- Email: [email protected]
Post-CABG AF: observation begets more observation!
R. A. Archbold, N.P. Curzen / International Journal of Cardiology 82 (2002) 218 – 219
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[12] Page PL, Pym J. Atrial fibrillation following cardiac surgery. Can J Cardiol 1996;12(Suppl A):A40–4. [13] Taylor GJ, Malik SA, Colliver JA et al. Usefulness of atrial fibrillation as a predictor of stroke after isolated coronary artery bypass grafting. Am J Cardiol 1987;60:905–7. [14] Newman MF, Wolman R, Kanchuger M et al. Multicenter preoperative stroke index for patients undergoing coronary artery bypass graft surgery. Circulation 1996;94(Suppl II):74–80. [15] Frost L, Molgaard H, Christiansen EH, Hjortholm K, Paulsen PK, Thomsen PEB. Atrial fibrillation and flutter after coronary artery bypass surgery: Epidemiology, risk factors and preventive trials. Int J Cardiol 1992;36:253–61. [16] Aranki SA, Shaw DP, Adams DH et al. Predictors of atrial fibrillation after coronary artery surgery. Current trends and impact on hospital resources. Circulation 1996;94:390–7. [17] Mauldin PD, Weintraub WS, Becker ER. Predicting hospital costs for the first-time coronary artery bypass grafting from preoperative and postoperative variables. Am J Cardiol 1994;74:772–5. [18] Carroll RJ, Horn SD, Soderfeldt B, James BC, Malmberg L. International comparison of waiting times for selected cardiovascular procedures. J Am Coll Cardiol 1995;25:557–63. [19] OASIS (Organization to assess strategies for ischaemic syndromes) Registry Investigators, Yusuf S, Flather M, Pogue J et al. Variations between countries in invasive cardiac procedures and outcomes in patients with suspected unstable angina or myocardial infarction without initial ST elevation. Lancet 1998;352:507–14. [20] Batchelor WB, Peterson ED, Mark DB et al. A comparison of US and Canadian cardiac catheterization practices in detecting severe coronary artery disease after myocardial infarction: efficiency, yield and long-term implications. J Am Coll Cardiol 1999;34:12–9. [21] Organisation for Economic Co-operation and Development (OECD) Health Data 1997. [22] Rosenbaum PR, Rubin DB. Reducing bias in observational studies using subclassification on the propensity score. J Am Stat Assoc 1984;79(387):516–23.
[23] Rosenbaum PR, Rubin DB. The central role of the propensity score in observational studies for causal effects. Biomerika 1983;70(1):41–55. [24] Joffe MM, Rosenbaum PR. Invited commentary: propensity scores. Am J Epid 1999;150(4):327–33. [25] Robins JM, Mark SD, Newey WK. Estimating exposure effects by modeling the expectation of exposure conditional in confounders. Biometrics 1992;48:479–95. [26] Cochran WG. The effectiveness of adjustment by subclassification in removing bias in observational studies. Biometrics 1968;24:295– 313. ¨ P, Nilsson L, Stridsberg M, Hansell P, [27] Jidenius L, Blomstrom ¨ Blomstrom-Lundqvist C. Tachyarrythmias and triggering factors after coronary bypass operations. Ann Thorac Surg 2000;69:1064–9. [28] Hannes W, Fasol R, Zajonc H et al. Diltiazem provides anti-ischemic and anti-arrhythmic protection in patients undergoing coronary bypass surgery. Eur J Cardio-Thorac Surg 1993;5:239–45. [29] Seitelberger R, Waltraud H, Gleichauf M, Christoph M, Fasol R. Effects of diltiazem on perioperative ischemia, arrhythmias, and myocardial function in patients undergoing elective coronary grafting. J Thorac Cardiovasc Surg 1994;107:811–21. [30] Tisdale JE, Padhi ID, Goldberg AD et al. A randomized, doubleblind comparison of intravenous diltiazem and digoxin for atrial fibrillation after coronary bypass surgery. Am Heart J 1998;135:739–47. [31] Mooss A, Wurdeman R, Mohiuddin SM et al. Esmolol versus diltiazem in treatment of postoperative atrial fibrillation / atrial flutter after open heart surgery. Am Heart J 2000;140:176–80. [32] Almassi GH, Sommers T, Moritz TE et al. Stroke in cardiac surgical patients: determinants and outcome. Ann Thorac Surg 1999;68:391– 8.
Editorial Comment
Post-CABG AF: observation begets more observation! a, b R. Andrew Archbold *, Nicholas P. Curzen a
Department of Cardiology, St Bartholomew’ s Hospital, Dominion House, 60 Bartholomew Close, West Smithfield, London EC1 A 7 BE, UK b Manchester Heart Centre, Manchester Royal Infirmary, Manchester, UK Received 10 November 2001; accepted 30 November 2001
Atrial fibrillation (AF) occurs in 20–40% of patients after coronary artery bypass graft surgery *Corresponding author. Tel.: 144-207-601-8289; fax: 144-207-6017642. E-mail address: [email protected] (R. Andrew Archbold).
(CABG). It is associated with adverse clinical outcomes and prolongation of hospital stay, resulting in increased resource utilisation and expenditure [1]. Its incidence remains stubbornly unchanged despite advances in clinical practice and much research [2]. In
0167-5273 / 02 / $ – see front matter 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S0167-5273( 01 )00623-4
R. A. Archbold, N.P. Curzen / International Journal of Cardiology 82 (2002) 218 – 219
this issue of The Journal, Majahalme et al. sought to compare the incidence of, and treatment strategies for, AF after CABG in different healthcare systems. They studied patients undergoing first, isolated CABG in one cardiac centre in Finland (public taxfunded), and one in the United States (funded by private insurance). The paper illustrates the pros and cons associated with such observational data. Whilst the authors identify some features of interest, their work raises an important question concerning the ability to interpret observational and comparative data such as these. The basic comparison between the two groups demonstrated a higher incidence of postCABG AF in the Finnish group than the US cohort. This was the case despite several factors that would predict that the incidence would be higher in the American patients. Firstly, the US cohort were higher risk patients with a more acute presentation. Secondly, there was a higher peri-operative use of betablocker therapy, effective protective agents against post-CABG AF [3,4], in the Finnish population. Thirdly, post-operative recovery was more often complicated in the US patients. So what is the reason for this discrepancy between the observed and the expected? The observational design of the study almost certainly provides the explanation. The US data were collected retrospectively and these data are therefore likely to be an underestimate of the incidence of post-CABG AF. The monitoring for AF was not necessarily the same in the two study populations. It is well established in this area of interest that the occurrence of post-operative AF has to be prospectively defined by strict guidelines for both monitoring and reporting the arrhythmia. Even small differences in these factors between the two groups could lead to discrepant data. Is it possible, for example, that in the privately-funded US healthcare system, patients were transferred more rapidly to private and less strictly monitored beds? Nevertheless, the paper raises some interesting questions. Although, the finding that age was independently associated with the development of postCABG AF was expected [2,5], the use of radial artery grafts has not previously been identified as a risk factor for the arrhythmia and its proarrhythmic potential requires confirmation by other studies.
219
Potential mechanisms might include technical aspects of surgery using smaller conduits compared with vein grafts, or arterial graft spasm. Radial artery grafts were employed in 29% of American patients and 1% of Finnish patients, however, so could account for only a minority of the cases of AF. Secondly, it is interesting to note how different the typical treatment response to AF was in the study, with non-elective DC cardioversion performed more frequently in the Finnish patients and amiodarone continued for 30 days used more commonly in the US patients. In common with all observational studies, especially those comparing two groups, data must be treated as thought-provoking and question-stimulating rather than question-answering. It is well established that post-CABG AF is multifactorial in its aetiology, with factors such as sympathetic activation and atrial ectopy in the early post-operative period increasing patients’ inherent susceptibility to arrhythmia [5–7]. To what extent the population differences that have been observed in this study can be attributed to the two healthcare systems specifically will remain speculation. In the field of post-operative AF, observation begets more observation!
References [1] Archbold RA, Curzen N. Atrial fibrillation after coronary artery bypass graft surgery: more than an irritation!. Clin Intensive Care 1999;10:109–16. [2] Cresswell LL, Schuessler RB, Rosenbloom M, Cox JL. Hazards of post-operative atrial arrhythmias. Ann Thorac Surg 1993;56:539–49. [3] Andrews TC, Reimold SC, Berlin JA, Antman EM. Prevention of supraventricular arrhythmias after coronary artery bypass surgery: a meta-analysis of randomized control trials. Circulation 1991;84(Suppl. III):III236–44. [4] Kowey PR, Taylor JE, Rials SJ, Marinchak RA. Meta-analysis of the effectiveness of prophylactic drug therapy in preventing supraventricular arrhythmia early after coronary artery bypass grafting. Am J Cardiol 1992;69:963–5. [5] Zaman AG, Archbold RA, Helft G, Paul EA, Curzen NP, Mills PG. Atrial fibrillation after coronary artery bypass surgery: a model for pre-operative risk stratification. Circulation 2000;101:1403–8. [6] Kalman JM, Munawar M, Howes LG et al. Atrial fibrillation after coronary artery bypass grafting is associated with sympathetic activation. Ann Thorac Surg 1995;60:1709–15. [7] Dimmer C, Tavernier R, Gjorgov N, Van Nooten G, Clement DL, Jordaens L. Variations in autonomic tone preceding onset of atrial fibrillation after coronary artery bypass grafting. Am J Cardiol 1998;82:22–5.
218
[12] Page PL, Pym J. Atrial fibrillation following cardiac surgery. Can J Cardiol 1996;12(Suppl A):A40–4. [13] Taylor GJ, Malik SA, Colliver JA et al. Usefulness of atrial fibrillation as a predictor of stroke after isolated coronary artery bypass grafting. Am J Cardiol 1987;60:905–7. [14] Newman MF, Wolman R, Kanchuger M et al. Multicenter preoperative stroke index for patients undergoing coronary artery bypass graft surgery. Circulation 1996;94(Suppl II):74–80. [15] Frost L, Molgaard H, Christiansen EH, Hjortholm K, Paulsen PK, Thomsen PEB. Atrial fibrillation and flutter after coronary artery bypass surgery: Epidemiology, risk factors and preventive trials. Int J Cardiol 1992;36:253–61. [16] Aranki SA, Shaw DP, Adams DH et al. Predictors of atrial fibrillation after coronary artery surgery. Current trends and impact on hospital resources. Circulation 1996;94:390–7. [17] Mauldin PD, Weintraub WS, Becker ER. Predicting hospital costs for the first-time coronary artery bypass grafting from preoperative and postoperative variables. Am J Cardiol 1994;74:772–5. [18] Carroll RJ, Horn SD, Soderfeldt B, James BC, Malmberg L. International comparison of waiting times for selected cardiovascular procedures. J Am Coll Cardiol 1995;25:557–63. [19] OASIS (Organization to assess strategies for ischaemic syndromes) Registry Investigators, Yusuf S, Flather M, Pogue J et al. Variations between countries in invasive cardiac procedures and outcomes in patients with suspected unstable angina or myocardial infarction without initial ST elevation. Lancet 1998;352:507–14. [20] Batchelor WB, Peterson ED, Mark DB et al. A comparison of US and Canadian cardiac catheterization practices in detecting severe coronary artery disease after myocardial infarction: efficiency, yield and long-term implications. J Am Coll Cardiol 1999;34:12–9. [21] Organisation for Economic Co-operation and Development (OECD) Health Data 1997. [22] Rosenbaum PR, Rubin DB. Reducing bias in observational studies using subclassification on the propensity score. J Am Stat Assoc 1984;79(387):516–23.
[23] Rosenbaum PR, Rubin DB. The central role of the propensity score in observational studies for causal effects. Biomerika 1983;70(1):41–55. [24] Joffe MM, Rosenbaum PR. Invited commentary: propensity scores. Am J Epid 1999;150(4):327–33. [25] Robins JM, Mark SD, Newey WK. Estimating exposure effects by modeling the expectation of exposure conditional in confounders. Biometrics 1992;48:479–95. [26] Cochran WG. The effectiveness of adjustment by subclassification in removing bias in observational studies. Biometrics 1968;24:295– 313. ¨ P, Nilsson L, Stridsberg M, Hansell P, [27] Jidenius L, Blomstrom ¨ Blomstrom-Lundqvist C. Tachyarrythmias and triggering factors after coronary bypass operations. Ann Thorac Surg 2000;69:1064–9. [28] Hannes W, Fasol R, Zajonc H et al. Diltiazem provides anti-ischemic and anti-arrhythmic protection in patients undergoing coronary bypass surgery. Eur J Cardio-Thorac Surg 1993;5:239–45. [29] Seitelberger R, Waltraud H, Gleichauf M, Christoph M, Fasol R. Effects of diltiazem on perioperative ischemia, arrhythmias, and myocardial function in patients undergoing elective coronary grafting. J Thorac Cardiovasc Surg 1994;107:811–21. [30] Tisdale JE, Padhi ID, Goldberg AD et al. A randomized, doubleblind comparison of intravenous diltiazem and digoxin for atrial fibrillation after coronary bypass surgery. Am Heart J 1998;135:739–47. [31] Mooss A, Wurdeman R, Mohiuddin SM et al. Esmolol versus diltiazem in treatment of postoperative atrial fibrillation / atrial flutter after open heart surgery. Am Heart J 2000;140:176–80. [32] Almassi GH, Sommers T, Moritz TE et al. Stroke in cardiac surgical patients: determinants and outcome. Ann Thorac Surg 1999;68:391– 8.
Editorial Comment
Post-CABG AF: observation begets more observation! a, b R. Andrew Archbold *, Nicholas P. Curzen a
Department of Cardiology, St Bartholomew’ s Hospital, Dominion House, 60 Bartholomew Close, West Smithfield, London EC1 A 7 BE, UK b Manchester Heart Centre, Manchester Royal Infirmary, Manchester, UK Received 10 November 2001; accepted 30 November 2001
Atrial fibrillation (AF) occurs in 20–40% of patients after coronary artery bypass graft surgery *Corresponding author. Tel.: 144-207-601-8289; fax: 144-207-6017642. E-mail address: [email protected] (R. Andrew Archbold).
(CABG). It is associated with adverse clinical outcomes and prolongation of hospital stay, resulting in increased resource utilisation and expenditure [1]. Its incidence remains stubbornly unchanged despite advances in clinical practice and much research [2]. In
0167-5273 / 02 / $ – see front matter 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S0167-5273( 01 )00623-4
R. A. Archbold, N.P. Curzen / International Journal of Cardiology 82 (2002) 218 – 219
this issue of The Journal, Majahalme et al. sought to compare the incidence of, and treatment strategies for, AF after CABG in different healthcare systems. They studied patients undergoing first, isolated CABG in one cardiac centre in Finland (public taxfunded), and one in the United States (funded by private insurance). The paper illustrates the pros and cons associated with such observational data. Whilst the authors identify some features of interest, their work raises an important question concerning the ability to interpret observational and comparative data such as these. The basic comparison between the two groups demonstrated a higher incidence of postCABG AF in the Finnish group than the US cohort. This was the case despite several factors that would predict that the incidence would be higher in the American patients. Firstly, the US cohort were higher risk patients with a more acute presentation. Secondly, there was a higher peri-operative use of betablocker therapy, effective protective agents against post-CABG AF [3,4], in the Finnish population. Thirdly, post-operative recovery was more often complicated in the US patients. So what is the reason for this discrepancy between the observed and the expected? The observational design of the study almost certainly provides the explanation. The US data were collected retrospectively and these data are therefore likely to be an underestimate of the incidence of post-CABG AF. The monitoring for AF was not necessarily the same in the two study populations. It is well established in this area of interest that the occurrence of post-operative AF has to be prospectively defined by strict guidelines for both monitoring and reporting the arrhythmia. Even small differences in these factors between the two groups could lead to discrepant data. Is it possible, for example, that in the privately-funded US healthcare system, patients were transferred more rapidly to private and less strictly monitored beds? Nevertheless, the paper raises some interesting questions. Although, the finding that age was independently associated with the development of postCABG AF was expected [2,5], the use of radial artery grafts has not previously been identified as a risk factor for the arrhythmia and its proarrhythmic potential requires confirmation by other studies.
219
Potential mechanisms might include technical aspects of surgery using smaller conduits compared with vein grafts, or arterial graft spasm. Radial artery grafts were employed in 29% of American patients and 1% of Finnish patients, however, so could account for only a minority of the cases of AF. Secondly, it is interesting to note how different the typical treatment response to AF was in the study, with non-elective DC cardioversion performed more frequently in the Finnish patients and amiodarone continued for 30 days used more commonly in the US patients. In common with all observational studies, especially those comparing two groups, data must be treated as thought-provoking and question-stimulating rather than question-answering. It is well established that post-CABG AF is multifactorial in its aetiology, with factors such as sympathetic activation and atrial ectopy in the early post-operative period increasing patients’ inherent susceptibility to arrhythmia [5–7]. To what extent the population differences that have been observed in this study can be attributed to the two healthcare systems specifically will remain speculation. In the field of post-operative AF, observation begets more observation!
References [1] Archbold RA, Curzen N. Atrial fibrillation after coronary artery bypass graft surgery: more than an irritation!. Clin Intensive Care 1999;10:109–16. [2] Cresswell LL, Schuessler RB, Rosenbloom M, Cox JL. Hazards of post-operative atrial arrhythmias. Ann Thorac Surg 1993;56:539–49. [3] Andrews TC, Reimold SC, Berlin JA, Antman EM. Prevention of supraventricular arrhythmias after coronary artery bypass surgery: a meta-analysis of randomized control trials. Circulation 1991;84(Suppl. III):III236–44. [4] Kowey PR, Taylor JE, Rials SJ, Marinchak RA. Meta-analysis of the effectiveness of prophylactic drug therapy in preventing supraventricular arrhythmia early after coronary artery bypass grafting. Am J Cardiol 1992;69:963–5. [5] Zaman AG, Archbold RA, Helft G, Paul EA, Curzen NP, Mills PG. Atrial fibrillation after coronary artery bypass surgery: a model for pre-operative risk stratification. Circulation 2000;101:1403–8. [6] Kalman JM, Munawar M, Howes LG et al. Atrial fibrillation after coronary artery bypass grafting is associated with sympathetic activation. Ann Thorac Surg 1995;60:1709–15. [7] Dimmer C, Tavernier R, Gjorgov N, Van Nooten G, Clement DL, Jordaens L. Variations in autonomic tone preceding onset of atrial fibrillation after coronary artery bypass grafting. Am J Cardiol 1998;82:22–5.