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Atrial fibrillation and flutter after open heart operation
CORRESPONDENCE
Response of Internal Mammary Artery to Sympathomimetic Agents To the Editor: I read with interest the recent letter by van Son and associates [l] on pharmacological response of internal mammary artery (IMA) and gastroepiploic artery. In their letter, they emphasized the differences between IMA and gastroepiploic artery in pharmacological responses to vasoactive agents. They have found that up to approximately 3 to 4 cm proximal to the epigastric bifurcation, the IMA is completely elastic, whereas its first 5 cm as well as the last section is elastomuscular. From these observations, von Son and associates hypothesized that the vasospasm of the IMA may be significantly more apparent in the elastomuscular sections of the IMA and its continuation into the muscular superior epigastric artery and musculophrenic artery. I agree with their opinion because it is in accord with our clinical and experimental findings r2, 31. Van Son and associates quoted our report on the functional study of Padrenoceptor function in the IMA [2] and stated “A study by He and colleagues confirms our hypothesis of a limited reactivity of the IMA to sympathomimetic drugs.” I wish to advise that there may be some misunderstanding on this topic. In our study, we found that Padrenoceptor agonists only induced a weak relaxation in the human IMA, ie, the Padrenoceptor function is weak in this artery. However, this should not be misunderstood as if the IMA responded to sympathomimetic drugs poorly. Sympathomimetic agents include a-adrenoceptor agonists (phenylephrine, methoxamine), Padrenoceptor agonists (isoproterenol), and a- plus Pagonists (epinephrine, norepinephrine). In large arteries, a-adrenoceptorsmediate contraction whereas Padrenoceptor mediate relaxation [4]. Our findings on Padrenoceptors in the IMA suggest that in this artery functional Padrenoceptors are sparse. This does not imply that the a-adrenoceptors are sparse as well. In contrast, we have focused on studies of the contraction in the IMA [2, 3,5] and we found that the human IMA contracted strongly to the thromboxane A, mimetic U46619 and a-adrenoceptor agonists (phenylephrine and norepinephrine) [3]. We suggested that these constrictors may be possible spasmogens for the IMA.Others have obtained similar results [6]. In addition, our further study on a-adrenoceptors in the IMA will be published soon. Therefore, one cannot conclude that the reactivity of the IMA to sympathomimetic drugs is limited. I believe that the distal portion of the human IMA (at the level below the fifth rib and proximal to the bifurcation where the segments of the IMA studied in our experiments were taken from) is pharmacologically active to vasoactive agents and is a place where spasm could occur in response to thromboxane A, or sympathomimetic agents (aadrenoceptor agonists). Guo-Wei He, M D , PhD Cardiovascular Research Hospital For Sick Children 555 UniversifyAve Toronto, Ont Canada MSG 1x8
References 1. Van Son JAM, Smedts F. Pharmacological response of internal mammary artery and gastroepiploic artery. Ann Thorac Surg 1991;51:864. 2. He G-W, Buxton B, Rosenfeldt F, Wilson AC, Angus JA. Weak 0 1992 by The Society of Thoracic Surgeons
3.
4.
5.
6.
Padrenoceptor-mediated relaxation in the human internal mammary artery. J Thorac Cardiovasc Surg 1989;97259-66. He G-W, Buxton 8, Rosenfeldt F, Angus JA. Reactivity of human isolated internal mammary artery to constrictor and dilator agents. Implications for treatment of internal mammary artery spasm. Circulation 1989;8O(Suppl 1):1141-50. Timmermans PBMWM. a-Adrenoceptors. In: Williams M, Glennon RA, Timmermans PBMWM, ed. Receptor pharmacology and function. 1st ed. New York: Marcel Dekker, 1989:17>205. He G-W, Angus JA, Rosenfeldt FL. Reactivity of the canine isolated internal mammary artery, saphenous vein, and coronary artery to constrictor and dilator substances: relevance to coronary bypass graft surgery. J Cardiovasc Pharmacol 1988; 1212-22. Weinstein JS, Grossman W, Weintraub Rh4, Thurer RL, Johnson RG, Morgan KG. Differences in a-adrenergic responsiveness between human internal mammary arteries and saphenous veins. Circulation 1989;79:12&70.
Atrial Fibrillation and Flutter After Open Heart Operation To the Editor: We read with interest the article by Fanning and associates [l] concerning prophylaxis of supraventricular tachyarrhythmias with magnesium sulfate after coronary artery bypass grafting. In this letter we present our experience with atrial fibrillation and flutter, with special regard to predictors and to prophylactic postoperative digitalization. An outline of treatment is also briefly provided. A total of 1,530 consecutive patients undergoing cardiac operation and treated postoperatively with digitalis to prevent supraventricular tachyarrhythmias were observed to evaluate the onset of sustained atrial fibrillation and flutter. They were 1,082 male (average age, 56.9 years) and 448 female patients (average age, 52.6 years). Patients with previous supraventricular arrhythmias, high-degree atrioventricular block, proved sensitivity to digoxin, and renal failure (creatinine clearance < 70 mumin) were excluded from the study. Administration of amiodarone, Pblockers and digitalis, if done, was suspended 7,2, and 1 days respectively, before operation. Sixty-four percent (979 patients) underwent myocardial revascularization; 23.1% (353 patients), valvular operation; 7.7% (118 patients), radical correction of congenital cardiopathies; and 5.2% (80 patients), various associated procedures. All patients were given 0.4 mg of digitalis (Cedilanid; Sandoz, Milan, Italy) intravenously within 2 hours postoperatively, and the dose was repeated after 12 hours. An additional 0.4 mg was given in two separate doses intravenously on the first and second postoperative days, and 0.25 mg was given by mouth each day for the next 7 days. All patients underwent continuous electrocardiographic monitoring for 48 hours; standard 12-lead electrocardiograms were obtained daily for 3 days postoperatively and on the day before recovery. After transfer from the intensive care unit and suspension of continuous monitoring, cardiograms and rhythm stripes were obtained whenever the pulse became irregular or was recorded to be outside the range of 50 to 130 beatdmin. We also performed an extensive analysis of 24 variables: 8 preoperative (age, sex, hypertension, diabetes, smoking, left atrial dilatation, ejection fraction, drugs); 4 intraoperative (aortic cross-clamp time, cardioplegia, incomplete coronary revascularization, ventricular defibrillation); and 12 postoperative (shock, myocardial infarction, stroke, central venous pressure, inspired oxygen fraction, potassium level, free triiodothyroninelevel, free thyroxAnn Thorac Surg 1992;53:94&5
0003-4975/92/$5.00
Ann Thorac Surg 1992;5394&5
h e level, anemia, infection, drugs, mediastinal drainage). For reversion to sinus rhythm amiodarone or verapamil was used indifferently. The mean overall incidence of sustained atrial fibrillation and flutter was 12.1% (ranging from 5.9% in congenital correction to 21.7% in associated procedures); the incidence was only 7.8% in myocardial revascularization. Incidence of arrhythmias was greater within the first 48 postoperative hours (54.1%of patients) and in patients aged 60 years and over (58.3% of patients). Reversion to sinus rhythm was obtained with amiodarone in 144 patients (previous treatment with verapamil was ineffective in 29 patients), with verapamil in 22 patients, and with late directcurrent conversion in 17 patients (3 were receiving amiodarone and 17 were receiving verapamil). In 2 patients arrhythmias persisted at the time of recovery. There was no greater incidence of cardiovascular morbidity or mortality suggesting digitalis toxicity. Atrial fibrillation and flutter are relatively frequent after cardiac operations, ranging from 8% to 100% [2, 31, and age has been suggested as the most important predictor [4, 51. If we consider only sustained atrial fibrillation and flutter occurring after coronary bypass grafting, their incidence ranges from 11.4% to 40% [6]. Discordance exists as to whether digitalization is effective [2] to reduce the incidence of such arrhythmias or not [6]; similarly, many therapeutic regimens aimed at preventing arrhythmias and at establishing and maintaining sinus rhythm have been tested [I, 31. In conclusion our data suggest age only, and none of the other 23 risk factors considered, as predictive of atrial fibrillation and flutter after open heart operations. Patients undergoing associated procedures are at higher risk for development of such arrhythmias, whereas the incidence is only 7.8% in patients undergoing myocardial revascularization. Immediate postoperative digitalization, according to the guidelines proposed, is riskfree, well-tolerated, and effective in prophylaxis of sustained major supraventricular tachyarrhythmias, limiting to only 12.1% the mean overall incidence of atrial fibrillation and flutter. Reversion to sinus rhythm is obtained with both amiodarone and verapamil, even if the first one seems to be more effective.
Edoardo Santoli, M D Daniele G. Di Mattia, M D Roberto Scrofani, M D Department of Thoracic and Cardiovascular Surge y L. Sacco Hospital Via G.B. Grassi, 74 20157 Milan, Italy
References 1. Fanning WJ, Thomas CS Jr, Roach A, et al. Prophylaxis of atrial fibrillation with magnesium sulfate after coronary artery bypass grafting. Ann Thorac Surg 1991;52:52W3. 2. Csicsko JF, Schatzlein MH, King RD. Immediate postoperative digitalization in the prophylaxis of supraventricular arrhythmias following coronary artery bypass. J Thorac Cardiovasc Surg 1981;81:419-22. 3. McAlister HF, Luke RA, Whitlock RM, Smith WM. Intravenous amiodarone bolus versus oral quinidine for atrial flutter and fibrillation after cardiac operations. J Thorac Cardiovasc Surg 1990;99:911-8. 4. Leitch JW, Thomson D, Baird DK, Harris PJ. The importance of age as predictor of atrial fibrillation and flutter after coronary artery bypass grafting. J Thorac Cardiovasc Surg 1990;
100:33%42. 5. Fuller JA, Adams GG, Baxton B. Atrial fibrillation after coro-
CORRESPONDENCE
941
nary artery bypass grafting. J Thorac Cardiovasc Surg 1989;97 821-5. 6. Rubin DA, Nieminski KE, Reed GE, Herman MV. Predictors, prevention, and long-term prognosis of atrial fibrillation after coronary artery bypass graft operations. J Thorac Cardiovasc Surg 1987;94331-5.
Reply
To the Editor:
We thank Drs Santoli, Di Mattia and Scrofani for their interest in our report. Their letter supports previously published data suggesting that atrial fibrillation after cardiac operations is more common in the elderly [l]. Given the observational nature of their report it does not justify the conclusion that postoperative digitalization is effective prophylaxis for supraventricular tachyarrhythmias (SVT) after cardiac operations. The incidence of SVT after cardiac operations seems to vary with the sophistication of the techniques used for their detection. White and associates [2] studied 41 patients undergoing coronary bypass and found by using a 7-day continuous Holter tape recording system that some SVT developed in all patients in the postoperative period, although many episodes were clinically insignificant. Although relatively frequent, postoperative SVT do not seem to adversely affect the perioperative mortality or long-term survival of patients undergoing coronary artery bypass [3]. As such, strategies to prevent the occurrence of SVT in the postoperative period should be relatively benign. Some controlled clinical trials support the use of @blockers (usually propranolol) or digitalis in preventing SVT, whereas other studies refute such claims [4]. Verapamil has also been effective in preventing SVT, but with a high incidence of unacceptable side effects [5]. These conflicting results are related in part to the relatively small size of most studies, variations in the methods of arrhythmia detection, lack of a standardized definition of a "clinically significant" arrhythmia, and most importantly our fundamental ignorance of the pathogenesis of postoperative SVT. Further work on this common problem should be directed not only at prevention but, more importantly, at defining the causes of postoperative SVT. Recent considerations include the disruptive mechanical effects of right atrial cannulation [6], inadequate right atrial myocardial protection [7], diminished myocardial magnesium content [B], and altered atrial preceptor density [4]. A more complete understanding of the pathogenesis of postoperative SVT should facilitate the use of specific perioperative prophylactic measures and thereby replace the current empiric approaches to this problem.
William 1. Fanning, M D Clarence S . Thomas, M D 300 E Town St, 12th Floor Columbus, OH 43215
References Leitch JW, Thomson D, Baird DK, Harris PJ. The importance of age as a predictor of atrial fibrillation and flutter after coronary artery bypass grafting. J Thorac Cardiovasc Surg 1990;100338-42. White HD, Antman EM, Glynn MA, et al. Efficacy and safety of timolol for prevention of supraventricular tachyarrhythmias after coronary artery bypass surgery. Circulation 1984;70: 479-84. Rubin DA, Nieminski KE, Reed GE, Herman MV. Predictors, prevention, and long-term prognosis of atrial fibrillation after
Response of Internal Mammary Artery to Sympathomimetic Agents To the Editor: I read with interest the recent letter by van Son and associates [l] on pharmacological response of internal mammary artery (IMA) and gastroepiploic artery. In their letter, they emphasized the differences between IMA and gastroepiploic artery in pharmacological responses to vasoactive agents. They have found that up to approximately 3 to 4 cm proximal to the epigastric bifurcation, the IMA is completely elastic, whereas its first 5 cm as well as the last section is elastomuscular. From these observations, von Son and associates hypothesized that the vasospasm of the IMA may be significantly more apparent in the elastomuscular sections of the IMA and its continuation into the muscular superior epigastric artery and musculophrenic artery. I agree with their opinion because it is in accord with our clinical and experimental findings r2, 31. Van Son and associates quoted our report on the functional study of Padrenoceptor function in the IMA [2] and stated “A study by He and colleagues confirms our hypothesis of a limited reactivity of the IMA to sympathomimetic drugs.” I wish to advise that there may be some misunderstanding on this topic. In our study, we found that Padrenoceptor agonists only induced a weak relaxation in the human IMA, ie, the Padrenoceptor function is weak in this artery. However, this should not be misunderstood as if the IMA responded to sympathomimetic drugs poorly. Sympathomimetic agents include a-adrenoceptor agonists (phenylephrine, methoxamine), Padrenoceptor agonists (isoproterenol), and a- plus Pagonists (epinephrine, norepinephrine). In large arteries, a-adrenoceptorsmediate contraction whereas Padrenoceptor mediate relaxation [4]. Our findings on Padrenoceptors in the IMA suggest that in this artery functional Padrenoceptors are sparse. This does not imply that the a-adrenoceptors are sparse as well. In contrast, we have focused on studies of the contraction in the IMA [2, 3,5] and we found that the human IMA contracted strongly to the thromboxane A, mimetic U46619 and a-adrenoceptor agonists (phenylephrine and norepinephrine) [3]. We suggested that these constrictors may be possible spasmogens for the IMA.Others have obtained similar results [6]. In addition, our further study on a-adrenoceptors in the IMA will be published soon. Therefore, one cannot conclude that the reactivity of the IMA to sympathomimetic drugs is limited. I believe that the distal portion of the human IMA (at the level below the fifth rib and proximal to the bifurcation where the segments of the IMA studied in our experiments were taken from) is pharmacologically active to vasoactive agents and is a place where spasm could occur in response to thromboxane A, or sympathomimetic agents (aadrenoceptor agonists). Guo-Wei He, M D , PhD Cardiovascular Research Hospital For Sick Children 555 UniversifyAve Toronto, Ont Canada MSG 1x8
References 1. Van Son JAM, Smedts F. Pharmacological response of internal mammary artery and gastroepiploic artery. Ann Thorac Surg 1991;51:864. 2. He G-W, Buxton B, Rosenfeldt F, Wilson AC, Angus JA. Weak 0 1992 by The Society of Thoracic Surgeons
3.
4.
5.
6.
Padrenoceptor-mediated relaxation in the human internal mammary artery. J Thorac Cardiovasc Surg 1989;97259-66. He G-W, Buxton 8, Rosenfeldt F, Angus JA. Reactivity of human isolated internal mammary artery to constrictor and dilator agents. Implications for treatment of internal mammary artery spasm. Circulation 1989;8O(Suppl 1):1141-50. Timmermans PBMWM. a-Adrenoceptors. In: Williams M, Glennon RA, Timmermans PBMWM, ed. Receptor pharmacology and function. 1st ed. New York: Marcel Dekker, 1989:17>205. He G-W, Angus JA, Rosenfeldt FL. Reactivity of the canine isolated internal mammary artery, saphenous vein, and coronary artery to constrictor and dilator substances: relevance to coronary bypass graft surgery. J Cardiovasc Pharmacol 1988; 1212-22. Weinstein JS, Grossman W, Weintraub Rh4, Thurer RL, Johnson RG, Morgan KG. Differences in a-adrenergic responsiveness between human internal mammary arteries and saphenous veins. Circulation 1989;79:12&70.
Atrial Fibrillation and Flutter After Open Heart Operation To the Editor: We read with interest the article by Fanning and associates [l] concerning prophylaxis of supraventricular tachyarrhythmias with magnesium sulfate after coronary artery bypass grafting. In this letter we present our experience with atrial fibrillation and flutter, with special regard to predictors and to prophylactic postoperative digitalization. An outline of treatment is also briefly provided. A total of 1,530 consecutive patients undergoing cardiac operation and treated postoperatively with digitalis to prevent supraventricular tachyarrhythmias were observed to evaluate the onset of sustained atrial fibrillation and flutter. They were 1,082 male (average age, 56.9 years) and 448 female patients (average age, 52.6 years). Patients with previous supraventricular arrhythmias, high-degree atrioventricular block, proved sensitivity to digoxin, and renal failure (creatinine clearance < 70 mumin) were excluded from the study. Administration of amiodarone, Pblockers and digitalis, if done, was suspended 7,2, and 1 days respectively, before operation. Sixty-four percent (979 patients) underwent myocardial revascularization; 23.1% (353 patients), valvular operation; 7.7% (118 patients), radical correction of congenital cardiopathies; and 5.2% (80 patients), various associated procedures. All patients were given 0.4 mg of digitalis (Cedilanid; Sandoz, Milan, Italy) intravenously within 2 hours postoperatively, and the dose was repeated after 12 hours. An additional 0.4 mg was given in two separate doses intravenously on the first and second postoperative days, and 0.25 mg was given by mouth each day for the next 7 days. All patients underwent continuous electrocardiographic monitoring for 48 hours; standard 12-lead electrocardiograms were obtained daily for 3 days postoperatively and on the day before recovery. After transfer from the intensive care unit and suspension of continuous monitoring, cardiograms and rhythm stripes were obtained whenever the pulse became irregular or was recorded to be outside the range of 50 to 130 beatdmin. We also performed an extensive analysis of 24 variables: 8 preoperative (age, sex, hypertension, diabetes, smoking, left atrial dilatation, ejection fraction, drugs); 4 intraoperative (aortic cross-clamp time, cardioplegia, incomplete coronary revascularization, ventricular defibrillation); and 12 postoperative (shock, myocardial infarction, stroke, central venous pressure, inspired oxygen fraction, potassium level, free triiodothyroninelevel, free thyroxAnn Thorac Surg 1992;53:94&5
0003-4975/92/$5.00
Ann Thorac Surg 1992;5394&5
h e level, anemia, infection, drugs, mediastinal drainage). For reversion to sinus rhythm amiodarone or verapamil was used indifferently. The mean overall incidence of sustained atrial fibrillation and flutter was 12.1% (ranging from 5.9% in congenital correction to 21.7% in associated procedures); the incidence was only 7.8% in myocardial revascularization. Incidence of arrhythmias was greater within the first 48 postoperative hours (54.1%of patients) and in patients aged 60 years and over (58.3% of patients). Reversion to sinus rhythm was obtained with amiodarone in 144 patients (previous treatment with verapamil was ineffective in 29 patients), with verapamil in 22 patients, and with late directcurrent conversion in 17 patients (3 were receiving amiodarone and 17 were receiving verapamil). In 2 patients arrhythmias persisted at the time of recovery. There was no greater incidence of cardiovascular morbidity or mortality suggesting digitalis toxicity. Atrial fibrillation and flutter are relatively frequent after cardiac operations, ranging from 8% to 100% [2, 31, and age has been suggested as the most important predictor [4, 51. If we consider only sustained atrial fibrillation and flutter occurring after coronary bypass grafting, their incidence ranges from 11.4% to 40% [6]. Discordance exists as to whether digitalization is effective [2] to reduce the incidence of such arrhythmias or not [6]; similarly, many therapeutic regimens aimed at preventing arrhythmias and at establishing and maintaining sinus rhythm have been tested [I, 31. In conclusion our data suggest age only, and none of the other 23 risk factors considered, as predictive of atrial fibrillation and flutter after open heart operations. Patients undergoing associated procedures are at higher risk for development of such arrhythmias, whereas the incidence is only 7.8% in patients undergoing myocardial revascularization. Immediate postoperative digitalization, according to the guidelines proposed, is riskfree, well-tolerated, and effective in prophylaxis of sustained major supraventricular tachyarrhythmias, limiting to only 12.1% the mean overall incidence of atrial fibrillation and flutter. Reversion to sinus rhythm is obtained with both amiodarone and verapamil, even if the first one seems to be more effective.
Edoardo Santoli, M D Daniele G. Di Mattia, M D Roberto Scrofani, M D Department of Thoracic and Cardiovascular Surge y L. Sacco Hospital Via G.B. Grassi, 74 20157 Milan, Italy
References 1. Fanning WJ, Thomas CS Jr, Roach A, et al. Prophylaxis of atrial fibrillation with magnesium sulfate after coronary artery bypass grafting. Ann Thorac Surg 1991;52:52W3. 2. Csicsko JF, Schatzlein MH, King RD. Immediate postoperative digitalization in the prophylaxis of supraventricular arrhythmias following coronary artery bypass. J Thorac Cardiovasc Surg 1981;81:419-22. 3. McAlister HF, Luke RA, Whitlock RM, Smith WM. Intravenous amiodarone bolus versus oral quinidine for atrial flutter and fibrillation after cardiac operations. J Thorac Cardiovasc Surg 1990;99:911-8. 4. Leitch JW, Thomson D, Baird DK, Harris PJ. The importance of age as predictor of atrial fibrillation and flutter after coronary artery bypass grafting. J Thorac Cardiovasc Surg 1990;
100:33%42. 5. Fuller JA, Adams GG, Baxton B. Atrial fibrillation after coro-
CORRESPONDENCE
941
nary artery bypass grafting. J Thorac Cardiovasc Surg 1989;97 821-5. 6. Rubin DA, Nieminski KE, Reed GE, Herman MV. Predictors, prevention, and long-term prognosis of atrial fibrillation after coronary artery bypass graft operations. J Thorac Cardiovasc Surg 1987;94331-5.
Reply
To the Editor:
We thank Drs Santoli, Di Mattia and Scrofani for their interest in our report. Their letter supports previously published data suggesting that atrial fibrillation after cardiac operations is more common in the elderly [l]. Given the observational nature of their report it does not justify the conclusion that postoperative digitalization is effective prophylaxis for supraventricular tachyarrhythmias (SVT) after cardiac operations. The incidence of SVT after cardiac operations seems to vary with the sophistication of the techniques used for their detection. White and associates [2] studied 41 patients undergoing coronary bypass and found by using a 7-day continuous Holter tape recording system that some SVT developed in all patients in the postoperative period, although many episodes were clinically insignificant. Although relatively frequent, postoperative SVT do not seem to adversely affect the perioperative mortality or long-term survival of patients undergoing coronary artery bypass [3]. As such, strategies to prevent the occurrence of SVT in the postoperative period should be relatively benign. Some controlled clinical trials support the use of @blockers (usually propranolol) or digitalis in preventing SVT, whereas other studies refute such claims [4]. Verapamil has also been effective in preventing SVT, but with a high incidence of unacceptable side effects [5]. These conflicting results are related in part to the relatively small size of most studies, variations in the methods of arrhythmia detection, lack of a standardized definition of a "clinically significant" arrhythmia, and most importantly our fundamental ignorance of the pathogenesis of postoperative SVT. Further work on this common problem should be directed not only at prevention but, more importantly, at defining the causes of postoperative SVT. Recent considerations include the disruptive mechanical effects of right atrial cannulation [6], inadequate right atrial myocardial protection [7], diminished myocardial magnesium content [B], and altered atrial preceptor density [4]. A more complete understanding of the pathogenesis of postoperative SVT should facilitate the use of specific perioperative prophylactic measures and thereby replace the current empiric approaches to this problem.
William 1. Fanning, M D Clarence S . Thomas, M D 300 E Town St, 12th Floor Columbus, OH 43215
References Leitch JW, Thomson D, Baird DK, Harris PJ. The importance of age as a predictor of atrial fibrillation and flutter after coronary artery bypass grafting. J Thorac Cardiovasc Surg 1990;100338-42. White HD, Antman EM, Glynn MA, et al. Efficacy and safety of timolol for prevention of supraventricular tachyarrhythmias after coronary artery bypass surgery. Circulation 1984;70: 479-84. Rubin DA, Nieminski KE, Reed GE, Herman MV. Predictors, prevention, and long-term prognosis of atrial fibrillation after