© 2004 by European Society of Cardiology
The role of implantable cardioverter defibrillator for primary vs secondary prevention of sudden death in patients with idiopathic dilated cardiomyopathy
aStruttura Complessa di Cardiologia, Az. Ospedaliera "Ospedali Riuniti" Trieste, Italy; bStruttura Complessa di Cardiologia, Az. Ospedaliera "S. Maria degli Angeli" Udine, Italy
Manuscript submitted 14 October 2003. Accepted after revision 18 April 2004.
*Corresponding author. S. C. di Cardiologia, Ospedale di Cattinara, 34100 Trieste, Italy. Tel.: +39-0403994828; fax: +39-0403994878. E-mail address: massimo.zecchin{at}libero.it (M. Zecchin).
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Abstract |
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AIM: To analyse the characteristics and outcome of patients with idiopathic dilated cardiomyopathy (DC) considered at high risk of sudden death (SD) and treated with implantable cardioverter defibrillators (ICD) for primary prevention (Group A) in comparison with patients treated with ICDs because of previous sustained ventricular tachyarrhythmias or syncope (Group B).
METHODS: Group A consisted of 27 patients with at least two of the following criteria: left ventricular end-diastolic diameter (LVEDD) 
70 mm (74%), LV ejection fraction (LVEF) 
30% (78%), non-sustained ventricular tachycardia (VT) (56%), long history of disease (48 months since diagnosis, 85%) and family history of SD (11%). Group B consisted of 27 patients treated with ICDs because of sustained VT/fibrillation (n=18) or syncope (n=9).
RESULTS: NYHA class, LVEF, LVEDD and amiodarone treatment were similar in the two groups. Patients in group A were younger (46 ± 15 vs 59 ± 17 years, P=0.0008), were more often treated with ß-blockers (89% vs 62%; P=0.02) and had a longer interval since diagnosis (86 ± 60 vs 40 ± 50 months; P=0.004). Twelve month rates of appropriate intervention (AI) were 41% in Group A and 57% in group B (P NS). In group A, after a mean follow-up of 21 ± 14 months, patients showing the combination of LVEF 30% and LVEDD 70 mm had the highest frequency of AI (76% vs 10%, P=0.005). In group B, after a mean follow-up of 33 ± 23 months, 78% of patients with syncope had AI. Total and sudden deaths were 11% and 4% in group A and 19% and 4% in group B (P NS).
CONCLUSIONS: Patients with idiopathic DC treated with ICD for primary prevention because they were considered at high risk of SD according to clinical criteria showed a high rate of AI, similar to that of patients treated for secondary prevention. The highest rate of AI was seen in patients with both severe dysfunction and dilatation and in those with previous syncope.
Key Words: dilated cardiomyopathy, sudden death, implantable defibrillator, primary prevention of ventricular tachyarrhythmia, secondary prevention of ventricular tachyarrhythmia
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Introduction |
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Although mortality in idiopathic dilated cardiomyopthy (DC) has declined in the last two decades [1,
2] sudden cardiac death accounts for approximately 30% of all deaths in these patients. While it is more frequent in the advanced stages of the disease [3], it represents the first cause of death for less severely affected patients [4]. However, because of the lack of reliable markers, risk stratification in the individual patient is still an unresolved issue.
Amiodarone [5] and ß-blocking agents [6–8] may have a role in reducing sudden death incidence in patients with DCM, but data are not conclusive.
In non-ischaemic cardiomyopathy, the role and the benefit of an implantable cardioverter-defibrillator (ICD) for secondary prevention of sudden death is well established [9–11], while it is still uncertain which patients can benefit from ICD treatment for primary prevention [12,13].
Some uncontrolled studies [14,15] suggested that the rate of death due to heart failure was higher during the first years after diagnosis while patients who had long-term persistence of severe left ventricular dysfunction and dilatation and a history of non-sustained ventricular tachycardia (VT) had the highest risk of sudden death.
Recently, Grimm and others [16] showed that in patients with DC, left ventricular ejection fraction <30% and non-sustained VT treated with ICD for primary prevention had an incidence of appropriate interventions similar to that of patients treated with ICD because of previous sustained VT, ventricular fibrillation (VF) or syncope. However, in that study only 33% of patients in the primary prevention group were on optimal medical therapy including ß-blockers.
The aim of our study was to evaluate the usefulness of primary prevention by ICD in patients with DC considered at high risk of sudden death, in spite of optimal medical treatment including ß-blockers and ACE inhibitors, in comparison with patients treated with ICDs for secondary prevention.
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Methods |
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The study group consisted of 54 patients with DC evaluated in two centres in north-east Italy (Trieste and Udine) and treated with ICDs from September 1995 to December 31, 2002. In all patients the diagnosis of idiopathic DC was made according to the WHO definition [17]
. At enrolment 45 patients (83%) underwent coronary angiography to exclude significant coronary artery disease (stenosis >50% in an epicardial vessel). In young patients (<35 years old) with no risk factors or in familial cases, ischaemic heart disease was non-invasively excluded. Twenty-three (43%) underwent an endomyocardial biopsy to rule out active myocarditis and other specific myocardial diseases. In patients with a long history of heart failure and a low clinical probability of active myocarditis, endomyocardial biopsy was not performed.
Patients with moderate to severe hypertension (>170/100 mmHg), significant alcohol intake (>100 g/day in the previous 6 months), severe valvulopathy, cor pulmonale, prognostically relevant systemic diseases, arrhythmogenic right ventricular cardiomyopathy, ‘tachycardia induced’ cardiomyopathy, with suspected cardio-toxicity or ischaemic cardiomyopathy diagnosed according to the WHO definition [17] were excluded from the analysis.
Most patients had been treated with ACE inhibitors; digoxin and diuretics were given as needed. ß-blockers (metoprolol or carvedilol) were given to all patients without contraindications and titrated to the highest tolerated dosage. Amiodarone (or rarely sotalol) was administered in the presence of unsustained but particularly frequent, complex or symptomatic ventricular arrhythmias or symptomatic supraventricular arrhythmias. No patient was treated with class I antiarrhythmic drugs.
Patient population was divided into two groups. Group A (primary prevention group) included 27 patients, without a history of sustained ventricular arrhythmias or syncope, treated with ICDs because they were classified as high risk due to the presence of at least two of the following criteria: long history of disease defined as an interval longer than 4 years since diagnosis (n=23, 85.2%), left ventricular ejection fraction 30% (n=21, 77.7%), end-diastolic diameter 70 mm (n=20, 74.1%), non-sustained VT (n=15, 55.5%), family history of DC and sudden death (n=4, 14.8%).
Group B (secondary prevention group) included 27 patients treated with ICDs because of previous cardiac arrest due to VF (11 patients) or sustained VT (7 patients) or syncope presumed to be of arrhythmic origin because of VT/VF inducibility at electrophysiological evaluation (7 patients) or on a clinical basis (2 patients).
All patients gave written informed consent to ICD implantation.
Clinical, echocardiographic and Holter data of the two groups were compared at the date of implantation. The clinical outcome, the incidence of ICD shocks as well as antitachycardia pacing interventions were evaluated during follow-up in the two groups.
The different types of ICD implanted were: Ventak Mini II, AV II-IV, Prizm I-II, Vitality and Renewal I (Guidant), Contour II (Ventitrex-S. Jude), Belos (Biotronik), Defender II (Ela Medical), Jewel II and AT, Gem III, Insync and Marquis (Medtronic). Ten single chamber, 13 dual chamber and 4 ICDs with biventricular pacing capabilities were used in group A and 14 single chamber, 9 dual chamber and 2 ICDs with biventricular pacing capabilities were used in group B. All devices had EGM storage capabilities. Antitachycardia pacing was generally programmed for ventricular tachyarrhythmias in a range between 150–160 and 200–220 beats per minute (bpm). All arrhythmias with a rate > 200–220 bpm were considered as VF and treated only with shocks.
Statistical analysis
Differences among group means at baseline were compared by one-way analysis of variance. Differences among proportions were compared using the Chi-square test applying the Yates correction. The survivor functions from the time of ICD implantation were analysed using the Kaplan–Meier method and compared by Mantel Cox test.
For our statistical analysis, SPSS version 11.0 for Windows was used. Data were expressed as average ± standard deviation or as percentage. Results were regarded as statistically significant when P<0.05.
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Results |
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Baseline clinical data
Groups A and B had similar proportions of patients in NYHA class I–II (74% vs 78%, P=NS), mean left ventricular ejection fraction (25 ± 7% vs 28 ± 8%; P=NS) and left ventricular end-diastolic diameter (7.6 ± 1.1 vs 7.1 ± 1.1 cm; P=NS). The number of patients with spontaneous non-sustained VT and sustained VT/VF inducibility was also similar in the two groups (Table 1).
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The two groups differed in terms of age at implantation (46 ± 15 vs 59 ± 17 years in group A and B, respectively; P=0.008), ß-blocker treatment (89% vs 62%; P=0.02), interval since first symptom (107 ± 67 vs 53 ± 41 months; P=0.0007) and since diagnosis (86 ± 60 vs 40 ± 50 months; P=0.004) (Table 1). In group A, 11 patients underwent electrophysiological evaluation: sustained monomorphic VT was inducible in 2 patients (18%) and VF in 4 patients (36%). In group B, 16 patients underwent baseline electrophysiological evaluation: sustained monomorphic VT was inducible in 9 patients (56%) and VF in 6 patients (38%). In the 9 patients treated with ICD because of syncope, 7 underwent electrophysiological evaluation: in all of them sustained ventricular arrhythmias were inducible (4 VT, 3 VF).
Outcome
The follow-up after ICD implantation was longer in group B (33 ± 23 months) than in group A patients (21 ± 14 months, P=0.01) (Table 2). Three patients (11%) in group A and 5 patients (19%) in group B (P=NS) died during follow-up. Sudden death occurred in 1 patient (4%) in each group after an arrhythmic storm only initially responsive to ICD shocks; unfortunately, it was not possible to acquire their post-mortem ICD-EGMs.
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Two patients (7.4%) in group A and 4 patients (14.8%) in group B (P=NS) underwent heart transplantation respectively after 19 and 39 ± 12 months.
As shown in Table 3 and Fig. 1, the 12-month cumulative risks of appropriate ICD intervention were 41% in group A and 57% in group B (P=NS).
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During follow-up, 4 patients (15%) in group A only had interventions for VT (<220 bpm), 4 (15%) only interventions for VF, 3 (11%) for both. In group B, 6 patients (22%) only had interventions for VT, 1 (4%) only for VF, 10 (37%) for both.
In group A, the 17 patients showing the combination of left ventricular ejection fraction 30% and left ventricular end diastolic diameter 70 mm had a 12-month incidence of appropriate interventions significantly higher than the other 10 patients without these characteristics (68% vs 0%; P=0.01) (Fig. 2). The association of left ventricular ejection fraction 30% and history of non-sustained VT as well as left ventricular end-diastolic ventricular diameter 70 mm and non-sustained VT were not associated with a significantly higher proportion of appropriate interventions during follow-up.
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In group B, 7 of 9 patients (78%) with syncope had appropriate interventions (in 5 patients for VF or VT with rate >220 bpm) during follow-up.
The incidence of inappropriate shocks was 22% (6 patients) in group A and 19% (5 patients) in group B (P=NS). In group A, one patient received inappropriate shocks due to sinus tachycardia and the others due to atrial fibrillation (in three patients with fast ventricular response detected in the VF zone). In group B, one patient received inappropriate shocks due to sinus tachycardia and 4 patients due to atrial fibrillation.
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Discussion |
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Our study showed that patients with idiopathic DC treated with ICD for primary prevention because they were considered to be at high risk of sudden death on the basis of clinical criteria and patients treated with ICD for secondary prevention had a similar outcome and appropriate intervention rate (41% and 57% respectively; P=NS) during the year following implantation. All patients were on optimal medical treatment, included ß-blockers (metoprolol or carvedilol) at the highest dosage tolerated; nearly 50% of patients in the primary prevention group and 70% in the secondary prevention group were on amiodarone.
In patients with ischaemic heart disease, severe or moderate to severe left ventricular dysfunction [18], left ventricular dysfunction in conjunction with spontaneous non-sustained and inducible sustained ventricular arrhythmias identifies patients at higher risk of sudden death who can benefit from an ICD [19,20].
Most of these markers do not seem as useful in patients with DC. The Cardiomyopathy Trial [12] could not demonstrate that ICD reduced mortality in patients with DC, symptomatic heart failure and a left ventricular ejection fraction <30% as the only risk factors. However, the trial was not completed, as total mortality was much lower than expected and only 104 patients of the planned 1348 were enroled; for this reason the study could not reach any conclusion about the benefit of ICDs in DC. In addition, only patients with a recent diagnosis (<9 months) were included; the outcome of these patients is extremely unpredictable, as many can significantly improve in the following years on optimal medical treatment [21,22], also after exclusion of active myocarditis by endomyocardial biopsy. Moreover, in early onset DC the incidence of sudden death can be relatively low compared with the incidence of death due to pump failure [14].
Other authors have suggested that left ventricular dysfunction is not sufficient by itself to identify patients with DC at higher risk of sudden death. Grimm and others [15] identified the association of non-sustained VT with left ventricular ejection fraction <30% or with end-diastolic diameter >70 mm as predictors of sudden death. The same authors [16] showed that patients with a long history of disease, severe dysfunction and non-sustained VT had the same rate of appropriate ICD interventions as patients with DC and previous cardiac arrest or syncope of unknown origin during a follow-up of 36 months.
The recently published DEFINITE study confirmed that patients with spontaneous ventricular arrhythmias and left ventricular ejection fraction 35% had a significant reduction of SD (80%) if treated with an ICD [23]. Although not significant (probably because of the low number of events), total mortality reduction (34%) was similar to that found in the MADIT II trial (31%) [18].
In contrast to these data, the AMIOVIRT [13] showed that ICD implantation was not superior to amiodarone in 103 patients with an ejection fraction lower than 35% and non-sustained VT. Possible explanations could be the lower number of patients enroled in the AMIOVIRT and also that ICD was compared with amiodarone in this study.
However, it is likely that non-sustained VT has little adjunctive role in predicting sudden death in patients with DC, as suggested by several authors [24,25] and recently by our group in a larger population [26]. In the present experience the rate of ICD interventions was much higher in patients with both severe left ventricular dysfunction and dilatation rather than in patients with non-sustained VT. In addition, recent data from SCDHeFT seemed to confirm that, in a larger population of patients with heart failure and left ventricular ejection fraction 35%, ICDs could significantly reduce total mortality by 23% [27] independently of spontaneous arrhythmias, and this was also evident in patients with non-ischaemic cardiomyopathy.
In our study, another interesting point was the high rate of interventions for VT (treated with antitachycardia pacing in most cases), also if no patients had a history of sustained VT before implantation. In addition, few cases had inducible sustained ventricular arrhythmias at electrophysiological study but none of them had appropriate interventions for VT during follow-up.
The secondary prevention group also included patients with a history of syncope of unknown origin but presumably due to ventricular tachyarrhythmias [28,29]. It is well known that in this group the risk of sudden death is considerable [30] and the rate of appropriate ICD interventions high [16,29], regardless of electrophysiological results [31]. Also in our study the rate of interventions, especially for fast VT, was very high in this subgroup (78%).
Study limitations
This was a two-centre, observational, non-randomized study analysing the efficacy of ICDs in patients with DC. For secondary prevention we considered only patients with class I indications for ICD implant [11] and for primary prevention we identified patients at higher risk on the basis of previous published data [14,15].
The small size of the patient population was another limitation but at present no published studies on much larger populations are available. Furthermore, in other published or presented trials on primary prevention of sudden death [12,13,23,27], the patient population was selected on the basis of few variables with a low positive predictive value, such as left ventricular dysfunction and heart failure [27], left ventricular dysfunction in patients with recent onset DC [12] or moderate to severe left ventricular dysfunction and non sustained VT [13,23].
As in other studies [16], it has to be underlined that ICD interventions are not synonymous with aborted sudden death. However, 26% of patients in group A were treated for VF or sustained VT with rates higher than 220 bpm, a condition potentially life-threatening especially in patients with severe left ventricular impairment.
Clinical implications
This study is a preliminary observation on the potential benefit of ICDs for primary prevention in selected patients (i.e. long history of both severe left ventricular dysfunction and dilatation despite optimal medical treatment) considered at high risk of sudden death but otherwise with a good survival expectancy without heart transplantation. In addition, the study confirmed that ICDs can be considered to be a treatment option in patients with DC and syncope of unknown origin, because of the high proportion of major arrhythmic events in this population.
The CAT and AMIOVIRT failed to identify patients who could benefit from ICD treatment, probably because of the low number of patients enroled and the low risk of the population selected, rather than a real inefficacy of the treatment, confirmed by other more recent trials [23,27]. Our report underlines the need for careful patient selection; along these lines, it is likely that also other new parameters [32] will be useful.
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