicted in Table I. The only operative death occurred in a patient with end-stage mitral valve and coronary disease who was dyspneic at rest while receiving oxygen. She had systemic pressures (120 mm Hg) in the right ventricle that did not decline after mitral valve replacement and myocardial revascularization, and she could not be weaned from cardiopulmonary bypass. There were no other deaths or

perioperative infarctions, and no other patient required inotropic support, despite long cross-clamp times on a teaching service in many patients with challenging technical problems such as endocarditis, calcified aortas, or reoperation to replace failed porcine valves. Table II displays the temperatures in the myocardium and the circulating fluid in 10 patients selected because data were reasonably complete, the patients had a wide range of periods of myocardial ischemia, and cardioplegia solution was rarely reinfused. In Patients 5, 8, and 9 the jacket lowered myocardial temperature further than did the initial injection of cardioplegia. Myocardial temperatures (anterior septum) usually remained below 14° C regardless of the length of ischemic arrest, even when cardioplegia solution was not reinfused. We found that a flow rate of 120 cc/min provided the lowest obtainable temperature in the circulating fluid (3.5 to 7° C) and the smallest temperature rise from inlet to outlet of the jacket (2° to 3° C). With the latest jacket design and the optimum flow rate of 120 cc/min, anterior septal temperatures were often maintained between 6.5 and 11° C. We also found that we could often begin to rewarm the systemic perfusate before the aortic clamp was removed, because the jacket insulated the heart from the warming effect of the blood in the thoracic aorta. In Patients 4, 5, 7, and 9, rewarming was begun 15 minutes before the final temperature recorded in Table II. None of the patients displayed evidence of phrenic nerve paralysis, which has been attributed to freezing of the nerve by saline slush in the pericardium." Discussion Countless investigators have demonstrated the importance of hypothermia in myocardial preservation.': 12-14

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881

Table II. Myocardial temperatures during aortic clamping in 10 representative patients * Patient No.

Fluid temperatures (0 C)

Ischemic time (min) Procedure(s)

CP

15

MVR

., 8.2

10.3

2

AVR MVR

10.7

10.7

10.4

10.0

9.5

10.0

9.2

3

AVR CAB

9.6

10.2

10.3t

6.4

6.9

6.6

8.2

4

AVR MYEC CAB

N.A.

N.A.

1O.9t

7.8

7.0

6.5:1:

7.0

5

MVR

11.2

10.1

8.0

8.8:1:

13.2

6

MVR

9.3 7.7

11.4 11.5

12.9 11.2

N.A.

ant. post.

I

30

I

45

I

60

I

75

I

90

I

105

Myocardial temperatures (0 C) 9.3 10.5

9.3

7.5

Inlet

I

Outlet

6.9-8.6

10.5-11.4

N.A.

N.A.

4.1-7.7

6.7-13.1

3.4-6.1

6.6-9.9

4.3-7.2

7.2-10.1

6.4-9.5

9.7-12.1

9.5

7

AVR

7.4

10.2

10.3

9.7+

11.0

5.0-9.3

7.1-11.1

8

AVR MVR

17.6

10.8

10.2

11.I§

11.3

6.6-8.6

10.5-11.4

9

AVR MVR

15.0

12.8

10.3

8.2

3.8-7.7

6.7-10.8

10

MVR

17.3

14.0

12.0

11.4:1:

N.A.

N.A.

6.8§ 12.0

7.5:1:

9.4

Legend: CP, Cardioplegia infusion. MVR, AVR, and CAB, same as in Table I. MYEC, Myectomy for idiopathic hypertrophic subaortic stenosis. N.A., Not

available. ant., Anterior septum. post., Posterior free wall of left ventricle. • Cardioplegia solution was infused only once (CP) in each patient, except in Patients 8 and 9 as noted. In Patients 3 and 4, the jacket was applied after 30 minutes of ischemic arrest. tJacket applied after distal coronary anastomoses were completed. :I: Systemic rewarming begun. §Cardioplegia reinfused.

but the standard technique described by Shumway of topical hypothermia by pericardial lavage with cold electrolyte solution has many disadvantages, as noted earlier. Moreover, during reoperations, cold lavage of the heart may be almost completely ineffective if the pericardial sac is incomplete after dissection of the heart. The myocardial protection jacket appears to overcome most of the aforementioned problems: It achieves a more profound degree of myocardial cooling than can be obtained by the pericardial lavage technique; it maintains this hypothermia indefinitely, except perhaps in the most central portion of the septum, which we did not assess; it provides cooling of the right ventricle and anterior septum; it insulates the posterior wall of the left ventricle from the thoracic aorta; it eliminates the noise of continuous suction in the pericardial space; it prevents waste of pericardial blood; and it does not require an intact pericardial sac. It is also cost-effective, as it eliminates the need for multiple bottles of electrolyte solution. In this series of patients, cardioplegic solution was rarely reinfused by one of us (L. I. B.) so that the

effectiveness of the jacket could be stringently tested. Although there may be some theoretical advantage to repeated washing out of acid metabolites, this advantage is reduced at very low myocardial temperatures and has been demonstrated primarily in experimental preparations in which the hearts were maintained above 20° C. 5, 15 Tyers and associates 12 found that myocardial protection was best below 15° C. Wilson and coworkers':' found little additional metabolic benefit from potassium cardioplegia at myocardial temperatures of 17° C. There are distinct advantages to limiting the number of cardioplegic infusions, since this limits the degree of hemodilution and prevents potential damage to the endothelium of aorta-coronary artery vein bypass grafts by high concentrations of potassium. 17, is There is also evidence to suggest that postoperative arrhythmias are more common after infusion of cardioplegic solutions with high concentrations of potassium. 19 We have found the jacket convenient to use. It is prepared by the scrub nurse in cooperation with the perfusionist, just as they prepare the tubing and con-

8 8 2 Bonchek and Olinger

nections for cardiopulmonary bypass; when the surgeon is ready to insert the jacket it is already primed with cold circulating fluid. Although the jacket has been available in only one size thus far, this has proved appropriate for most hearts, since they are completely empty while the jacket is in use and the Velcro fastener allows adjustment of the jacket's circumference.

Addendum Since submission of the manuscript, we performed a mitral valve replacement in a Jehovah's Witness with the aid of the jacket. The jacket's benefits are particularly helpful in such patients, as hemodilution is minimized by the avoidance of repeated cardioplegia infusions and loss of pericardial blood.

2

3

4

5

6

7

REFERENCES Levitsky S: Intracoronary perfusates for myocardial protection. Ann Thorac Surg 24:297, 1977 Jacocks MA, Fowler BN, Chaffiks, et al: hypothermic ischemic arrest versus hypothermic potassium cardioplegia in man. Circulation 62:Suppl 3:324, 1980 Ellis RJ, Mangano DT, VanDyke DC, Ebert PA: Protection of myocardial function not enhanced by high concentrations of potassium during cardioplegic arrest. J THORAC CARDIOVASC SURG 78:698-720, 1979 Rosenfeldt FL, Watson DA: II. Interference with local myocardial cooling by heat gain during aortic cross clamping. Ann Thorac Surg 27:13-16, 1979 Follette DM, Mulder DG, Maloney JV, Buckberg GD: Advantages of blood cardioplegia over continuous coronary perfusion or intermittent ischemia. Experimental and clinical study. J THORAC CARDIOVASC SURG 76:604-619, 1978 Shapira N, Kirsh M, Jochim K, Behrendt DM: Comparison of the effect of blood cardioplegia to crystalloid cardioplegia on myocardial contractility in man. J THoRAc CARDIOVASC SURG 80:647-655, 1980 Singh AK, Farrugia R, Teplitz C, et al: Electrolyte versus blood cardioplegia. Randomized clinical and myocardial ultrastructural study. Circulation 62:Suppl 3:324, 1980

The Journal of Thoracic and Cardiovascular Surgery

8 Stiles QR, Hughes RK, Lindesmith GG: The effectiveness of topical cardiac hypothermia. J THORAC CARDIOVASC SURG 73:176-180, 1977 9 Rosenfeldt FL, Watson DA: I. Development of an in vitro model of myocardial cooling. A study of the effect of cardiac size on cooling rate. Ann Thorac Surg 27:7-12, 1979 10 Braimbridge MV: Discussion of Ellis et aj19 II Marco JD, Hahn JW, Barner HB: Topical cardiac hypothermia and phrenic nerve injury. Ann Thorac Surg 23:235-237, 1977 12 Tyers GFO, Williams EH, Hughes HC, Todd GJ: Effect of perfusate temperature on myocardial protection from ischemia. J THoRAc CARDIOVASC SURG 73:766-771, 1977 13 Ellis RJ, Pryor W, Ebert PA: Advantages of potassium cardioplegia and perfusion hypothermia in left ventricular hypertrophy. Ann Thorac Surg 24:299-306, 1977 14 Wilson GJ, Robertson JM, Walters FJM, Steward DJ, MacGregor DC: Intramyocardial pH during elective arrest of the heart. Relative effects of hypothermia versus potassium cardioplegia on anaerobic metabolism. Ann Thorac Surg 30:472-481, 1980 15 Rosenfeldt FL, Hearse OJ, Cankovic-Darracott S, Braimbridge MV: The additive protective effects of hypothermia and chemical cardioplegia during ischemic cardiac arrest in the dog. J THORAC CARDIOVASC SURG 79:29-38, 1980 16 Rosenfeldt FL, Watson DA: III. Local cardiac hypothermia. Experimental comparison of Shumway's technique and perfusion cooling. Ann Thorac Surg 27:17-23, 1979 17 Carpentier S, Murawsky M, Carpentier A: Cyto-toxicity of cardioplegic solutions. Evaluation by tissue culture. Circulation 62:Suppl 3:324, 1980 18 Hoover E, Pelt S, Eldor A, et al: Cardioplegic solutionassociated fibrosis of canine vein grafts in vivo with preservation of vascular prostacyclin production. Circulation 62:Suppl 3:324, 1980 19 Ellis RJ, Mavroudis C, Gardner C, Turley K, Ullyot D, Ebert PA: Relationship between atrioventricular arrhythmias and the concentration of K+ ion in cardioplegic solution. J THORAC CARDIOVASC SURG 80:517-526, 1980