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Clinical Investigations: SURGERY |

Potassium Supplementation, Diet vs Pills*: A Randomized Trial in Postoperative Cardiac Surgery Patients FREE TO VIEW

Wendi Norris; Karyn S. Kunzelman; Susan Bussell; Linda Rohweder; Richard P. Cochran
Author and Funding Information

Affiliations: *From the Division of Cardiothoracic Surgery, University of Washington, Seattle, WA.,  Present affiliation: Central Maine Heart and Vascular Institute, Lewiston, ME.,  Present affiliation: Eastern Idaho Regional Medical Center, Idaho Falls, ID.

Correspondence to: Wendi Norris, MD, MSW, Division of Pulmonary and Critical Care Medicine, University of Washington, Box 359762, 325 Ninth Ave, Seattle, WA 98104; e-mail: wnorris@u.washington.edu



Chest. 2004;125(2):404-409. doi:10.1378/chest.125.2.404
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Background: Cardiac surgery patients are commonly treated with diuretics, which can result in hypokalemia requiring potassium supplementation.

Objective: Our objective was to determine whether cardiac surgery patients receiving therapy with potassium-wasting diuretics can safely and beneficially maintain serum potassium levels by eating potassium-rich foods.

Design: A prospectively randomized trial of diet vs medication supplementation of potassium was undertaken. Patients who were to undergo cardiac surgery and who would be receiving therapy with oral furosemide postoperatively were eligible for the study. Forty-eight patients were enrolled in the trial, and 38 patients completed the study. Patients received either potassium-rich foods (diet) or potassium chloride pills (medication).

Results: There was no significant difference in mean (± SD) serum potassium concentrations between groups preoperatively (4.25 ± 0.30 vs 4.29 ± 0.33 mEq/L, respectively), on postoperative day 3 (4.23 ± 0.40 vs 4.27 ± 0.40 mEq/L, respectively), or postoperative day 4 (4.23 ± 0.48 vs 4.24 ± 0.33 mEq/L, respectively) for the diet and medication groups. Length of stay was significantly lower in the diet group (5.0 ± 0.9 vs 6.3 ± 2.2 days, respectively). When asked their preferences for method of supplementation, 79% of patients preferred the diet method.

Conclusions: Cardiac surgery patients receiving therapy with diuretics can maintain serum potassium levels at clinically adequate concentrations by eating potassium-rich foods. Length of stay was significantly reduced. This method of potassium supplementation demonstrates the potential for reduced costs and increased patient satisfaction.

Figures in this Article

Patients who undergo cardiac surgery are commonly treated with diuretic therapy for the management of volume overload, pulmonary edema, and peripheral edema. While there are many pharmacologic choices available, furosemide (a loop diuretic) is frequently used in the cardiac surgery setting. The desired result of furosemide treatment is increased excretion of sodium and water, however, this disturbs the normal potassium balance, resulting in hypokalemia.12 Thus, potassium supplementation is generally necessary when administering furosemide therapy to patients.

The usual method of potassium supplementation, oral administration of potassium chloride tablets, has been shown to have several negative consequences. Historically, these tablets were quite large and difficult to swallow, making it difficult for patients to take the pills. Once smaller tablets became available, patients expressed distress about the number required for adequate potassium supplementation. Additionally, regardless of pill size, a frequent side effect of potassium supplementation is GI distress, including nausea and vomiting.34 For these reasons, some patients refuse to take the pills, resulting in hypokalemia and potentially prolonged hospital stays. In addition, in some patients who are willing to take the pills, the magnitude of the GI distress may also result in prolonged hospitalization. The negative response of the patients toward potassium chloride tablet supplementation, the GI side effects, and the potential impact on length of stay, prompted us to evaluate alternative methods of potassium supplementation in cardiac patients.

An alternative to potassium salt supplements is adjusting the diet to increase the intake of potassium-rich food.5 There are published articles68 that propose using the intake of potassium-rich foods as means of maintaining serum potassium concentrations while using diuretics. However, there are no studies that address the efficacy or safety of this approach. Therefore, the first hypothesis in our study was that cardiac surgery patients receiving furosemide could maintain their serum potassium levels at clinically adequate concentrations by eating potassium-rich foods. Furthermore, we hypothesized that the dietary supplementation would decrease GI distress and thereby shorten the hospital stay.

The hypotheses were tested in a randomized, controlled trial of patients undergoing cardiac surgery at the University of Washington Medical Center. Consecutive patients who were to undergo cardiac surgery using a bypass pump and who would be receiving oral furosemide postoperatively were eligible for the study. All patients were using the bypass pump for the procedure, which included coronary artery bypass graft (CABG), valve replacement or repair, or CABG and valve replacement. Informed consent was obtained, and the procedures followed were in accord with the ethical standards of the University of Washington Institution Review Board (approval No. 25-728-A). Patients were excluded for any of the following conditions: (1) they were not fluent in English; (2) they were receiving hemodialysis preoperatively; (3) they had experienced nausea and vomiting for > 24 h; or (4) they received oral furosemide doses of > 160 mg/d. Enrolled patients whose potassium level fell to < 3.5 mEq/L were dropped from the study protocols and were given parenteral potassium replacement.

Randomized Trial

For the study, 40 patients were prospectively randomized into a diet or medication group, and 38 patients completed the study protocol. Table 1 shows the baseline characteristics and comorbid conditions of each group. The two groups were of similar ages. There is a predominance of male participants, because this procedure is more common in men. The medication group took on average more furosemide than the diet group. The distribution of preoperative comorbidities was similar. Eight additional patients were initially enrolled into the diet group but were excluded from analysis. Three patients asked to stop their participation in the study. One thought that he was “not getting enough protein” with the standardized meal. One thought that the potassium-rich foods “caused increased gastric secretion.” The third did not give a reason for withdrawal. Four patients were excluded because they received potassium chloride pills due to nursing noncompliance with the protocol. The last of the eight patients excluded from analysis was excluded because she became confused and was unable to take anything orally, which negated the possibility of dietary supplementation.

Patients were approached for participation in the study by either of two investigators (WN or SB). Randomization was performed by computer program, and notification of randomization pick was performed by a third individual. At the time of consent, the patients were asked to complete a brief questionnaire about how they would prefer to take potassium supplementation (ie, diet vs medication). At the end of the trial, those patients in the diet cohort were queried as to whether they thought they would feel comfortable continuing diet supplementation outside of the hospital. The trial was not blinded, since there were obvious differences between receiving dietary supplementation, in which patient food choice was involved, vs receiving medication in the form of a tablet. If a patient was dropped from the study, the next patient who agreed to participate in the study was placed in the same study group as the dropped participant, and random allocation was resumed for the next enrolled patient.

Furosemide and Potassium Dosing

All patients were receiving therapy with oral furosemide for diuresis after surgery. The standard concomitant potassium chloride dose is equivalent to half the furosemide dose per day. Thus, in this study, a “medication patient” receiving 60 mg furosemide per day received 30 mEq of potassium by taking oral potassium chloride medication. In contrast, a “diet” patient on an equivalent furosemide dose received 30 mEq of potassium in potassium rich foods instead. Potassium replacement, by either diet or medication, was initiated at the same time as the oral loop diuretic. The treating surgeons determined timing of the initiation of the loop diuretic. All patients started receiving therapy with diuretics by postoperative day 3. Each “diet patient” chose his or her own potassium-rich foods from a standardized list (Table 2 ).911 If a subject’s serum potassium level fell to < 3.8 mEq/L, the potassium dose was increased to 75% of their furosemide dose. A standardized meal plan was implemented for both groups to ensure that patients were not getting potassium from unknown sources. The average nutritional content for daily intake included protein (98 g), fat (81 g), carbohydrate (279 g), sodium (2.3 g), and potassium (106 mEq). The daily energy content was 2,200 calories. To ensure safety, subjects were monitored on remote cardiac telemetry for cardiac arrhythmia, which is standard protocol.

Outcomes and Statistical Analysis

Patient participation in the study started on the initiation of oral furosemide therapy and was stopped on discharge from the hospital. As the primary study outcome, serum potassium concentrations were obtained preoperatively, and on postoperative day 3. Additionally, if possible, the serum potassium concentration was obtained on subsequent postoperative days (prior to discharge). Secondary study outcomes included the following: number of medications (ie, preoperative, postoperative, and on hospital discharge); complications (ie, nausea, vomiting, and hypokalemia [potassium level < 3.5 mEq], atrial fibrillation, ventricular tachycardia, and need for a pacemaker); and length of stay. In addition, on initiation of the study protocol each patient was asked whether they would prefer to eat a dietary supplement or to take a pill. In addition, if the patient was in the diet group, at hospital discharge each was asked whether they would feel safe continuing the potassium-rich diet at home. Parametric data were compared using t tests, and nonparametric data were compared using the Wilcoxon rank sum test. Length-of-stay data were compared by analysis of variance. A p value of < 0.05 was considered to be significant.

Thirty-eight patients completed the study. Data are presented for 39 patients because the potassium of 1 diet patient dropped to < 3.5 mEq on postoperative day 3. This patient received parenteral potassium chloride therapy, per protocol, and was dropped from the study protocols, but this patient’s data are included in the analysis as intention to treat. The reasons for not completing the study are shown in Figure 1 . Another diet patient received a furosemide dose of > 160 mg/d on day 4, as more diuresis was needed. This patient was also dropped from the study, as exclusion criteria were met. For all remaining patients (38 patients), the average daily furosemide dose was 84 mg/d. The procedures that patients underwent were varied, but all had used a bypass pump. Twenty-five participants had undergone CABG procedures, and an additional 3 patients had to undergo redo CABG. Four participants underwent aortic valve replacement, and an additional patient underwent redo aortic valve replacement. Two participants each underwent mitral valve replacement and mitral valve repair. One participant each had a Ross procedure, a CABG, and aortic valve replacement, and a CABG and mitral valve repair.

There was no significant difference in the average serum potassium concentrations between groups preoperatively, or on postoperative day 3 or 4 (Table 3 ). One patient in the diet group and one patient in the medication group did not have blood drawn on day 3. While the day 3 concentrations are slightly lower for each group compared to its respective preoperative concentration, the decreases are not statistically significant.

The number of complications was within the expected range for postoperative cardiac patients. First, no patients in either group experienced nausea or vomiting during the study. Second, all but one patient maintained their serum potassium concentrations at > 3.5 mEq/L. There were four episodes in three patients in the diet cohort when the serum potassium concentration dropped to < 4.0 mEq/L, compared to nine episodes in nine patients in the medication group (p = 0.10).

Several patients who participated in the study had complications that often are associated with heart disease and cardiac surgery. One patient had a pacemaker placed postoperatively. She was a patient in the medication group who had no potassium drops to < 4.0. Four patients went into atrial fibrillation during their hospital stay (10.3% of the patients participating in the study). Of the patients who went into atrial fibrillation, three were diet group participants (15.8%), and one was a medication group participant (5%). This difference was not statistically significant. One of the diet patients who went into atrial fibrillation had a potassium concentration drop to < 4.0 mEq/L, while the other two did not. The medication group patient who went into atrial fibrillation had a potassium drop to < 4.0 mEq/L. One patient went into nonsustained ventricular tachycardia following atrial fibrillation. He was a diet group patient who had no potassium drops to < 4.0 mEq/L. This one patient represents 2.6% of the studied group experiencing ventricular tachycardia. The mean length of stay for patients in the diet group was significantly less than that for the medication group (p = 0.03). The mean (± SD) length of stay for the diet group was 5.0 ± 0.91 days (range, 4 to 8 days). The average length of stay for the medication group was 6.3 ± 2.25 days (range, 4 to 15 days).

Overall, a slight majority of the patients (21 of 39 patients [54%]) were concerned about the number of medications they were taking prior to the initiation of the study. A majority of patients (31 of 39 patients [79%]) stated a preference for potassium supplements via food, rather than by potassium pill (Table 4 ). At hospital discharge, the majority of diet patients (13 of 18 patients [72%]) stated that they would feel safe taking potassium-rich foods at home for supplementation, rather than a medication.

Our study suggests that cardiac surgery patients receiving therapy with furosemide, a strong potassium-wasting diuretic, can maintain their serum potassium levels at clinically adequate concentrations by eating potassium-rich foods. The serum potassium concentrations in the diet group were not significantly different from that in the medication group, at any time point. It should be noted that we randomized a total of 28 patients into the diet group and were only able to obtain data for 19. However, the inability of the diet regimen to maintain serum potassium was not the reason for patient withdrawal in 9 of the 10 patients (Fig 1) . Data from eight patients were not included in the analyses because potassium and survey data were not collected after patients were excluded. Two of the 20 enrolled patients met the study exclusion criteria during their participation. Of these two patients, only one had the serum potassium level drop to < 3.5 mEq/L. Data from the one patient who did not maintain his serum potassium concentration at > 3.5 mEq/L is included with the intention-to-treat analysis.

Articles67 have cited the use of diet-derived potassium as the mechanism to replete potassium in patients receiving diuretics, but most did not have citations for this claim. The investigators have been unable to find a study that ensures that a diet rich in potassium is adequate to maintain serum potassium while receiving diuretics. We believe this is the first time that potassium replacement by diet and medication has been compared for efficacy. Bear and Neil6 have stated that “mild potassium deficiencies can be corrected by foods rich in the element or by supplemental potassium chloride. Most patients who are receiving thiazide diuretics need only increase their dietary intake of potassium…,” although it has been stated that there is no citation present. Bourke and Delaney7 state that hypokalemia induced by therapy with diuretics is common, and that prevention should include a low-salt diet rich in potassium, magnesium, and chloride. Saggar-Malik and Cappuccio8 cite in their article that a moderate increase in potassium intake can be achieved either by eating potassium-rich foods or by adding potassium salts to the diet. They discuss multiple reasons for hypokalemia, including diet changes with less intake of fruits and vegetables, GI losses such as vomiting, and renal losses including tubular dysfunction and diuretics. Cited is an abstract by Bull and Buss.12 Their abstract discussed the daily intake of potassium in the United Kingdom as 2.99 g per person, based on foods purchased in the United Kingdom. They did an analysis of diet samples and computed the average daily intake of potassium. The abstract does not address the daily intake of potassium in patients taking diuretics. It seems logical that a diet rich in potassium could maintain the serum potassium level of someone taking diuretics, but it has not been previously studied.

Our study demonstrated a significantly reduced length of hospital stay for the diet patients, a difference of > 1 day. In the current cost-conscious environment, this result is important. The reason for the reduced length of stay is not clear but was not due to a reduction in GI side effects. Dietary potassium supplementation affords the opportunity to decrease the number of medications that patients receive and a majority of patients in our study stated that they would prefer eating potassium rich foods rather than taking a potassium chloride pill. Since the patients have control over how they receive their potassium, the method includes them in their own health care, which may lead to greater motivation and earlier discharge.1315 The most frequently chosen foods for obtaining potassium were either through low sodium tomato juice, low sodium V8 juice, baked potatoes, or bananas, as well as salt substitute. As a further potential benefit, this involvement in diet as part of treatment may result in patients being more motivated to change their dietary habits. An additional benefit of food-derived potassium that has been previously reported may be potential prevention and control of uncomplicated mild to moderate hypertension.8

The reduced length of stay could not be shown to be directly related to the number of complications measured in this study, but the number of complications was low in both groups. Only 10% of all patients (diet, three patients; medication, one patient) went into atrial fibrillation, which is lower than most reported rates. The rate of atrial fibrillation after cardiac surgery is commonly cited to be between 10% and 30%.1618 One participant went into nonsustained ventricular tachycardia while hospitalized. He was one of the four patients who went into atrial fibrillation during the hospitalization. He was neither hypokalemic nor hyperkalemic during his hospitalization. As such, we think that dietary supplementation did not contribute to his arrhythmias. The rate of ventricular tachycardia after cardiac surgery is commonly cited to be between 2% and 20%.19

There are limitations to this study. Small sample size may contribute to a type 2 error, showing that there is no difference in potassium levels when there actually was a difference between the two groups. There was a significant difference in length of stay between the two groups. Although this is intriguing, it is difficult to explain with certainty why this was true. Given the limitation of the small sample size and the fact that potassium levels were the primary outcome of this trial, our study should be viewed as a small phase 2 trial suggesting equivalency of oral potassium supplementation via a diet method rather than potassium chloride pills, and as generating the hypothesis that the diet method may result in a decrease in the length of hospital stay. This hypothesis should be tested in future studies. Another limitation was the replacement of patients who dropped from the study with the next consenting patient, who was not randomized. This may have introduced an unintended bias, although the direction of bias is hard to determine. In those patients who requested to be dropped from the study, however, their potassium levels were between 4.1 and 4.9 mEq/L. As they requested to withdraw from the study, we do not have complete data sets to be included as intention to treat.

We have shown that dietary potassium supplementation seems to maintain adequate serum potassium concentrations in a group of cardiac surgery patients receiving therapy with oral furosemide at < 160 mg/d. The diet group demonstrated a reduced length of stay, which would reduce hospital costs. In addition, decreasing the possible side effects inherent with taking medication, the costs associated with the treatment of side effects would be reduced. Therefore, our results suggest that potassium supplementation by diet was not associated with clinically significant hypokalemia, that it involves the patient more directly in his or her own recovery, which has significant psychological benefit, and that it may have significant economic benefit by reducing the length of hospital stay. Future studies should be performed to replicate these findings.

Abbreviation: CABG = coronary artery bypass graft

Table Graphic Jump Location
Table 1. Subject Characteristics and Preoperative Comorbidities*
* 

Values given as mean ± SD or % (No. of patients), unless otherwise indicated).

Table Graphic Jump Location
Table 2. Potassium Content of Foods and Beverages*
* 

Information from Pennington,9 Computrition,10 and ServBorden.11

 

Resource Plus made by Sandoz Nutrition (Minneapolis, MN).

 

Nutrashake made by Nutra/Balance Product (Boulder, CO).

Figure Jump LinkFigure 1. Study participant enrollment and withdrawal.Grahic Jump Location
Table Graphic Jump Location
Table 3. Serum Potassium Concentrations
* 

Values given as ± SD.

Table Graphic Jump Location
Table 4. Patient Preference for Potassium Replacement (Food vs Medication)

We thank J. Randall Curtis, MD, MPH, for his thoughtful review of the manuscript.

Guyton, AC, Hall, JE (1996)Textbook of medical physiology.,408-410 WB Saunders Co. Philadelphia, PA:
 
Rose, BD, Rennke, HG Renal physiology: the essentials.1994,97-122 Williams & Wilkins. Baltimore, MD:
 
Hardman, JG, Limbird, LE, Molinoff, PB, et al The pharmacologic basis of therapeutics.1996,697-701 McGraw-Hill. New York, NY:
 
Pietro, DA, Davidson, L Evaluation of patient’s preference of two potassium chloride supplements: Slow K and K-Dur.Clin Ther1990;12,431-435. [PubMed]
 
Cohn, JN The management of chronic heart failure.N Engl J Med1996;335,490-498. [CrossRef] [PubMed]
 
Bear, RA, Neil, G A clinical approach to common electrolyte problems: potassium imbalances.Can Med Assoc J1983;129,28-31. [PubMed]
 
Bourke, E, Delaney, V Prevention of hypokalemia caused by diuretics.Heart Dis Stroke1994;3,63-67. [PubMed]
 
Saggar-Malik, AK, Cappuccio, FP Potassium supplements and potassium-sparing diuretics.Drugs1993;46,986-1008. [CrossRef] [PubMed]
 
Pennington, JA. Bowes & Churches Food: values of portions commonly used. 1994; JB Lippincott. Philadelphia, PA:.
 
 Computrition [package insert]. 1988; Computrition. Chatsworth, CA:.
 
 ServBorden Foods [package insert]. 1988; ServBorden Foods. Chatsworth, CA:.
 
Bull, NL, Buss, DH Contributions of foods to potassium intakes [abstract].Proc Nutr Soc1980;39,231A. [CrossRef]
 
Britten, N Patients’ ideas about medicines: a qualitative study in a general practice population.Br J Gen Pract1994;44,465-468. [PubMed]
 
Chewning, B, Sleath, B Medication decision making and management: a client-centered model.Soc Sci Med1996;42,389-398. [CrossRef] [PubMed]
 
Stockwell-Morris, L, Schulz, RM Medication compliance: the patient’s perspective.Clin Ther1993;15,593-606. [PubMed]
 
Mathew, JP, Parks, R, Savino, JS, et al Atrial fibrillation following coronary artery bypass graft surgery: predictors, outcomes, and resource utilization.JAMA1996;276,300-306. [CrossRef] [PubMed]
 
Yousif, H, Davies, G, Oakley, CM Peri-operative supraventricular arrhythmias in coronary bypass surgery.Int J Cardiol1990;26,313-318. [CrossRef] [PubMed]
 
Olshansky, B Management of atrial fibrillation after coronary artery bypass graft.Am J Cardiol1996;78,27-34. [CrossRef] [PubMed]
 
Gold, MR, O’Gara, PT, Buckley, MJ, et al Efficacy and safety of procainamide in preventing arrhythmias after coronary artery bypass surgery.Am J Cardiol1996;78,975-979. [CrossRef] [PubMed]
 

Figures

Figure Jump LinkFigure 1. Study participant enrollment and withdrawal.Grahic Jump Location

Tables

Table Graphic Jump Location
Table 1. Subject Characteristics and Preoperative Comorbidities*
* 

Values given as mean ± SD or % (No. of patients), unless otherwise indicated).

Table Graphic Jump Location
Table 2. Potassium Content of Foods and Beverages*
* 

Information from Pennington,9 Computrition,10 and ServBorden.11

 

Resource Plus made by Sandoz Nutrition (Minneapolis, MN).

 

Nutrashake made by Nutra/Balance Product (Boulder, CO).

Table Graphic Jump Location
Table 3. Serum Potassium Concentrations
* 

Values given as ± SD.

Table Graphic Jump Location
Table 4. Patient Preference for Potassium Replacement (Food vs Medication)

References

Guyton, AC, Hall, JE (1996)Textbook of medical physiology.,408-410 WB Saunders Co. Philadelphia, PA:
 
Rose, BD, Rennke, HG Renal physiology: the essentials.1994,97-122 Williams & Wilkins. Baltimore, MD:
 
Hardman, JG, Limbird, LE, Molinoff, PB, et al The pharmacologic basis of therapeutics.1996,697-701 McGraw-Hill. New York, NY:
 
Pietro, DA, Davidson, L Evaluation of patient’s preference of two potassium chloride supplements: Slow K and K-Dur.Clin Ther1990;12,431-435. [PubMed]
 
Cohn, JN The management of chronic heart failure.N Engl J Med1996;335,490-498. [CrossRef] [PubMed]
 
Bear, RA, Neil, G A clinical approach to common electrolyte problems: potassium imbalances.Can Med Assoc J1983;129,28-31. [PubMed]
 
Bourke, E, Delaney, V Prevention of hypokalemia caused by diuretics.Heart Dis Stroke1994;3,63-67. [PubMed]
 
Saggar-Malik, AK, Cappuccio, FP Potassium supplements and potassium-sparing diuretics.Drugs1993;46,986-1008. [CrossRef] [PubMed]
 
Pennington, JA. Bowes & Churches Food: values of portions commonly used. 1994; JB Lippincott. Philadelphia, PA:.
 
 Computrition [package insert]. 1988; Computrition. Chatsworth, CA:.
 
 ServBorden Foods [package insert]. 1988; ServBorden Foods. Chatsworth, CA:.
 
Bull, NL, Buss, DH Contributions of foods to potassium intakes [abstract].Proc Nutr Soc1980;39,231A. [CrossRef]
 
Britten, N Patients’ ideas about medicines: a qualitative study in a general practice population.Br J Gen Pract1994;44,465-468. [PubMed]
 
Chewning, B, Sleath, B Medication decision making and management: a client-centered model.Soc Sci Med1996;42,389-398. [CrossRef] [PubMed]
 
Stockwell-Morris, L, Schulz, RM Medication compliance: the patient’s perspective.Clin Ther1993;15,593-606. [PubMed]
 
Mathew, JP, Parks, R, Savino, JS, et al Atrial fibrillation following coronary artery bypass graft surgery: predictors, outcomes, and resource utilization.JAMA1996;276,300-306. [CrossRef] [PubMed]
 
Yousif, H, Davies, G, Oakley, CM Peri-operative supraventricular arrhythmias in coronary bypass surgery.Int J Cardiol1990;26,313-318. [CrossRef] [PubMed]
 
Olshansky, B Management of atrial fibrillation after coronary artery bypass graft.Am J Cardiol1996;78,27-34. [CrossRef] [PubMed]
 
Gold, MR, O’Gara, PT, Buckley, MJ, et al Efficacy and safety of procainamide in preventing arrhythmias after coronary artery bypass surgery.Am J Cardiol1996;78,975-979. [CrossRef] [PubMed]
 
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