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European Heart Journal Advance Access originally published online on January 18, 2006
European Heart Journal 2006 27(6):700-707; doi:10.1093/eurheartj/ehi726
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© The European Society of Cardiology 2006. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Clinical predictors and prognostic significance of electrical storm in patients with implantable cardioverter defibrillators

François Brigadeau1,*, Claude Kouakam1, Didier Klug1, Christelle Marquié1, Alain Duhamel2, Frédérique Mizon-Gérard1, Dominique Lacroix1 and Salem Kacet1

1Department of Cardiology A, Hôpital cardiologique de Lille, CHRU, 59037 Lille Cedex, France
2Department of Biostatistics, Lille University Hospital, Lille, France

Received 4 November 2004; revised 10 November 2005; accepted 23 December 2005; online publish-ahead-of-print 18 January 2006.

* Corresponding author. Tel: +33 320 44 50 38; fax: +33 320 44 68 98. E-mail address: f-brigadeau{at}chru-lille.fr


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 Conclusions
 References
 
Aims Insufficient data exists regarding predictors of electrical storms (ES) and clinical outcome in patients treated with an implantable cardioverter defibrillator (ICD). The purpose of this study was to delineate a subgroup of patients likely to experience ES and to determine the impact of ES on mortality in ICD recipients.

Methods and results Baseline characteristics of 307 ICD-treated patients were retrospectively analysed. ES was defined as two or more ventricular tachyarrhythmias within 24 h leading to an immediate electrical therapy (antitachycardia pacing and/or shock), separated by a period of sinus rhythm. Clinical characteristics and survival of 123 patients experiencing a total of 294 episodes of ES (median 2 ES/patient, range 1–9), were compared with those of 184 ES-free patients during a median follow-up of 826 days (inter-quartile 1141 days). Median actuarial duration for the first ES occurrence after ICD implant was 1417 days [95% confidence interval (CI) 1061–2363] with a median follow-up of 816 days (7–4642 days) in ES-free patients. Univariate analysis identified older age, depressed left ventricular ejection fraction (LVEF), ventricular tachycardia (VT) as index arrhythmia, chronic renal failure and absence of lipid-lowering drugs as variables significantly associated with an increased risk of ES. Multivariable Cox analysis confirmed an independent predictive value for chronic renal failure [hazard ratio (HR) 1.54, 95% CI 0.95–2.51, P=0.052], VT (HR 2.20, 95% CI 1.44–3.37, P=0.0003), and LVEF (HR 0.98, 95% CI 0.97–0.99, P=0.027). In contrast, diabetics (HR 0.49, 95% CI 0.27–0.90, P=0.022) were less affected by ES. There was no difference in survival between both groups.

Conclusion ES is frequent but does not increase mortality in ICD's recipients. Patients with severe systolic dysfunction, chronic renal failure and VT as initial arrhythmia are likely to experience ES. Diabetics are less affected by ES.

Key Words: Electrical storm • ICD • Ventricular arrhythmias • Diabetes • Dyslipidaemia • Chronic renal failure


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 Conclusions
 References
 
Implantable cardioverter defibrillator (ICD) is highly effective in primary and secondary prevention of life-threatening ventricular arrhythmias.1–3 About 40–60% of patients implanted with an ICD will receive an appropriate therapy within the 3 years following implantation.4 Most of the time, these therapies are limited to a small amount of shocks or antitachycardia pacing (ATP). However, some patients receive multiple treatments in a short period of time. This situation has been first described as electrical storm (ES). Nevertheless, ES lacks precise definition,5–7 which entails a great variability in the epidemiological data that remain scarce among ICD recipients. Even if most clinical analyses agree on the aetiologies and on some baseline demography of ICD-treated patients affected with ES, discrepancies still exist on the incidence and clinical outcome of this situation.8–10

Regarding the increase of ICD indications,11 ES will certainly become a major issue in intensive care units because of all the clinical, psychological, and economical consequences involved. We intended, therefore, to single out simple clinical characteristics of a subgroup of patients likely to experience ES so as to predict ES occurrence; we analysed its incidence and time of occurrence, then sought after its impact on survival.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 Conclusions
 References
 
Patient selection
Between September 1988 and December 2000, 307 consecutive patients with standard indications for ICD therapy following the current knowledge and/or available guidelines were enrolled in our institution and retrospectively analysed. Indications varied over time. From 1988 to 1992 ICDs were implanted after aborted ventricular fibrillation (VF) or recurrent ventricular tachycardia (VT) resistant to amiodarone or ablative techniques, some patients were treated after failing serial drug testing. In the 1993–97 period, serial drug testing disappeared and ICDs were implanted in patients after the first episode of VT when arrhythmia was still inducible under amiodarone. Since 1997, ICDs were implanted in patients with poorly tolerated VTs or well tolerated VTs occurring in the setting of depressed left ventricular function. Recently, some patients judged at high risk received a prophylactic ICD following guidelines.2,3 All patients were followed for at least 6 months after implant. All patients gave their written consent to receive an ICD and to be studied. No patient was excluded for any reason.

Implant techniques and devices description
Patients underwent implantation of ICD systems from five different manufacturers, the majority being manufactured by current market leaders. Between 1988 and June 1993, 76 implantations (59 primo and 17 replacements) were performed via a thoracotomy approach in the first 59 patients studied. These patients underwent epicardial patch electrodes with abdominal ICDs or endocardial leads linked under skin to a thoraco-abdominal device. These earlier ICDs without antibradycardia or ATP, electrogram storage were programmed with a single VF zone. Since July 1993, 248 patients underwent implantation of newer generation via a transvenous approach as previously described.12 These ICDs were therefore programmed according to the documented or induced arrhythmia with at least two detection zones (VT and VF zone). The cutoff rate for VT detection was set 15–25 b.p.m. below the documented VT rate, and more than one VT zone was programmed if two or more different VTs with cycle lengths differing by >40 ms were documented or inducible. In patients without structural heart disease when only VF was documented, a VF zone only was programmed. Within VT zones, ATP was always programmed as first line therapy. A total of 421 procedures (248 primo and 173 replacements) were performed among these 248 patients; of which 298 ended in the implantation of single chamber and 123 in dual chamber devices.

Concomitant drug therapy
While discharging, Class III antiarrhythmic drugs (amiodarone) were released, except for patients with a history of paroxysmal supraventricular tachycardia. In patients with permanent atrial fibrillation associated with high ventricular rate despite full ß-blocker dose, digoxin was used to prevent inappropriate discharges by the device. For all patients, ß-blockers were always prescribed when not contraindicated. Patients with depressed left ventricular ejection fraction (LVEF) were treated with ACE inhibitors, ß-blockers, spironolactone, and diuretics if needed, according to the current knowledge or available guidelines.

Follow-up
Follow-up began just after implantation and ended in May 2001. Patients were followed every 4–6 months up to 12 years (median 826 days, range 0–4642, and inter-quartile 1141 days). Additional visits were scheduled whenever patients reported shocks, palpitations, syncope or pre-syncope. During each visit, patients were examined and devices interrogated to evaluate the number and type of episodes with stored electrograms. ICD reprogramming, adjustments of drug therapy, biological samples (thyroid, ionograms, uraemia and creatinine levels, C-reactive protein, creatine kinase, and troponin), echocardiography, and coronarography were performed as necessary according to the recorded events and factors deemed causative. Since 1993, stored electrograms were reported on Save to Disk file when available.

Definition of ES and data collection for all patients
Because of the lack of a precise definition of ES, it was defined for the purpose of this analysis as the occurrence of two or more ventricular arrhythmias within 24 h leading to an immediate electrical therapy (ATP and/or shock), separated by a period of sinus rhythm, as previously defined by Dorian,5 Kowey et al.6, and Scheinman et al.7 Patients were divided into two subgroups: the ES group, and the ES-free group. Selected demographic and historical data, i.e. age, gender, underlying cardiac disease, LVEF measured by echocardiography, conventional angiography or radionuclide angiography, NYHA stage, arrhythmia history before implantation, prior supraventricular tachycardia episodes, ß-blockers, ACE inhibitors, antiarrhythmics, and lipid-lowering drugs before and after ICD implant, were entered into a continually updated database. In addition, for patients with arrhythmic events during follow-up, data derived from the stored electrograms were entered into the database. So as to define a clinical subgroup of patients likely to experience ES, we also collected data concerning the cardiovascular risk factors, chronic respiratory, and renal failure. Chronic renal failure was assessed by a creatinine clearance <60 mL/min, and respiratory failure by oxygen pressure on arterial blood samples related to age. Diabetes was assessed by a glycaemia >1.26 g/L, dyslipidaemia was assessed regarding LDL and HDL levels according to the number of cardiovascular risk factors and prior acute coronary event. Obesity was defined as a body mass index >30 kg/m2.

For first-generation ICDs without electrograms implanted between 1988 and 1993, we confirmed the occurrence and identity of the causative arrhythmia only in presence of multiple shocks with simultaneous recording of ventricular arrhythmias on surface ECG's and/or telemetry data. Since 1993, stored electrograms were analysed by senior physicians and became the standard for the determination of the true nature of the causative arrhythmia. An arrhythmia was classified as VT if: (i) the QRS morphology was large and the polarity of QRS deflections changed during tachycardia compared with that during sinus rhythm, (ii) the RR intervals were regular, (iii) there was ventriculoatrial dissociation for dual chamber ICDs, (iv) it started with a sudden change in heart rate (sudden onset). An irregular tachycardia responding to these criteria with a mean heart rate ≤250 b.p.m. was classified as polymorphic VT. If the heart rate was >250 b.p.m. and RR intervals irregular, the arrhythmia was classified as VF.12

Statistics
Statistical analysis was performed by means of SAS software (SAS Institute Inc., Cary, NC, USA). P-values less than 0.05 were considered statistically significant. Results are expressed as frequencies and percentages for categorical variables and median (inter-quartile range) or mean±SD for numerical variables. The delays of occurrence of the first and second, second and third, third and fourth, fourth and fifth ES were compared using paired Wilcoxon rank test. The relationship between the clinical predictors and the occurrence of ES was investigated by means of survival analysis techniques. Survival function was computed as the time of the implantation to the occurrence of an ES. When ES did not occur, observation was censored at the time of the last known follow-up or time of death. For qualitative variables, survival curves were calculated based on the method of Kaplan and Meier. A log rank test was used to determine whether significant differences existed between curves. The prognostic value of continuous variables was studied using the Cox proportional hazards model. Parameters with P<0.15 were introduced in a Cox proportional hazards multivariable regression analysis of survival, with forward selection at the level 0.15 for entry. The stability of the selected model was investigated using the bootstrap method.13 The choice of the variables included in the final model was judged in the light of the frequency of inclusion of each candidate variable in 1000 bootstrap samples on which forward selection was applied. Each Cox stepwise regression with forward selection was performed at level 0.15 and was adjusted for the year of ICD implantation. In the final model, the adjusted hazard ratio (HR) of occurrence of ES and its 95% confidence intervals (CI) were computed. HR refers to the ratio of the hazard functions (instantaneous failure rate at t) that corresponds to a change of one unit of the given variable and conditional of fixed values of all other variables. The Cox model implicitly assumes a log-linear model for continuous covariates. This assumption was checked by using the Martingale Residuals.14 The relationship between the Martingale Residuals and each continuous covariate was investigated by means of a lowess smoothing (LOESS SAS procedure) and the linearity of this relation was tested using the Pearson correlation coefficient. The validity of the proportional hazard assumption was checked using the Scaled Schoenfeld Residuals. The proportional hazard assumption was tested for each covariate (numerical or binary) by correlating the corresponding Scaled Schoenfeld Residuals with the rank of time.15 These tests were illustrated by producing graphs of Scaled Schoenfeld Residuals against the rank of time. The plots were augmented with a spline smooth and the corresponding 95% CIs.15

Additional analyses including diabetic patients were also made, in order to investigate the impact of diabetes on ES occurrence. Comparisons between diabetic and non-diabetic groups were done using bivariate analysis (Student's t test for numerical variables and {chi}2 test for categorical variables) and multivariable logistic regression.

Finally, the influence of ES on the occurrence of death was investigated using survival analysis. Because the delay to reach the ES is different across the patients and can influence the survival, we performed a Cox regression model using the ES state as time-dependent covariate.


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 Conclusions
 References
 
Patient's characteristics
Our population consisted of 307 consecutive patients implanted with an ICD between September 1988 and December 2000. Table 1 summarizes the baseline characteristics of the study population. Four hundred and twenty-one procedures were performed including primo implantations and devices and/or leads replacements.


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  		Table 1 Clinical characteristics of the 307 consecutive ICD studied patients
 
ES occurrence
A total of 123 patients experienced at least one ES episode. Overall, 294 episodes were recorded (median two ES per patient, range 1–9) and 58% of patients of the ES group experienced two or more ES episodes. The amount of ventricular arrhythmia per ES is shown on Figure 1. In 81 episodes of ES recorded with first-generation devices, the nature of arrhythmia was confirmed by body surface ECG, but the exact number of ventricular arrhythmia episodes could not be assessed exactly. Finally, among the 294 ES, 164 needed ATP and shocks, 76 and 54 were, respectively, treated by ATP and shocks only.


Figure 7261
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  		Figure 1 Number of ventricular arrhythmias per ES.

 
Median actuarial duration for the first ES occurrence after ICD implantation was 1417 days (95% CI 1061–2363) with a median follow-up of 816 days (7–4642 days) in ES-free patients. Figure 2 illustrates the time of occurrence of first episode of ES and the total amount of ES. Despite a tendency to shortening (median 199 days, median 163 days, median 143 days, median 65 days between the first and second, second and third, third and fourth, fourth and fifth ES, respectively), we did not find any statistically significant difference between the free intervals separating the different episodes of ES in patients experiencing multiple ES.


Figure 7262
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  		Figure 2 Comparison of times of occurrence of first episodes of ES with total amount of ES. Please note that the majority of ES occurs during the first year post-implant.

 
Types of ES, precipitating factors, and ES management
In a vast majority of cases, the recorded arrhythmias were VT's (90%). VF's have been found in only 8% of ES episodes. The remaining events were torsades de pointes or polymorphic VTs. Despite a careful analysis of symptoms, ECG's, and blood samples in all ES sufferers, we found a putative precipitating factor in only 36%. Among the 294 ES, we found 13 proven ischaemias related to acute coronary syndromes, some of them ending up in a coronary angioplasty, 19 acute infections attested by high temperature, physical examination and increased C-reactive protein, hypo- or hyperkalemia in 13, hyperthyroidism in 13, and 46 acute heart failures. Results summerizing ES management are presented in Table 2.


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  		Table 2 Management of the 294 episodes of ES
 
Clinical predictors of ES
Univariate analysis, as summarized Table 3, pointed out a subgroup of patients likely to experience ES. Older age, altered LVEF, VT as presenting arrhythmia, chronic renal failure, and absence of lipid-lowering drugs were predictive of ES. On the other hand, VF as presenting arrhythmia and surprisingly diabetes appeared to be more frequent in the ES-free-group. The multivariable analysis (Tables 4 and 5) confirmed the independent predictive value for LVEF, chronic renal failure and VT as initial arrhythmia, and the protective effect of diabetes against ES.


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  		Table 3 Survival analysis of the univariate predictors of ES
 

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  		Table 4 Multivariable Cox stepwise analysis (variables are presented in order of selection)
 

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  		Table 5 Independent predictors of ES (multivariable Cox analysis and bootstrap method)
 
We further analysed the characteristics of the 54 diabetic patients (Table 6). In order to study whether the two populations corresponded to different profiles, multivariable logistic regression was performed. From this subanalysis, only hypertension (P=0.01) and obesity (P=0.002) were found to be significantly independent different parameters between diabetic and non-diabetic patients. Neither LVEF nor antiarrhythmic drug therapy (especially ß-blockers at discharge) were different in the diabetic and non-diabetic groups. We also tested the hypothesis that sulfonylurea of the second generation (IKATP-blockers) were involved as antiarrhythmic drugs in diabetics. We did not find any significant difference in the ES and ES-free diabetic groups.


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  		Table 6 Univariate comparison of diabetics and non-diabetic patients
 
Clinical outcome of ES
A total of 53 patients died during the follow-up (25 in the ES group and 28 in the ES-free group). Kaplan–Meier Survival curve for the 307 patients is represented in Figure 3. The estimated survival rate was 92.6% in the first year, 77.7% at 5 years, and 63.3% at 10 years. We did not find a significant effect of the occurrence of ES on the survival rate (Cox regression by considering ES as a time-dependent covariate, P=0.98).


Figure 7263
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  		Figure 3 Kaplan–Meier survival curves in the 307 ICD patients. The occurrence of ES did not influence survival (Cox analysis by considering ES as a time dependent variable P=0.98).

 

   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
Conclusions
 References
 
The main findings of this study are the definition of a clinical profile of ICD recipients at risk to develop ES. Thus patients presenting with low LVEF or chronic renal failure are likely to experience ES. At the opposite, patients with VF as presenting ventricular arrhythmia and patients treated with lipid-lowering drugs are at low risk of ES. We also found that diabetes was protective against ES. At last, we did not find that ES was predictive of mortality in ICD recipients.

Baseline characteristics of the population
The 307 studied patients are similar to those presented in major clinical prevention studies for baseline characteristics.1–3 Mean age is close to 60, with 87% of male gender. The most frequent cardiopathy is coronary artery disease. Implant indications correspond to the available guidelines. The annual survival percentage rate is 92.3% at 1 year and 82.3% at 10 years. For a same LVEF level, we found a survival rate similar to Böcker et al.16 report.

Natural history of ES
The precise definition of ES is still evolving.5–7 In the present series, 123 (40%) of 307 patients experienced at least one ES, which is more than the incidences found by Credner et al.8 (10%) and Exner et al.9 in the AVID trial (20%). Both of them used another definition of ES: the occurrence of at least three ventricular events in a 24-h period. Moreover, the mean follow-up of our study is longer than their ones (38 vs. 13 and 31 months, respectively).8,9

The median actuarial duration for the first ES occurrence after primo ICD implant was 1417 days, which is in agreement with a previous study.10 The discrepancy we have with Exner et al.9 and Credner et al.8 studies is probably linked to different follow-up duration. Considering the median time of occurrence of first ES, we can also exclude like these authors, any inflammatory or immediate post-surgical phenomenon suspected by Kim et al.17 We also found a trend to the shortening of free intervals separating episodes of ES, although it did not reach statistical significance. This probably results in the spontaneous worsening of cardiopathies despite optimal treatments.

We only found one-third of possible precipitating factors in which acute heart failure and ischaemia represent 56% of all triggers found. This is in agreement with Credner et al.8 study, who found a significant reduction in baroreflex sensitivity in patients likely to experience appropriate ICD's therapies. This should lead to large prescription of ß-blockers in patients liable to suffer from ES. It is well known that vagal reflex activity is depressed in patients with heart failure and/or coronary artery disease. Increased sympathetic tone has also been shown to enhance electrical instability.

We found a peak occurrence of ES during the first 6 months after ICD implantation. It may be possible that the withdrawal of amiodarone after implantation in the absence of paroxysmal supraventricular tachycardia explains this phenomenon.

Clinical profile of the ES group
The first predictive factor is a low LVEF. The high frequency of ventricular arrhythmia is now well known in heart failure.18 From then on, it makes sense to find LVEF as a clinical predictor of ES. This result is in accordance with Exner et al.9 Another one is chronic renal failure. This finding in patients with a creatinine clearance <60 mL/min is in accordance with the studies of Soman et al.19,20 With a follow-up of 8 years, in a coronary care unit, these authors found a relative risk of 2.07 of sustained VT in a group of patients suffering from chronic renal failure compared with patients with normal renal function. Moreover, in patients with a prior myocardial infarction, they found a higher arrhythmic mortality in patients with chronic renal failure.

Clinical profile of the ES-free group
By univariate analysis, three protective factors against ES were found in this study: VF as presenting arrhythmia, treatment with lipid-lowering drugs at discharge, and diabetes (Table 3). Multivariable analysis confirmed only VF as index arrhythmia and diabetes (Table 4). In accordance with our results, Exner et al.9 found a much higher percentage of patients in whom an ICD was implanted for VT as initial arrhythmia than VF among ES sufferers. In the AVID trial, Raitt et al.21 similarly observed less frequent VT recurrences in patients enrolled after a VF episode as compared with those who presented with VT, suggesting important differences in the electrophysiological characteristics between the two patients' population. Indeed, in an experimental study, Denniss et al.22 have demonstrated a longer epicardial activation time, a larger infarct size, and viable muscle bundles of larger diameter at the infarct edge in animals with inducible VT when compared with animals with inducible VF. These results, however, are conflicting with a recent report by Verma et al.23 who studied 2028 ICD recipients among whom 208 (10%) presented with ES. They found that VF was responsible for ES in a sizable proportion of patients as much as 48%. One explanation of this discrepancy probably includes the lower mean LVEF of their affected patients (25±12%), which may indicate a cohort with more advance disease and explain the high-mortality rate (27%) during a mean shorter follow-up. Furthermore, the use of ß-blockers was less frequent (54%). Indeed, ß-blocker therapy has been found to have a prophylactic effect against VF in coronary artery disease.24

In this study, diabetes has been found to be significantly higher in the ES-free group. This result appeared to be independent of ß-blocker therapy which is known to be more effective in diabetics affected with a coronary artery disease,25 and of oral antidiabetic treatment as sulfonylurea of the second generation, which reduce extracellular potassium and action potential shortening, known to be the major factors of ventricular arrhythmia's genesis during acute ischaemia.26 This is conflicting with the previous epidemiological analysis that found diabetes as a major risk factor for sudden death.27,28 Apart from direct ischaemic worsening, it is likely that the propensity for sudden death in individuals with coronary artery disease might be enhanced by diabetes-associated autonomic neuropathy, or microvascular disease affecting the conduction system of the heart. However, this result is in accordance with the findings of Whang et al.,29 who analysed the diabetics' outcomes in the Coronary Artery Bypass Graft Patch Trial database. Whang et al.29 found that the adjusted risk for arrhythmic death in diabetics was almost half that in non-diabetics. Arrhythmia was less often the reason for re-hospitalizations, and fewer ventricular arrhythmias occurred during hospitalizations in the diabetics group. The recent SCD-HeFT Study30 evaluating the impact of prophylactic ICD in patients with LVEF<35% regardless of its aetiology demonstrated that non-diabetes patients had a greater benefit to receive an ICD compared with diabetics [HR 0.67 (95% CI 0.05–0.90) vs. HR 0.95 (95% CI 0.68–1.33), respectively]. We could hypothesize that diabetic ICD recipients included in our study were survivors of a high-mortality group and therefore at relative low risk for ES. However, these results in primary prevention studies rule-out this explanation. A possible metabolic explanation would be an enhanced metabolism of free fatty acids in diabetes especially if heart failure is present. Yet, Paolisso et al.31 found a significantly higher occurrence of ventricular arrhythmias in diabetics after the increase of free fatty acid plasma concentration. Some authors also found that streptozotocin induced diabetic isolated rat's heart was more resistant to ischaemia-reperfusion arrhythmias.32

It also seems that metabolic factors are involved in ES occurrence. De Sutter et al.33 reported in 78 ICD patients a significant reduction of VT/VF recurrences in 27 receiving lipid-lowering drugs, especially those with concomitant ß-blockers. Considering the improvement on vulnerable plaque stabilization, platelet reactivity, and endothelial dysfunction, statins could diminish the number of myocardial ischaemia and, therefore, lower the number of malignant ventricular arrhythmias.34,35 It is now admitted that statins and fenofibrate may have anti-inflammatory effects.36 Martin et al.37 demonstrated that PPAR{alpha} is an important target for statins and fenofibrate. Now, PPAR{alpha} activation negatively interferes with NF{kappa}B and AP-1 mediating anti-inflammatory actions. We have shown in porcine tachycardia-induced heart failure experiments that PPAR{alpha} activation diminished the number of ventricular arrhythmia under condition of oxidative stress.38 Hence it is plausible that lipid-lowering drugs lower the number of ES through an anti-inflammatory action.

Mortality in the study groups
We did not find any statistical differences in the cumulative annual survival rates between storm and storm-free groups. These results are in accordance with previous studies.8,10 Oppositely, Exner et al.9 found that 3 months after ES occurrence, the mortality rate was 5.4 times higher than in patients without ES. First of all, LVEF is lower in the AVID storm population (29±10 vs. 34±16%, respectively). Further, antiarrhythmics are also relatively more infrequent in their ES group. Amiodarone was present in only 2/90 patients (2%) and ß-blockers in 43/90 patients (48%), whereas they represented 21 and 69% of our affected patients, respectively. However, we did not consider as in the AVID trial, the 3 months period after ES as particularly favourable for the genesis of ES. Verma et al.23 also reported increased mortality in patients with ES. Similar to the AVID trial, mean LVEF was lower (25±12%) and ß-blockers less frequent.

Study limitations
These results have to be re-evaluated in a prospective study to confirm the clinical profile of ES victims and ES-free victims and to determine the lipid-lowering drug's pharmacological class responsible for the arrhythmia's reduction. It also might be important to test some physiopathological hypotheses developed in the discussion to explain the relative less frequency of ES in diabetics.


   Conclusions
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conclusions
References
 
ES is such a frequent and recurrent event in ICD recipients that it will bring about a great involvement of intensive care units. Our data provide for the first time, evidence that altered LVEF or chronic renal failure are associated with an increase of ES, and that VF as initial arrhythmia, diabetes, and lipid-lowering drugs at discharge are more frequent in the ES-free patients. ES does not seem to worsen the ICD recipient's prognosis.

Conflict of interest: none declared.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conclusions
 References
 

  1. The Antiarrhythmics Versus Implantable Defibrillators (AVID) Investigators. A comparison of antiarrhythmic drug therapy with implantable defibrillators in patients resuscitated from near-fatal ventricular arrhythmias. N Engl J Med 1997;337:1576–1583.[Abstract/Free Full Text]
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  7. Scheinman MM, Levine JH, Cannom DS, Friehling T, Kopelman HA, Chilson DA, Platia EV, Wilber DJ, Kowey PR. Dose-ranging study of intravenous amiodarone in patients with life-threatening ventricular tachyarrhythmias. Circulation 1995;92:3264–3272.[Abstract/Free Full Text]
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