Europace Advance Access originally published online on May 16, 2007
Europace 2007 9(7):540-543; doi:10.1093/europace/eum083
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IMPLANTABLE CARDIOVERTER DEFIBRILLATOR
Defibrillation testing at the time of implantation of cardioverter defibrillator in the clinical practice: a nation-wide survey
1 Department of Cardiology, Arrhythmologic Centre, Ospedali del Tigullio, 16033 Lavagna, Italy; 2 Boston Scientific Italy, Milan, Italy; 3 Ospedale Cisanello, Pisa, Italy; 4 Casa di Cura Santa Maria, Bari, Italy; 5 Ospedale Consorziale Policlinico, Bari, Italy; 6 Istituto Clinico Humanitas, Rozzano (MI), Italy; 7 Casa di Cura Villa Pini d'Abruzzo, Chieti, Italy; 8 Ospedale Maggiore della Carità, Novara, Italy; 9 Azienda Ospedaliero-Universitaria, Fondazione IRCAB, Udine, Italy
Manuscript submitted 25 January 2007. Accepted after revision 3 April 2007.
* Corresponding author. Tel: +39 0185 329 567; fax: +39 0185 306 506. E-mail address: mbrignole{at}asl4.liguria.it
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Abstract |
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Aims Despite an effective defibrillation testing (DT) is considered mandatory to be consistent with the rules of good clinical practice, some physicians are concerned about the risk of complications related to the induction test, and in real world clinical practice, several implant procedures are performed without any induction test. We conducted a systematic nation-wide retrospective survey in order to determine the DT rate and its complications.
Methods and results An ad hoc questionnaire was sent to all 343 Italian implanting centres and the data from the 229 (67%) centres that answered were analysed. During the year 2005, a total of 7857 patients underwent a first implantation of cardioverter defibrillator (ICD), 38% of which with cardiac resynchronization therapy (CRT). Of these, 2356 (30%) were implanted without any induction test. In 35 (15%) centres, the induction test was performed in < 25% of the patients, whereas in 136 (59%) centres, it was performed in > 75% of the patients. At multivariable analysis, performed in a subset of 1206 patients from 107 centres, CRT device (OR = 1.82) and primary prevention (OR = 1.47) were independent predictors of the decision to not perform DT. However, altogether, the clinical variables accounted only for 35% of the total variance, whereas the remaining 65% was probably unrelated to clinical factors. There was a total of 22 (0.4%) life-threatening complications as a consequence of the induction test: 4 deaths (0.07%), 8 cardiopulmonary arrests requiring resuscitation manoeuvres (0.15%), 6 cardiogenic shocks (0.11%), 3 strokes (0.05%), and 1 pulmonary embolism (0.02%).
Conclusion In real world practice, DT is not performed in a substantial number of patients, most of these in the absence of legitimate reasons. The clinical impact of DT vs. no DT remains unclear until the not negligible complication rate is compared against the long-term potential benefit.
Key Words: Defibrillation testing, Implantable cardioverter defibrillator, Ventricular fibrillation
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Introduction |
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The standardized requirements for the implantation of cardioverter defibrillator (ICD), with or without cardiac resynchronization therapy (CRT), include defibrillation testing (DT). This procedure has been set from the early days of ICD therapy in order to test the reliability of the device and to measure the defibrillation threshold. Defibrillation testing is considered mandatory to be consistent with the rules of good clinical practice.
Nowadays, because the implantation procedure of ICD has been markedly simplified and the surgical risk is very low, DT can be considered to the most critical part of the implantation procedure itself. Although the risk associated with DT is usually low, serious complications may occur as a consequence of this practice. These complications include transient ischaemic attack or stroke, cardiopulmonary arrest due to refractory ventricular fibrillation (VF) or pulseless electrical activity, cardiogenic shock, embolic events, and death. This knowledge comes from small single-centre retrospective surveys1
and from anecdotal experiences. However, in the absence of data of large populations from multicentre registries, the real magnitude of intra-operative complications related to DT is still largely unknown.
Despite the standardized approach still requires VF induction test, data coming from the real world experience suggest that an increasing number of first implantation procedures are performed without any induction test. It seems that some physicians are concerned about practicing DT in selected patients considered at very high clinical risk. For example, in two single-centre populations, Russo et al.2 did not perform any induction test in 4.7% and Pires and Johnson3 in 24% of their patients, respectively. Reasons for no induction included intra-operative hypotension or haemodynamic instability, known cavity thrombus or previous inadequate anticoagulation therapy, recent cardiovascular accident, severe comorbidities, and absence of anaesthesia support.
We conducted a systematic nation-wide retrospective survey in order to determine: (i) how often and for what reason intra-operative DT was or was not performed and (ii) the complication rate related to induction testing.
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Methods |
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An ad hoc questionnaire was sent to all 343 centres implanting ICDs listed in the database of Italian ICD Registry of Associazione Italiana di Aritmologia e Cardiostimolazione (AIAC), which virtually represents the totality of Italian implanting centres. Data from the 229 (67%) centres that answered were analysed. The National ICD registry of AIAC collects data of ICD implantation on the basis of the European ICD Registry form.
The survey was limited to patients undergoing initial ICD implantation during the year 2005. Questionnaire and data collection were performed through the web from June to October 2006. The centres were asked to communicate their data regarding total number of ICDs (including those with CRT features), number of implantations in whom DT was performed intra-operatively, and number and type of DT-related complications. Defibrillation testing was defined as at least one induction of VF at the time of implantation procedure. DT-related complications were considered those life-threatening events occurring immediately after VF induction till the end of the operative procedures (patient exits form the cath lab). In a subset of 1206 patients, in whom data regarding age, sex, dilated vs. ischaemic cardiopathy, New York Heart Association (NYHA) classification, reason for implantation (primary or secondary prevention), type of device (ICD or ICD plus CRT), and left ventricular ejection fraction were available, these variables were correlated with the decision to not perform DT.
Statistical methods
Descriptive statistics were computed as absolute and relative frequencies for all categorical variables. A logistic model was fitted to assess the ability of a series of covariates in predicting the choice of not performing DT at implant. The non-correlated variables that were significant at the 10% level at univariable analysis were included in a multivariable model. A P-value less than 0.05 was considered statistically significant; 95% confidence intervals were computed for several estimates.
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Results |
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Among a total of 8820 first ICD/CRTs implanted in Italy during the year 2005, we analysed the data of 7857 (89%) implantations (38% of whom CRT) performed in the 229 centres which participated in the survey.
Defibrillation testing at implantation
Defibrillation testing was not performed at implantation in 2356 (30%) patients (Table 1). Of these, 195 were scheduled for a delayed DT, which was performed from 7 to 50 days after discharge; therefore, 2161 (27.5%) patients did not undergo any induction test. The non-induction rate was 24% in ICD implantation and 39% in CRT implants. In 18 centres, DT was not performed in any patient. The induction test was performed in < 25% of the patients in 35 (15%) centres and in > 75% of the patients in other 136 (59%) centres (Figure 1). A single induction with the 10 J safety margin technique was used for DT in 86% of patients.
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At univariable analysis performed in a subset of 1206 patients from 107 centres, age
70 years, CRT, primary prevention, left ventricular ejection fraction 
30%, dilated cardiomyopathy, and NYHA class > 2 were related to a lower induction rate. At multivariable analysis, CRT implantations (OR = 1.82) and primary prevention (OR = 1.47) were independent predictors of the decision to not perform the DT (Table 1). However, altogether, the clinical variables accounted only for 35% of the total variance, whereas the remaining 65% was probably unrelated to clinical factors.
Complications at implantation
Among 5501 patients who underwent DT at implantation, there was a total of 22 (0.4%) life-threatening intra-procedural complications as a consequence of the induction test (Table 1). In particular, four patients (0.07%) died because of the failure to resume a valid electro-mechanical activity after defibrillation. Other complications were cardiopulmonary arrest requiring resuscitation manoeuvre in 8 (0.15%), cardiogenic shock in 6 (0.11%), stroke in 3 (0.05%), and pulmonary embolism in 1 (0.02%).
The failure rate of ICD defibrillation, requiring the use of a backup external defibrillator, was 2.7%, which determined a system revision (i.e. additional lead insertion, etc.) in 2.3% of patients.
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Discussion |
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This nation-wide survey is the largest ever performed and covers 89% of all first implantations performed during the year 2005 in Italy. The main result is that, in real world clinical practice, DT was not performed at implantation in 30% of patients, most of these in the absence of legitimate reasons, despite DT still being considered part of the standard procedure of ICD implantation. Even considering those few patients who underwent a delayed DT after hospital discharge, this rate remains unexpectedly high at 27.5%. There is a wide variation between centres, and more than a quarter of Italian centres do not perform DT in
50% of their patients (Figure 1). These figures are much higher than those expected from the literature2–4 and reflect a spontaneous non-conformist opinion of several physicians that goes beyond the current recommendations of the ICD companies. Given the high numbers involved, this behaviour deserves explanation and remedial action.
An explanation for limited DT use is the increasing role of primary prevention strategy5,6 that includes patients with very low ejection fraction and advanced NYHA class.7 The selection of sick patients due to expanded ICD indications has been recently confirmed in a comparison of USA and Italian practices.8 However, altogether, the clinical variables accounted only for 35% of the total variance, whereas the remaining 65% was probably unrelated to clinical factors. Therefore, the main reasons for the violation of the current standard in so many cases seem to be the concern that severe complications may result from the intra-operative DT procedure and the conviction of the small risk of death due to the failure of the ICD to interrupt a VF during the long-term follow-up.
In this study, DT-related life-threatening complication rate was not negligible, accounting for 0.40% of cases, considering that DT in the analysed cohort of patients was preferably performed in the less sick patients (Table 2). The complication rate might have been even higher if the patients with severe heart failure and very low ejection fraction were not preventively excluded from undergoing DT. In the literature, there are few reports from small studies concerning intra-operative complications. A report1 on 440 consecutive single-centre ICD implantations showed 0.2% peri-operative deaths, 0.5% difficulty in defibrillation with requirements for more than three external shocks, and 0.7% peri-operative ischaemic attack. In another single-centre study,2 performed on 835 ICD implantations, there were 3 (0.35%) peri-operative deaths (within 30 days from implant). It has been reported that shocks during DT may cause haemodynamic compromise,9 especially in patients with severe heart failure, as are those candidates to CRT. Moreover, anaesthesia has a cardiac depressive effect in addition to VF induction.10 Patients at implantation could have worse clinical conditions that could improve later with CRT, thus decreasing the risk of complications related to DT; for example, a DT delayed up to 2 months after CRT device implant, when patient's clinical condition improved because of CRT, showed effectiveness without compromising safety.11
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In contrast, few data are available on the risk of death due to the failure of the ICD to interrupt a VF during the long-term follow-up. Sudden death in patients with ICD is reported to range approximately from 1.8 to 2.6% during 1–3 years of follow-up.3
,12,13 Of these, an analysis of the mechanisms of sudden death, with data retrieved from ICD diagnostic memory, showed that only a quarter of the cases could be attributed to shock failure during VF.12 Therefore, we can assume that the sudden death rate potentially attributable to shock failure is low, ranging from 0.45 to 0.65% during 1–3 years of follow-up. In addition, there are no data that specifically demonstrate increased mortality among patients with high DT thresholds at implantation, and in a recent study,3 success of ICD therapies and sudden death-free survival were similar in patients who had defibrillation threshold measurement, safety margin testing, or no testing.
Study limitations
Owing to the retrospective nature of this study, the complication rate might be underestimated. Moreover, even if the survey included 89% of all implantations performed in Italy in 1 year, extensive clinical data were available for multivariable analysis in only 15% of these, thus raising the possibility that the results of the analysis might have not been fully representative of the general population of patients undergoing ICD implantation. However, despite these limitations, this analysis is by far the largest ever undertaken.
Practical implications
Is it time to change current standard of performing DT at the time of ICD implantation? The question has been previously raised by authoritative authors.2–4,14,15 There is no evidence-based answer yet. Reasons in favour and contrary to DT are summarized in Table 3. The clinical impact of DT vs. no DT will remain unclear until the not negligible intra-operative complication rate is compared against the long-term potential benefit of DT. Until long-term follow-up data regarding the safety and efficacy of ICD implantation in large groups of patients in whom DT is not performed are available, DT should be considered as a standard practice. However, data from the literature and from the present study support the need to perform such large multicentre studies and the urgency for scientific subspecialty societies to give precise recommendations.
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Conclusion |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionAcknowledgementsReferences |
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In real world practice, DT is not performed in a substantial number of patients, most of these in the absence of legitimate reasons. This finding, much higher than that expected from the literature, reflects a spontaneous non-conformist opinion of several physicians that goes beyond the current recommendations. Given the high numbers involved, this behaviour deserves explanation and remedial action. The results of this study give the background for future trials aimed to evaluate the clinical benefit of performing DT and underline the urgency for scientific subspecialty societies to give precise recommendations.
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Acknowledgements |
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TopAbstractIntroductionMethodsResultsDiscussionConclusionAcknowledgementsReferences |
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The authors acknowledge all the physicians of the centres participating in the survey and IRCAB foundation (Italian ICD registry). The study was officially approved and and endorsed by AIAC and was supported by a grant from Guidant-Boston Scientific Corporation. AIAC national board: M.B., N. Bottoni, A. Campana, A. Curnis, M. Di Biase, E. Feraco, M. Gulizia, R. Pedretti, M. Santini, M. Tritto, R. Verlato.
Conflict of interest: G.R. is an employee of Guidant–Boston Scientific Corporation.
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References |
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