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Ann Thorac Surg 1995;60:156-159
© 1995 The Society of Thoracic Surgeons

Conversion of Postischemic Ventricular Fibrillation With Intraaortic Infusion of Potassium Chloride

Eivind Øvrum, MD, Geir Tangen, MD, Einfrid Åm Holen, MD, Mari-Anne L. Ringdal, CCP, Reidar Istad, CCP

Departments of Cardiac Surgery and Anesthesiology, Oslo Heart Center, Oslo, Norway

Accepted for publication March 17, 1995.


   Abstract
Top
 Footnotes
 Abstract
Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
Background. Ventricular fibrillation after declamping of the aorta after cardioplegic arrest is commonly managed by direct-current countershock. However, in coronary artery bypass grafting, placement of the electrodes can cause mechanical damage to the grafts and anastomoses, and the surgical procedure must be interrupted. As an alternative, intraaortic infusion of potassium chloride through the arterial line from the heart-lung machine was investigated.

Methods. In a series of 100 patients with postischemic ventricular fibrillation (group P), 20 mmol of potassium chloride (plus 10 mmol later if necessary) was added to the oxygenator reservoir and perfused through the arterial line into the proximal aorta. The results were compared with those in a matched control group of 100 patients primarily treated with direct-current countershock (group DC).

Results. In group P, the ventricular fibrillation was effectively converted to a supraventricular rhythm in 82% of the patients. The remaining 18 patients required significantly (p < 0.005) fewer electric shocks than the patients in group DC. Serum K+ levels were slightly elevated for a short period after the potassium chloride infusion. Otherwise there were no significant differences in regard to incidence of heart block, temporary epicardial pacing, myocardial infarction, or atrial fibrillation between the two groups.

Conclusions. Conversion of postischemic ventricular fibrillation with potassium chloride administered through the arterial line from the heart-lung machine is an effective, gentle, and convenient method. No side effects were noted.


   Introduction
Top
 Footnotes
 Abstract
 Introduction
Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
Ventricular fibrillation is common after declamping of the aorta after cardioplegic arrest. Conventional management consists of defibrillation with direct-current countershock by placement of intrapericardial electrodes. However, the electric energy applied to the heart has been demonstrated to cause myocardial damage [1]. Moreover, applying paddles of substantial size to a cardiac surface with several coronary anastomoses and grafts is potentially hazardous and can cause disruption, and the surgeon must interrupt the operation.

As an alternative, intraaortic infusion of potassium chloride through the arterial line from the heart-lung machine has proved effective to defibrillate the heart. This approach is based on the fact that total exchangeable potassium as well as the concentration of intracellular potassium is decreased during and after extracorporeal circulation [2] and on the fact that extracellular potassium has a depolarizing effect on the cellular membrane. The present study includes our initial experience with this technique in patients undergoing coronary artery bypass grafting.


   Material and Methods
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
Results
 Comment
 Acknowledgments
 References
 
During the 5-year period 1989 through 1993, the incidence of postischemic ventricular fibrillation in our institution was 20.3% (501/2,470 patients). In the remaining 79.7%, a supraventricular rhythm, mostly sinus rhythm, returned spontaneously. For patients with ventricular fibrillation during reperfusion, the potassium conversion method was introduced in August 1992. A relatively small amount of potassium chloride was added to the oxygenator reservoir and perfused through the arterial line from the heart-lung machine into the aortic root.

Patient Population
The cases of the first 100 patients (group P) in our database who had ventricular fibrillation after aortic declamping and received potassium conversion were retrospectively studied. In this group, if ventricular fibrillation persisted for more than 2 minutes during reperfusion, 20 mmol of potassium chloride was added to the oxygenator reservoir, the volume having been reduced to 350 to 400 mL. The volume was rapidly infused through the arterial line into the aortic cannula, and performance of the proximal anastomoses continued unaffected by this procedure. If conversion to a supraventricular rhythm was unsuccessful, another 10 mmol was added, and if ventricular rhythm still persisted, direct-current countershocks were given.

Another 100 patients operated on by the same surgeons in the period immediately before initiation of the potassium conversion method served as the control group (group DC). In this group electric countershock was the primary and only treatment of ventricular fibrillation.

In both groups, the success rate of ventricular fibrillation conversion in terms of the treatment applied was recorded. The levels of serum potassium were measured before removal of the aortic cross-clamp and at 10, 20, and 120 minutes thereafter. The simultaneous serum pH was noted. Arterial line and rectal temperatures were recorded at the time of aortic declamping. The incidence of heart block, use of a pacemaker, episodes of atrial fibrillation, and all in-hospital complications were recorded.

Operation
Standard operative procedures included aortic cross-clamping during performance of the distal anastomoses. Myocardial protection consisted of antegrade crystalloid cardioplegia and topical cooling with ice slush. Procaine chloride was an essential component of the cardioplegic solution, the composition of which was as follows:

The proximal anastomoses were sutured during partial occlusion of the ascending aorta during rewarming. In addition to saphenous vein grafts, at least one internal mammary artery anastomosis was constructed in all except 3 patients.

The anesthesia protocol included a combination of diazepam (0 to 0.2 mg/kg), midazolam hydrochloride (0 to 0.2 mg/kg), fentanyl (6 to 8 µg/kg), and pancuronium bromide, supplemented with isoflurane and nitrous oxide.

Extracorporeal circulation was performed using pulsatile flow at a rate of 2.4 L • m-2 • min-1, and mild hypothermia (blood temperature, 32°C) was instituted immediately after the start of bypass. The heart-lung machine was primed with 2,000 mL of Ringer's acetate. A hard-shell oxygenator reservoir was standard in the circuit.

Statistical Analysis
Comparison of the two groups was done using the Mann-Whitney test for continuous variables. Discrete variables were treated by means of contingency tables, with Yates' correction and Fisher's test when one of the expected cell values was less than 5. Data are shown as the mean ± the standard deviation. A p value of less than 0.05 was considered significant. All data were registered prospectively and stored in a database (Dbase IV).


   Results
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Results
Comment
 Acknowledgments
 References
 
The demographic data were comparable for all major variables except that the mean age in group P was somewhat higher than that in group DC (Table 1Go). There were no differences in operative data (Table 2Go), and no differences were noted in regard to rectal and arterial temperatures at the time of aortic declamping.


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  		Table 1. . Demographic Data on the Two Patient Groupsa
 

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  		Table 2. . Summary of Operative Data on the Two Patient Groupsa,b
 
The effects of the type of treatment of the ventricular defibrillation are shown in Table 3Go. In group P, 82 patients were successfully converted with intraaortic infusion of potassium chloride. In 72 of them, conversion was accomplished with 20 mmol of potassium chloride, and in 10, supraventricular rhythm occurred after an additional 10 mmol. In the remaining 18 patients, ventricular fibrillation was converted with one to three direct-current countershocks (8 to 20 W). In these patients, the mean aortic cross-clamping time was 24.7 ± 11.5 minutes compared with 29.0 ± 10.3 minutes in the other 82 patients (p = 0.2). The mean arterial temperature at aortic declamping was significantly lower in the patients requiring countershocks compared with those whose conversion with potassium chloride was successful (38.4° ± 0.6°C versus 38.8° ± 0.8°C; p = 0.01).


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  		Table 3. . Treatment of Ventricular Fibrillation and Serum Level of K+ in the Two Groupsa
 
As expected, the mean serum level of K+ was significantly higher in group P 10 minutes after the potassium infusion compared with the DC group (5.5 ± 1.0 mmol/L versus 4.3 ± 0.4 mmol/L; p < 0.01) and scarcely exceeded the upper normal level. After another 10 minutes, the levels in the two groups were similar and within normal ranges (see Table 3Go). At 120 minutes, the serum K+ level was significantly higher in group P, but this was not of clinical importance. The simultaneous serum Ph values were identical in the two groups at all times.

In group DC , the success rate of the initial countershock was 66%. In the remaining 34% of patients, an additional 1 shock to 6 shocks was necessary to convert the ventricular fibrillation. The number of countershocks required for conversion was significantly higher (p < 0.005) compared with the number necessary for conversion in group P.

Intraoperatively, the incidence of temporary epicardial pacing was somewhat lower in group DC than in group P, but the difference was not significant (Table 4Go). There was no correlation between number of countershocks and incidence of heart block, as only 1 patient having more than three shocks needed a pacemaker.


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  		Table 4. . Summary of Postoperative Data on the Two Patient Groupsa
 
In the postoperative period, 1 patient in each group was pacemaker dependent for some hours because of bradycardia (see Table 4Go). The incidence of perioperative myocardial infarction and the number of episodes of atrial fibrillation were similar in both groups. One patient in group P died. Death was not related to the treatment of the ventricular dysrhythmia.


   Comment
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
Acknowledgments
 References
 
Ventricular fibrillation during the reperfusion period after removal of the aortic cross-clamp can adversely affect coronary blood flow and may contribute to subendocardial ischemia and depressed ventricular performance [3]. The energy needed for electric conversion of ventricular fibrillation has been shown to damage the myocardium [1]. Therefore, prevention of ventricular fibrillation should be the primary goal. We routinely use procaine chloride as an essential component of our cardioplegic solution, and the overall incidence of spontaneous supraventricular rhythm is about 80% in patients undergoing myocardial revascularization. This compares well with the findings in other reports using alternative local anesthetics such as lidocaine hydrochloride either in the cardioplegic solution [4] or in the extracorporeal circuit [5]. Further, the incidence of spontaneous sinus rhythm is similar to that reported with warm blood cardioplegia [6] and exceeds markedly the incidence recognized with cold blood cardioplegia [4, 6].

The mechanisms of converting ventricular fibrillation with potassium chloride in the present setting may be due to several factors. Hyperkalemic blood perfused into the ascending aorta acts in a similar fashion as cardioplegic solution administered into the aortic root with subsequent membrane depolarization. In fact, the initial effect seen in the surgical field is a few seconds of cardiac arrest before recovery of a supraventricular rhythm. Pacifico and associates [2] demonstrated that both exchangeable and intracellular potassium levels are decreased after cardiopulmonary bypass. The short and rapid increase in the extracellular level of potassium in a hypokalemic situation is assumed to improve membrane stabilization of myocytes in the critical phase of reperfusion. This may explain our observations in the subset of patients whose conversion was not successful with potassium chloride. The number of countershocks required for defibrillation after potassium infusion was significantly smaller (p < 0.005) compared with the number in the control group, which was primarily treated with direct-current countershocks (see Table 3Go). On the other hand, one reason supraventricular rhythm was not always accomplished with potassium chloride, may be the lower arterial temperatures recorded in this subgroup. We also emphasize the importance of reducing the residual volume in the reservoir before adding the potassium. This maneuver is mandatory to ensure adequate potassium concentration in the infused blood, and variations in this procedure may influence the rate of success.

The beneficial effects of reducing the application of electric energy to the myocardium are related to the extent of potential injury. Dahl and associates [1] clearly demonstrated substantial myocardial damage to hearts given multiple electric countershocks. In our clinical setting with a cardioplegic solution containing procaine chloride, the initial incidence of ventricular fibrillation after declamping is about 20% of all patients. Conversion of the ventricular rhythm with potassium chloride is successful in approximately 80% of patients. This leaves only 4% of the total patient population requiring conversion with direct-current countershocks.

The plasma level of K+ was significantly elevated 10 minutes after the intraaortic potassium infusion. The increase was modest and normalized after a short time. This elevation might be correlated to the trend, although it was not significant, toward a higher incidence of heart block and a greater use of epicardial pacing immediately after infusion of potassium chloride. However, the conduction disturbances were of short duration, and at arrival in the intensive care unit, only 1 patient in each group was dependent on a pacemaker for some hours.

Use of intraaortic infusion of potassium chloride to treat ventricular fibrillation has not been widely reported, although we are aware that the method has been used routinely for many years in some European cardiac centers (Robert Dion: personal communication, May 1994). Our data demonstrate that this optional method for converting ventricular fibrillation is effective, gentle, and safe. When successful, the surgeon can proceed with the operation without interruption and without the inconvenience of placing large electrodes on the cardiac surface. Consequently, we have adopted this technique for coronary artery bypass procedures. Our experience is limited to relatively low-risk patients with normal organ functions, and care should be taken in patients with renal failure.


   Acknowledgments
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
References
 
We thank Rolf Øystese, CCP, and Brita Noorland, RN, for skillful technical assistance.


   Footnotes
Top
 Footnotes
Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 
Address reprint requests to Dr Øvrum, Oslo Heart Center, Pilestredet 32, 0027 Oslo, Norway.


   References
Top
 Footnotes
 Abstract
 Introduction
 Material and Methods
 Results
 Comment
 Acknowledgments
 References
 

  1. Dahl CF, Ewy GA, Warner ED, Thomas ED. Myocardial necrosis from direct current countershock. Circulation 1974;50:956–61.[Abstract/Free Full Text]
  2. Pacifico AD, Digerness S, Kirklin JW. Acute alterations of body composition after open intracardiac operations. Circulation 1979;41:331–41.[Abstract/Free Full Text]
  3. Ciardullo RC, Schaff HV, Flaherty JT, Gott VL. Myocardial ischemia during cardiopulmonary bypass. J Thorac Cardiovasc Surg 1977;73:746–57.[Abstract]
  4. Fiore AC, Naunheim KS, Taub J, et al. Myocardial preservation using lidocaine blood cardioplegia. Ann Thorac Surg 1990;50:771–5.[Abstract]
  5. Fall SM, Burton NA, Graeber GM, et al. Prevention of ventricular fibrillation after myocardial revascularization. Ann Thorac Surg 1987;43:182–4.[Abstract]
  6. Christakis GT, Koch JP, Deemar KA, et al. A randomized study of the systemic effects of warm heart surgery. Ann Thorac Surg 1992;54:449–59.[Abstract]



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Right arrow Articles by Øvrum, E.
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