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Effect of body mass index on defibrillation thresholds for internal cardioversion in patients with atrial fibrillation
Effect of Body Mass Index on Defibrillation Thresholds for Internal Cardioversion in Patients With Atrial Fibrillation Peter M. Kistler, MBBS, Prashanthan Sanders, MBBS, PhD, Joseph B. Morton, MBBS, PhD, Jitendra K. Vohra, MD, Jonathan M. Kalman, MBBS, PhD, and Paul B. Sparks, MBBS, PhD This study reports that patients with large body mass indexes (BMIs) and long-duration atrial fibrillation (AF) have greater defibrillation thresholds than patients with normal BMIs and AF of short duration. BMI is an independent predictor of defibrillation thresholds in patients with longer duration AF in whom external cardioversion has failed. 䊚2004 by Excerpta Medica, Inc. (Am J Cardiol 2004;94:370 –372)
e sought to determine (1) whether body mass index (BMI) had any effect on defibrillation W thresholds and (2) whether the cardioversion of longer duration atrial fibrillation (AF) was associated with greater defibrillation thresholds compared with AF of very short duration. •••
Twenty-four patients underwent low-energy internal cardioversion for AF. All patients gave written informed consent. The study was approved by the Royal Melbourne Hospital Research and Ethics Committee. There were 2 groups of patients. Patients were considered for internal cardioversion if they were symptomatic, if 2 previous attempts of external cardioversion had failed using biphasic shock waveforms at 360 J maximum delivered energy with the paddles in the anteroposterior position, or if they required cardioversion as part of a pulmonary vein isolation procedure for treatment of paroxysmal AF. Chronic AF was defined as AF lasting ⬎3 months. Paroxysmal AF was defined as AF lasting ⬍7 days separated by periods of sinus rhythm. Internal cardioversion was performed under general anesthesia. Transesophageal echocardiography was performed before shock delivery to exclude left atrial thrombus and to assess left atrial mechanical function. A 7Fr cardioversion catheter (the Response CV, St. Jude Medical, St. Paul, Minnesota) was introduced through a 7Fr lockable sheath inserted into the right internal jugular vein. The catheter has a proximal coil (anode) that was positioned at the right atrium– From the Department Of Cardiology, Royal Melbourne Hospital, Melbourne; and the Department of Medicine, University of Melbourne, Melbourne, Australia. Drs. Kistler and Sanders are recipients of Medical Postgraduate Research Scholarships from the National Health and Medical Research Council of Australia, Austrailia. Dr. Sparks is a recipient of a National Heart Foundation Grant and the Sylvia Charles Viertel Scholarship. Dr. Sparks’ address is: Department of Cardiology, Royal Melbourne Hospital, Melbourne, Australia 3050. E-mail: [email protected]. Manuscript received January 13, 2004; revised manuscript received and accepted April 13, 2004.
370
©2004 by Excerpta Medica, Inc. All rights reserved. The American Journal of Cardiology Vol. 94 August 1, 2004
superior vena cava junction and a 10-pole (2-8-2 spacing cathode) placed into the coronary sinus. The position was confirmed with venography because the cardioversion catheter has a lumen that facilitates contrast injection (Figure 1). A standard 6Fr quadripolar catheter was introduced through the right femoral vein and positioned at the right ventricular apex for R-wave synchronization. Internal cardioversion was performed using a step-up protocol of energy output starting at 2 J, then 5 J, and increased in 5-J increments up to a maximum of 50 J or until sinus rhythm was achieved. Successful cardioversion was defined, as in a previous series, as the restoration of sinus rhythm lasting ⬎1 minute.1 Patients with chronic AF were anticoagulated to a target international normalized ratio of 2 to 3 for 4 weeks before cardioversion. Anticoagulation was discontinued 5 days before the day of planned cardioversion. Enoxaparin 1 mg/kg/day was subcutaneously administered once the international normalized ratio was ⬍2 until the day before the procedure. After successful cardioversion, unfractionated heparin was commenced. The following day, enoxaparin replaced unfractionated heparin and was continued until the international normalized ratio stabilized at ⬎2. The duration of the subsequent anticoagulation was ⱖ4 weeks. Patients who underwent pulmonary vein isolation were not cardioverted until transseptal access had been obtained. After access to the left atrium, intravenous heparin was commenced, and an activated clotting time of ⬎250 ms was maintained throughout the procedure. It was only during adequate anticoagulation that cardioversion was performed. Postoperative anticoagulation then proceeded as previously described. All variables are expressed as mean ⫾ SE. Statistical comparisons between groups were made using the 2-tailed Student’s t test for unpaired data or the Mann-Whitney rank sum test when a normal distribution could not be assumed. Linear regression analysis was used to assess the relation between BMI and energy requirements. Regression coefficients () are expressed with 95% confidence intervals. A p value ⬍0.05 was considered statistically significant. Patient demographics are listed in Table 1. The patients in the failed external cardioversion group weighed significantly more (119 ⫾ 8 kg vs 87 ⫾ 5 kg; p ⬍0.01). They also had a BMI of 36 ⫾ 2, compared with 28 ⫾ 1 (p ⫽ 0.01) in the pulmonary vein isolation group. The duration of AF and left atrial dimensions also varied between the 2 patient groups. 0002-9149/04/$–see front matter doi:10.1016/j.amjcard.2004.04.039
•••
In the present study, we have demonstrated that defibrillation thresholds are increased in patients with chronic AF with high BMIs compared with those with paroxysmal AF and lower BMIs. The number of shocks required to achieve cardioversion was significantly increased in the population with chronic AF and high BMIs in comparison with the patients with paroxysmal AF and lower BMIs. Within the patient population with chronic AF, BMI was found to be predictive of defibrillation thresholds, independent of AF duration. The new single cardioverFIGURE 1. The cardioversion catheter in the coronary sinus is confirmed on venograsion catheter used in this study, phy in a case of failed external cardioversion. The proximal coil lies in the lateral which allowed electrophysiologic reright atrium (RA) and the distal coil in the coronary sinus (CS). A standard quadripocording and coronary sinus venogralar catheter is positioned at the right ventricle (RV) apex for R-wave synchronization. phy, was successful in all cases and LAO ⴝ left anterior oblique; RAO ⴝ right anterior oblique. was used without complications. The duration of AF has been established as an important determinant of the energy required for sucTABLE 1 Baseline Characteristics cessful cardioversion.2,3 In keeping Failed External Pulmonary Vein with our findings, earlier studies by Cardioversion Isolation Levy et al2 found that significantly Variable (n ⫽ 13) (n ⫽ 11) p Value greater energy was required for sucAge (yrs) 56.3 ⫾ 2.4 50.3 ⫾ 3.0 NS cessful cardioversion in the chronic Men/women 12/1 8/3 group compared with those in the Weight (kg) 119 ⫾ 8 87 ⫾ 5 ⬍0.01 paroxysmal AF group. Weight rather 36 ⫾ 2 28 ⫾ 1 0.01 BMI (kg/m2) than BMI was examined in this study Duration of AF episode 21 ⫾ 12 mo 31 ⫾ 7 h ⬍0.01 Left atrial size (mm) 50 ⫾ 2 39 ⫾ 3 0.01 and found not to be predictive. PaStructural heart disease 6 3 NS tients who had repeat internal carFailed antiarrhythmic drugs 0.8 ⫾ 0.1 1.5 ⫾ 0.3 0.01 dioversion had significantly lower defibrillation thresholds at the time of second cardioversion, which correlated with a shorter duration of All patients underwent successful cardioversion. AF before the second cardioversion.4 In the present The failed external cardioversion group required a study, the patients in the failed external cardioversion significantly greater mean energy of 15 ⫾ 1 J, com- group were in chronic AF for a median duration of pared with 8 ⫾ 0.1 J in the pulmonary vein isolation 20 months compared with patients in the paroxysmal group (Figure 2; p ⬍0.001). The failed external car- group, in whom the mean duration of AF episodes dioversion group also required a greater number of was 31 hours. Of particular interest was a marked shocks to achieve success (3.8 ⫾ 0.2 vs 2.7 ⫾ 0.2 difference in BMI between the 2 groups. Because of shocks in the pulmonary vein isolation group; p ⫽ the inherent differences between the 2 groups, we also 0.003). This is by virtue of the step-up protocol. examined the group of patients in whom external Linear regression analysis showed that there was a cardioversion failed. We found that an increase in significant association between BMI and energy redefibrilquired for successful cardioversion ( ⫽ 0.31 [0.01 to BMI correlated significantly with increasing 5 recently relation thresholds. Sharp and Whalley 0.61], p ⫽ 0.047) (Figure 3). The effect of BMI was independent of the duration of arrhythmia (likelihood ported 100% success with a dual-catheter approach with a defibrillation threshold of 12.1 J in those with ratio test: chi-square 1.02, p ⫽ 0.313). The cardioversion catheter was successfully posi- a BMI of 29 in whom external cardioversion failed. tioned in the coronary sinus in all 24 patients. There However, correlation between BMI and defibrillawas no need for a dual-catheter approach or alterna- tion threshold was not performed in this study. The tive positions for internal cardioversion. There were relation between BMI and defibrillation threshold no complications. In particular, there were no ventric- has been previously reported in external cardioverular arrhythmias or failures of synchronization. There sion6 and from the present study appears to be a were also no access hematomas or thromboembolic predictor in internal cardioversion. Obesity is associcomplications. ated with left ventricular hypertrophy and diastolic BRIEF REPORTS
371
further possibility is that of increased cardiac fat around and investing the coronary sinus, which could result in increased impedance and energy requirements. An appreciation of an expected greater defibrillation threshold in patients with larger BMIs could lead to a reduction in the number of shocks. This is particularly relevant for patient comfort when performing internal cardioversion under no or minimal sedation.8 It is our practice to perform internal cardioversion under general anesthesia because of interindividual variability in pain 9 and defibrillation thresholds. In external cardioversion, it has been shown that starting at a greater energy in patients with persistent AF reduces the number of shocks delivered.10
FIGURE 2. The group of patients who had failed external cardioversion (EXT CV) had significantly higher defibrillation thresholds and BMIs compared with the group of patients who had pulmonary vein isolation (PVI).
Acknowledgment: We would like to thank Dr. Lachlan Macgregor from the Department of Biostatistics for his assistance with the statistical analysis.
1. Andraghetti A, Scalese M. Safety and efficacy of
low-energy cardioversion of 500 patients using two different techniques. Europace 2001;3:4 –9. 2. Levy S, Ricard P, Gueunoun M, Yapo F, Trigano J, Mansouri C, Paganelli F. Low-energy cardioversion of spontaneous atrial fibrillation. Immediate and long-term results. Circulation 1997;96:253– 259. 3. Boriani G, Biffi M, Camanini C, Bacchi L, Zannoli R, Luceri R, Branzi A. Predictors of atrial defibrillation threshold in internal cardioversion. Pacing Clin Electrophysiol 2000;23:1898 –1901. 4. Ammer R, Lehmann G, Plewan A, Puetter K, Alt E. Marked reduction in atrial defibrillation thresholds with repeated internal cardioversion. J Am Coll Cardiol 1999;34:1569 –1576. 5. Sharp JC, Whalley DW. Effectiveness and safety of low-energy internal cardioversion of long-standing atrial fibrillation after unsuccessful external cardioversion. Am J Cardiol 2002;90:657–660. 6. Kerber RE. Transthoracic cardioversion of atrial fibrillation and flutter: standard techniques and new advances. Am J Cardiol 1996;78:22–26. 7. Alpert MA, Hashimi MW. Obesity and the heart. Am J Med Sci 1993;306:117–123. 8. Boriani G, Biffi M, Camanini C, Luceri RM, Branzi A. Transvenous low energy internal cardioFIGURE 3. BMI showed a significant correlation with defibrillation threshold (DFT) in the version for atrial fibrillation: a review of clinical group of patients with chronic AF. applications and future developments. Pacing Clin Electrophysiol 2001;24:99 –107. 9. Santini M, Pandozi C, Altamura G, Gentilucci G, Villani M, Scianaro MC, Castro A, Ammirati dysfunction,7 with the potential consequences of in- F, Magris B. Single shock endocavitary low energy intracardiac cardioversion chronic atrial fibrillation. J Interv Card Electrophysiol 1999;3:45–51. creased left atrial pressure and size. Although specu- of 10. Boos C, Thomas M, Jones A, Clarke E, Wilbourne G, More R. Higher energy lative, these atrial effects may result in elevated defi- monophasic DC cardioversion for persistent atrial fibrillation: is it time to start at brillation thresholds in patients with elevated BMIs. A 360 joules? Ann Noninvasive Electrocardiol 2003;8:121–126.
372 THE AMERICAN JOURNAL OF CARDIOLOGY姞
VOL. 94
AUGUST 1, 2004
e sought to determine (1) whether body mass index (BMI) had any effect on defibrillation W thresholds and (2) whether the cardioversion of longer duration atrial fibrillation (AF) was associated with greater defibrillation thresholds compared with AF of very short duration. •••
Twenty-four patients underwent low-energy internal cardioversion for AF. All patients gave written informed consent. The study was approved by the Royal Melbourne Hospital Research and Ethics Committee. There were 2 groups of patients. Patients were considered for internal cardioversion if they were symptomatic, if 2 previous attempts of external cardioversion had failed using biphasic shock waveforms at 360 J maximum delivered energy with the paddles in the anteroposterior position, or if they required cardioversion as part of a pulmonary vein isolation procedure for treatment of paroxysmal AF. Chronic AF was defined as AF lasting ⬎3 months. Paroxysmal AF was defined as AF lasting ⬍7 days separated by periods of sinus rhythm. Internal cardioversion was performed under general anesthesia. Transesophageal echocardiography was performed before shock delivery to exclude left atrial thrombus and to assess left atrial mechanical function. A 7Fr cardioversion catheter (the Response CV, St. Jude Medical, St. Paul, Minnesota) was introduced through a 7Fr lockable sheath inserted into the right internal jugular vein. The catheter has a proximal coil (anode) that was positioned at the right atrium– From the Department Of Cardiology, Royal Melbourne Hospital, Melbourne; and the Department of Medicine, University of Melbourne, Melbourne, Australia. Drs. Kistler and Sanders are recipients of Medical Postgraduate Research Scholarships from the National Health and Medical Research Council of Australia, Austrailia. Dr. Sparks is a recipient of a National Heart Foundation Grant and the Sylvia Charles Viertel Scholarship. Dr. Sparks’ address is: Department of Cardiology, Royal Melbourne Hospital, Melbourne, Australia 3050. E-mail: [email protected]. Manuscript received January 13, 2004; revised manuscript received and accepted April 13, 2004.
370
©2004 by Excerpta Medica, Inc. All rights reserved. The American Journal of Cardiology Vol. 94 August 1, 2004
superior vena cava junction and a 10-pole (2-8-2 spacing cathode) placed into the coronary sinus. The position was confirmed with venography because the cardioversion catheter has a lumen that facilitates contrast injection (Figure 1). A standard 6Fr quadripolar catheter was introduced through the right femoral vein and positioned at the right ventricular apex for R-wave synchronization. Internal cardioversion was performed using a step-up protocol of energy output starting at 2 J, then 5 J, and increased in 5-J increments up to a maximum of 50 J or until sinus rhythm was achieved. Successful cardioversion was defined, as in a previous series, as the restoration of sinus rhythm lasting ⬎1 minute.1 Patients with chronic AF were anticoagulated to a target international normalized ratio of 2 to 3 for 4 weeks before cardioversion. Anticoagulation was discontinued 5 days before the day of planned cardioversion. Enoxaparin 1 mg/kg/day was subcutaneously administered once the international normalized ratio was ⬍2 until the day before the procedure. After successful cardioversion, unfractionated heparin was commenced. The following day, enoxaparin replaced unfractionated heparin and was continued until the international normalized ratio stabilized at ⬎2. The duration of the subsequent anticoagulation was ⱖ4 weeks. Patients who underwent pulmonary vein isolation were not cardioverted until transseptal access had been obtained. After access to the left atrium, intravenous heparin was commenced, and an activated clotting time of ⬎250 ms was maintained throughout the procedure. It was only during adequate anticoagulation that cardioversion was performed. Postoperative anticoagulation then proceeded as previously described. All variables are expressed as mean ⫾ SE. Statistical comparisons between groups were made using the 2-tailed Student’s t test for unpaired data or the Mann-Whitney rank sum test when a normal distribution could not be assumed. Linear regression analysis was used to assess the relation between BMI and energy requirements. Regression coefficients () are expressed with 95% confidence intervals. A p value ⬍0.05 was considered statistically significant. Patient demographics are listed in Table 1. The patients in the failed external cardioversion group weighed significantly more (119 ⫾ 8 kg vs 87 ⫾ 5 kg; p ⬍0.01). They also had a BMI of 36 ⫾ 2, compared with 28 ⫾ 1 (p ⫽ 0.01) in the pulmonary vein isolation group. The duration of AF and left atrial dimensions also varied between the 2 patient groups. 0002-9149/04/$–see front matter doi:10.1016/j.amjcard.2004.04.039
•••
In the present study, we have demonstrated that defibrillation thresholds are increased in patients with chronic AF with high BMIs compared with those with paroxysmal AF and lower BMIs. The number of shocks required to achieve cardioversion was significantly increased in the population with chronic AF and high BMIs in comparison with the patients with paroxysmal AF and lower BMIs. Within the patient population with chronic AF, BMI was found to be predictive of defibrillation thresholds, independent of AF duration. The new single cardioverFIGURE 1. The cardioversion catheter in the coronary sinus is confirmed on venograsion catheter used in this study, phy in a case of failed external cardioversion. The proximal coil lies in the lateral which allowed electrophysiologic reright atrium (RA) and the distal coil in the coronary sinus (CS). A standard quadripocording and coronary sinus venogralar catheter is positioned at the right ventricle (RV) apex for R-wave synchronization. phy, was successful in all cases and LAO ⴝ left anterior oblique; RAO ⴝ right anterior oblique. was used without complications. The duration of AF has been established as an important determinant of the energy required for sucTABLE 1 Baseline Characteristics cessful cardioversion.2,3 In keeping Failed External Pulmonary Vein with our findings, earlier studies by Cardioversion Isolation Levy et al2 found that significantly Variable (n ⫽ 13) (n ⫽ 11) p Value greater energy was required for sucAge (yrs) 56.3 ⫾ 2.4 50.3 ⫾ 3.0 NS cessful cardioversion in the chronic Men/women 12/1 8/3 group compared with those in the Weight (kg) 119 ⫾ 8 87 ⫾ 5 ⬍0.01 paroxysmal AF group. Weight rather 36 ⫾ 2 28 ⫾ 1 0.01 BMI (kg/m2) than BMI was examined in this study Duration of AF episode 21 ⫾ 12 mo 31 ⫾ 7 h ⬍0.01 Left atrial size (mm) 50 ⫾ 2 39 ⫾ 3 0.01 and found not to be predictive. PaStructural heart disease 6 3 NS tients who had repeat internal carFailed antiarrhythmic drugs 0.8 ⫾ 0.1 1.5 ⫾ 0.3 0.01 dioversion had significantly lower defibrillation thresholds at the time of second cardioversion, which correlated with a shorter duration of All patients underwent successful cardioversion. AF before the second cardioversion.4 In the present The failed external cardioversion group required a study, the patients in the failed external cardioversion significantly greater mean energy of 15 ⫾ 1 J, com- group were in chronic AF for a median duration of pared with 8 ⫾ 0.1 J in the pulmonary vein isolation 20 months compared with patients in the paroxysmal group (Figure 2; p ⬍0.001). The failed external car- group, in whom the mean duration of AF episodes dioversion group also required a greater number of was 31 hours. Of particular interest was a marked shocks to achieve success (3.8 ⫾ 0.2 vs 2.7 ⫾ 0.2 difference in BMI between the 2 groups. Because of shocks in the pulmonary vein isolation group; p ⫽ the inherent differences between the 2 groups, we also 0.003). This is by virtue of the step-up protocol. examined the group of patients in whom external Linear regression analysis showed that there was a cardioversion failed. We found that an increase in significant association between BMI and energy redefibrilquired for successful cardioversion ( ⫽ 0.31 [0.01 to BMI correlated significantly with increasing 5 recently relation thresholds. Sharp and Whalley 0.61], p ⫽ 0.047) (Figure 3). The effect of BMI was independent of the duration of arrhythmia (likelihood ported 100% success with a dual-catheter approach with a defibrillation threshold of 12.1 J in those with ratio test: chi-square 1.02, p ⫽ 0.313). The cardioversion catheter was successfully posi- a BMI of 29 in whom external cardioversion failed. tioned in the coronary sinus in all 24 patients. There However, correlation between BMI and defibrillawas no need for a dual-catheter approach or alterna- tion threshold was not performed in this study. The tive positions for internal cardioversion. There were relation between BMI and defibrillation threshold no complications. In particular, there were no ventric- has been previously reported in external cardioverular arrhythmias or failures of synchronization. There sion6 and from the present study appears to be a were also no access hematomas or thromboembolic predictor in internal cardioversion. Obesity is associcomplications. ated with left ventricular hypertrophy and diastolic BRIEF REPORTS
371
further possibility is that of increased cardiac fat around and investing the coronary sinus, which could result in increased impedance and energy requirements. An appreciation of an expected greater defibrillation threshold in patients with larger BMIs could lead to a reduction in the number of shocks. This is particularly relevant for patient comfort when performing internal cardioversion under no or minimal sedation.8 It is our practice to perform internal cardioversion under general anesthesia because of interindividual variability in pain 9 and defibrillation thresholds. In external cardioversion, it has been shown that starting at a greater energy in patients with persistent AF reduces the number of shocks delivered.10
FIGURE 2. The group of patients who had failed external cardioversion (EXT CV) had significantly higher defibrillation thresholds and BMIs compared with the group of patients who had pulmonary vein isolation (PVI).
Acknowledgment: We would like to thank Dr. Lachlan Macgregor from the Department of Biostatistics for his assistance with the statistical analysis.
1. Andraghetti A, Scalese M. Safety and efficacy of
low-energy cardioversion of 500 patients using two different techniques. Europace 2001;3:4 –9. 2. Levy S, Ricard P, Gueunoun M, Yapo F, Trigano J, Mansouri C, Paganelli F. Low-energy cardioversion of spontaneous atrial fibrillation. Immediate and long-term results. Circulation 1997;96:253– 259. 3. Boriani G, Biffi M, Camanini C, Bacchi L, Zannoli R, Luceri R, Branzi A. Predictors of atrial defibrillation threshold in internal cardioversion. Pacing Clin Electrophysiol 2000;23:1898 –1901. 4. Ammer R, Lehmann G, Plewan A, Puetter K, Alt E. Marked reduction in atrial defibrillation thresholds with repeated internal cardioversion. J Am Coll Cardiol 1999;34:1569 –1576. 5. Sharp JC, Whalley DW. Effectiveness and safety of low-energy internal cardioversion of long-standing atrial fibrillation after unsuccessful external cardioversion. Am J Cardiol 2002;90:657–660. 6. Kerber RE. Transthoracic cardioversion of atrial fibrillation and flutter: standard techniques and new advances. Am J Cardiol 1996;78:22–26. 7. Alpert MA, Hashimi MW. Obesity and the heart. Am J Med Sci 1993;306:117–123. 8. Boriani G, Biffi M, Camanini C, Luceri RM, Branzi A. Transvenous low energy internal cardioFIGURE 3. BMI showed a significant correlation with defibrillation threshold (DFT) in the version for atrial fibrillation: a review of clinical group of patients with chronic AF. applications and future developments. Pacing Clin Electrophysiol 2001;24:99 –107. 9. Santini M, Pandozi C, Altamura G, Gentilucci G, Villani M, Scianaro MC, Castro A, Ammirati dysfunction,7 with the potential consequences of in- F, Magris B. Single shock endocavitary low energy intracardiac cardioversion chronic atrial fibrillation. J Interv Card Electrophysiol 1999;3:45–51. creased left atrial pressure and size. Although specu- of 10. Boos C, Thomas M, Jones A, Clarke E, Wilbourne G, More R. Higher energy lative, these atrial effects may result in elevated defi- monophasic DC cardioversion for persistent atrial fibrillation: is it time to start at brillation thresholds in patients with elevated BMIs. A 360 joules? Ann Noninvasive Electrocardiol 2003;8:121–126.
372 THE AMERICAN JOURNAL OF CARDIOLOGY姞
VOL. 94
AUGUST 1, 2004