|Year : 2016 | Volume
| Issue : 1 | Page : 12-14
Experience with implantable cardioverter defibrillator in african-americans: Is there an effect of cocaine usage on defibrillation threshold?
Jonathan Nwiloh1, Adefisayo Oduwole2
1 Department of Surgery, Section of Cardiothoracic Surgery, Atlanta Medical Center, Atlanta, GA, USA
2 Department of Medicine, Section of Cardiology, Morehouse School of Medicine, Atlanta, GA, USA
|Date of Web Publication||25-Jul-2016|
Section of Cardiothoracic Surgery, Atlanta Medical Center, Atlanta, GA
Source of Support: None, Conflict of Interest: None
Objective: Some earlier studies have suggested that cocaine use in African-Americans (AAs) results in higher defibrillation thresholds. We are therefore reviewing our own experience with this racial group for comparison. Materials and Methods: We retrospectively reviewed the medical records of AA patients who had placement by a single operator of implantable cardioverter defibrillator (ICD) at an inner city hospital from January 2006 to December 2015. Results: Seventy-four patients, mean age 59.2 ± 12.9 years, comprising 37 (50.0%) males, underwent ICD implantation of which 67.6% were single chamber and 32.4% dual chamber devices. Diagnosis was nonischemic cardiomyopathy in 68.9% and indication for device therapy was primary prevention in 87.8%. Sixty-six (89.2%) patients were noncocaine users, whereas 8 (10.8%) were cocaine abusers. The mean age, ejection fraction, and defibrillation threshold between the noncocaine and cocaine users were 60.2 ± 12.8 versus 51.3 ± 12.4 (P = 0.642), 21.6 ± 8.3 versus 16.1 ± 4.6 (P = 0.0704), and 23.5 ± 5.0 versus 25.0 ± 8.4 (P = 0.447), respectively. Biotronik device patients had complete follow-up and they had an all-cause mortality of 28.8% (15/52), while 27.0% (10/37) of the survivors had at least one or more antitachycardia pacing or high voltage shock therapies. Conclusion: There was no statistically significant difference in defibrillation threshold testing observed in AA patients in our series between noncocaine and cocaine users as previously seen in some earlier small reviews. Larger studies or meta-analysis of several studies to accumulate a substantial number of AAs using cocaine may be required for a definitive answer to the question.
Keywords: African-Americans, cocaine use, defibrillation threshold testing, implantable cardioverter defibrillator
|How to cite this article:|
Nwiloh J, Oduwole A. Experience with implantable cardioverter defibrillator in african-americans: Is there an effect of cocaine usage on defibrillation threshold?. Niger J Cardiovasc Thorac Surg 2016;1:12-4
|How to cite this URL:|
Nwiloh J, Oduwole A. Experience with implantable cardioverter defibrillator in african-americans: Is there an effect of cocaine usage on defibrillation threshold?. Niger J Cardiovasc Thorac Surg [serial online] 2016 [cited 2020 Dec 1];1:12-4. Available from: http://www.nigjourcvtsurg.org/text.asp?2016/1/1/12/186848
| Introduction|| |
Implantable cardioverter defibrillator (ICD) has been shown in randomized trials to reduce mortality compared to conventional medical therapy in patients with heart failure and severe left ventricular systolic dysfunction and survivors of cardiac arrest. ,, Moreover, guidelines on the use of ICD device therapy have been published by the Heart Rhythm Society (HRS), American College of Cardiology (ACC), and American Heart Association (AHA).  African-Americans (AAs) have been shown to be less likely to receive an ICD when needed, and to have a somewhat higher defibrillation threshold testing (DFT) and higher risk of dying without getting an appropriate shock compared to other racial groups.  Cocaine use which appears more common in AAs has also been suggested to increase DFT compared to nonusers. ,
| Materials and Methods|| |
We retrospectively reviewed the medical records of AA patients who underwent ICD implantation from January 2006 to December 2015 by the lead author. The indications for implantation were consistent with the ACC, AHA, and HRS guidelines on device-based therapy. The procedures were done under conscious sedation for the majority of the patients, whereas a few however required general anesthesia. Venous access was usually first attempted through a percutaneous left infraclavicular subclavian vein stick and when this approach was unsuccessful, a left cephalic vein cut down was then performed. In patients undergoing the procedure under conscious sedation, deeper sedation was attained before DFT. Induction of ventricular fibrillation was achieved by shock on T or direct current shock (DC fibber). However, DFT was not performed in patients with atrial fibrillation because of potential risk for embolization without transesophageal echocardiogram to exclude left atrial thrombus and also in some high-risk patients with ejection fraction (EF) 10% or less. In these patients without DFT at the time of implantation, the device was set to deliver high voltage shocks (HVSs) at maximal output. If the initial shock of 20 J terminated the ventricular fibrillation, no further attempt was made to establish a lower threshold, if there was 10 J safety margin. In patients with high DFT defined as <10 J safety margin between the device maximum delivered output and established DFT, changing the shocking vector and reversing polarity were attempted to improve defibrillation efficiency without the need to increase energy. Subcutaneous coils were also placed in some to enhance DFT. Patients admitting to habitual cocaine use were compared to nonusers. Follow-up of patients was through clinic visits, telephone, and remote access home monitoring and ICD memory downloads from device during clinic visits in Biotronik device recipients. This was not obtainable or available in St. Jude device recipients. All data were entered into an excel spread sheet and then imported into Sigma Plot (Systat Software, Inc., San Jose, CA, USA) for statistical analysis. Categorical variables were reported as frequencies and percentages, whereas continuous variables were expressed as mean ± standard deviations. Univariate analysis by unpaired Student's t-test with two-tailed distribution was used for continuous variables, and Chi-square exact test or Fisher's exact test was used for categorical variables. A probability value of <0.05 was considered statistically significant.
| Results|| |
Seventy-four patients comprising 37 (50.0%) males and 37 (50.0%) females, mean age of 59.2 ± 12.9 years, range of 23-88 years were implanted with ICDs. Fifty-two (70.3%) had Biotronik and 22 (29.7%) had St. Jude devices. Overall, 50 (67.6%) patients had a single chamber and 24 (32.4%) had dual chamber ICDs. The primary diagnosis was nonischemic cardiomyopathy in 68.9% and ischemic cardiomyopathy in 31.1%. Indications were primary prevention in 87.8% and secondary prevention in 12.2%. The mean EF was 21.0 ± 8.1 and DFT was 23.6 ± 5.3. The other baseline patient demographics are shown in [Table 1]. One (1.4%) patient with dilated cardiomyopathy had intraoperative lead microperforation of the right ventricle with cardiac tamponade requiring emergency subxiphoid pericardial window. Three (4.1%) patients including two with insulin-dependent diabetes mellitus required explants months to years after implant for endocarditis. Complete follow-up data were available only for the Biotronik device patients through April 2016. The all-cause mortality was 28.8% (15/52) with two of these patients having had previously documented episodes of HVS for malignant ventricular arrhythmia. 27.0% (10/37) of the remaining survivors had received one or more episodes of antitachycardia pacing (ATP) and/or HVS for ventricular tachyarrhythmia postdevice implant. When the patients were further subdivided into two groups based on cocaine usage, the cocaine group was younger 51.3 ± 12.4 versus 60.2 ± 12.8 for noncocaine group (P = 0642), EF 16.1 ± 4.6 versus 21.6 ± 8.3 (P = 0.0704), and DFT 25 ± 8.3 versus 23.5 ± 4.9 (P = 0.447), all not statistically significant [Table 2].
| Discussion|| |
Following the results of Multicenter Automatic Defibrillator Implantation Trial (MADIT II) showing survival benefits with prophylactic ICD in patients with prior myocardial infarction and left ventricular dysfunction with EF 30% or less,  there has been an increase in the number of patients receiving device therapy for primary prevention of sudden cardiac death. Furthermore, the study by Bardy et al.  showed that in patients with New York Heart Association II or III CHF and left ventricular EF 35% or less that single lead shock only ICD was superior to amiodarone with 23% reduction in mortality. The MADIT II consisting of 1232 patients had no breakdown of the racial composition, whereas the Brady study comprising 2521 patients reported 23% nonwhite race in both amiodarone and ICD groups and 24% in the placebo group. These studies and several others have largely consisted of Caucasians with limited representation of AA. AAs are known to have a higher incidence of hypertension, heart failure, and cocaine usage which may all affect outcomes compared to other racial groups.  Chen et al. in their review of 130 patients including 58 from the Dallas VA Hospital were the first to suggest a relationship of higher DFT in cocaine users compared to noncocaine users. About 72.7% (8/11) of cocaine users in their report were AA compared to 24.4% (29/119) in noncocaine users. They observed in cocaine users, a mean DFT 27.9 ± 7.8 J versus 14.5 ± 4.1 J in noncocaine users, P = 0.00018. Furthermore, a more recent study by Perrine et al.  of 105 patients comprising 73 (70%) AA and 32 (30%) Caucasian identified 17 (16.2%) patients with a history of cocaine use. DFT was higher among AA cocaine users versus nonusers (17.3 ± 8 J versus 12.5 ± 5 J, P = 0.05). The mean EF in cocaine users was 25.6 ± 24.7 versus 30.5 ± 15.2 in nonusers. However, in our review with only 8 (10.8%) of 74 patients been cocaine users, there was no significant difference observed in DFT between cocaine and noncocaine users, 25.0 ± 8.4 versus 23.5 ± 5.0 (P = 0.447). In addition, although the mean EF 16.1 ± 4.6 was lower in the cocaine users compared to 21.6 ± 8.3 in the noncocaine users, it did not reach statistical significance with P = 0.704. The inability in our series to demonstrate a higher DFT in cocaine users could possibly be due to the relatively small numbers (although similar to the other two series), and in addition, our technique of DFT testing might have made it impossible to identify some subtle differences between the two groups. This was a retrospective study, and there was no attempt made during the years of implant to determine the lowest possible attainable DFT. The first shock delivered in all patients was always 20 J and if this successfully terminated the ventricular fibrillation, and there was a 10 J safety margin, no further effort was made to identify a lower shock threshold. This was because many of our patients were high risk with multiple comorbidities, and in addition, considering the lack of expert consensus of any clear benefit to DFT and questions about its predictive accuracy in terminating future malignant tachyarrhythmia given the likelihood of progression of the underlying heart disease over time. In the Biotronik implant patients where we had complete data, the all-cause mortality among the 52 patients during the period of follow-up was close to a third (28.8%), whereas a quarter (27.0%) of the those who survived had one or more episodes of ATP and HVS which likely saved some of these patients.
| Conclusion|| |
While AAs using cocaine have been demonstrated in some small series studies to have a higher DFT, we did not make this correlation in our review. Our study is however limited by its small sample size, been retrospective and the lack of attempt to establish a lower DFT below 20 J in those whose ventricular fibrillation was successfully terminated at this level. Larger studies or meta-analysis of several studies pooling several AA patients with a history of cocaine use may have the statistical power to definitively answer this question.
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Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2]