**2. Long-term benefit of ICD therapy**

#### **2.1. Secondary prevention trials**

Already in 1991, Tchou et al.[9] reported in a single center cohort of 184 patients who re‐ ceived an ICD between 1982 and 1989 (84% with ventricular fibrillation (VF) or sustained ventricular tachycardia (VT), 9% with non-sustained VT (NSVT) and 6% with pre-/syncope) that the actual risk of receiving an adequate shock by the fifth year after implantation was 69%, with an observed bimodal distribution: high within first year, and rise after four years. Occurrence of adequate ICD shock was defined as electrocardiographic documentation (ECG) of sustained VT at the time of shock or if it was preceded by sudden onset of severe presyncopal symptoms or syncope.

the shock. During a mean follow-up of 70 ± 51 months 53% of the patients received ade‐ quate ICD therapy, two thirds of them within the first year of implantation. Out of 127 pa‐ tients (16%) without adequate ICD therapy within 5 years following the index generator implantation, 8%, 20% and 24% of patients experienced adequate ICD therapy after 6, 10

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Data from another single center ICD registry were reported by Koller et al. in 2008.[13] This registry comprised data of 442 patients with predominantly secondary prevention (59%) with ischemic (76%) or dilated cardiomyopathy (24%) with a median follow-up of 3.6 years (max 12.7 years). Adequate ICD therapy of ventricular arrhythmias stored by intracardiace‐ lectrograms had to be confirmed by an experienced electrophysiologist. The cumulative inci‐ dence of any adequate ICD therapy was 52% during a 7-year observation period with a twofold higher risk for patients with secondary prevention compared to primary prevention. Patients without former adequate ICD therapy within 6 years after the first ICD implanta‐ tion had an observed risk of only 6% for adequate ICD intervention in the following 2 years.

The long-term follow-up of the Leiden Out-of-Hospital Cardiac Arrest Trial (LOHCAT)[14] was the first prospective single center observational study to assess the rate of mortality and risk of adequate ICD therapy in patients with secondary prevention. A total of 456 patients (86% males, mean LVEF 35±14%) with ischemic heart disease and secondary prevention in‐ dication were followed for 54±35 months after ICD implantation. Adequate ICD therapy was checked by printouts of the ICD memory. During follow-up 22% of the patients died. The cumulative incidence of adequate ICD therapy at 1, 5, and 8 years was 24, 52 and 61%, respectively. Independent factors for higher risk of adequate ICD intervention were previ‐ ous VT, history of AF, wide QRS and poor LVEF. No predictive factors for the absence of ventricular arrhythmia could be identified. Of the 456 patients, 167 (37%) outlived the lifespan of their index ICD and got generator replacement. No data were reported concerning how many of these patients had no former adequate ICD therapy and/or received the first

The INcidence free SUrvival after ICD Replacement (INSURE)[15] trial was the first pro‐ spective multicenter observational study to evaluate the risk of adequate ATP and/or ICD shock delivery after elective ICD replacement. A total of 510 unselected ICD-patients with (48%) and without (52%) former adequate ICD therapy were enrolled in 29 germancenters from 2002 until 2007 after an average life-span of their first ICD generator of 62±18 months. After device replacement patients were followed every 3 to 6 months (mean follow-up 22±16 months) until occurrence of an adequate ICD therapy (stored by intracardiacelectro‐ grams and confirmed by an adjudication committee consisting of three experienced electro‐ physiologists), death, second generator replacement or until common study termination endpoint. The vast majority (86%) of patients had initially been implanted for secondary prevention of SCD. The cumulative rates of adequate ICD interventions after one, two and three years following generator replacement were 32.4%, 41.3% and 48.1% in patients with former adequate ICD therapy and 10.6%, 17.6% and 21.4% in patients without former ade‐ quate ICD therapy, respectively (HR 3.08, CI: 2.15-4.39, p < 0.001) (Figure 2). In patients

and 15 years of follow-up, respectively.

Notably, only 35 patients (8%) had follow-up longer than 6 year.

adequate ICD Therapy after generator replacement.

Grimm et al.[10] investigated ICD therapy episodes which occurred for the first time in pa‐ tients who did not require such therapy prior to generator change. This was a prospective sin‐ gle center study enrolling 26 secondary prevention patients (77% with cardiac arrest and 23 with sustained VT) who received their second ICD device 30±9 months after initial ICD implan‐ tation. Notably, at that time patients had epicardial electrodes, and only a single patient had an ICD generator with the option to memorize endocardialelectrograms. Adequate shocks were defined as spontaneous ICD discharges preceded by severe symptoms like presyncope or syn‐ cope or documentation of VT/VF by Holter or telemetry monitoring or stored ECG by ICD. Dur‐ ing a mean follow-up period of 21±9 months after ICD generator replacement, ICD therapy was reported in 13 of 26 patients (50%), classified as adequate in 9 patients (35%).

Dürsch et al.[11] aimed to evaluate retrospectively the necessity of the replacement of ICD generators in patients without any adequate, spontaneous ventricular arrhythmia episode during the life-time of the first implanted device. This study, reported in 1998, compared 62 secondary prevention patients (mean follow-up 51 ± 14 months) with an elective generator replacement due to battery depletion with 151 ICD patients without replacement (follow-up 16.5 ± 11 months). There was a preponderance of male patients (>80%) with a mean left ven‐ tricular ejection fraction (LVEF) of 31% in both groups. In contrast to the study of Grimm et al. 86% of patients had transveonusendocardial ICD electrodes and 95% of devices (follow‐ ing generator exchange) had the option to memorize endocardial cardiograms. At that time most of the ICD systems had the capability of antitachycardiac pacing (ATP) prior to ICD shock delivery. For the total patient group there was a 5 year event-free probability of 23%, and no differences were found between the two groups. Subanalysis of the replacement group patients revealed no difference in the probability of adequate ICD therapy occurrence prior to or after the replacement of the pulse generator. Notably, in 6 of the 62 (10%) pa‐ tients, the first adequate ICD therapy was documented after generator replacement.

Tandri et al.[12] reported in 2006 a single center ICD registry of 1382 patients, who re‐ ceived their first ICD between 1980 and 2003 (76% men, LVEF 33 ± 11%) with mainly sec‐ ondary prevention indication (77%). In 787 (57%) of these patients ICD therapy informations were available. Adequate ICD therapy was determined based either on the ICD memory or for ICDs without ECG storage capability on the symptoms that preceded the shock. During a mean follow-up of 70 ± 51 months 53% of the patients received ade‐ quate ICD therapy, two thirds of them within the first year of implantation. Out of 127 pa‐ tients (16%) without adequate ICD therapy within 5 years following the index generator implantation, 8%, 20% and 24% of patients experienced adequate ICD therapy after 6, 10 and 15 years of follow-up, respectively.

**2. Long-term benefit of ICD therapy**

Already in 1991, Tchou et al.[9] reported in a single center cohort of 184 patients who re‐ ceived an ICD between 1982 and 1989 (84% with ventricular fibrillation (VF) or sustained ventricular tachycardia (VT), 9% with non-sustained VT (NSVT) and 6% with pre-/syncope) that the actual risk of receiving an adequate shock by the fifth year after implantation was 69%, with an observed bimodal distribution: high within first year, and rise after four years. Occurrence of adequate ICD shock was defined as electrocardiographic documentation (ECG) of sustained VT at the time of shock or if it was preceded by sudden onset of severe

Grimm et al.[10] investigated ICD therapy episodes which occurred for the first time in pa‐ tients who did not require such therapy prior to generator change. This was a prospective sin‐ gle center study enrolling 26 secondary prevention patients (77% with cardiac arrest and 23 with sustained VT) who received their second ICD device 30±9 months after initial ICD implan‐ tation. Notably, at that time patients had epicardial electrodes, and only a single patient had an ICD generator with the option to memorize endocardialelectrograms. Adequate shocks were defined as spontaneous ICD discharges preceded by severe symptoms like presyncope or syn‐ cope or documentation of VT/VF by Holter or telemetry monitoring or stored ECG by ICD. Dur‐ ing a mean follow-up period of 21±9 months after ICD generator replacement, ICD therapy was

Dürsch et al.[11] aimed to evaluate retrospectively the necessity of the replacement of ICD generators in patients without any adequate, spontaneous ventricular arrhythmia episode during the life-time of the first implanted device. This study, reported in 1998, compared 62 secondary prevention patients (mean follow-up 51 ± 14 months) with an elective generator replacement due to battery depletion with 151 ICD patients without replacement (follow-up 16.5 ± 11 months). There was a preponderance of male patients (>80%) with a mean left ven‐ tricular ejection fraction (LVEF) of 31% in both groups. In contrast to the study of Grimm et al. 86% of patients had transveonusendocardial ICD electrodes and 95% of devices (follow‐ ing generator exchange) had the option to memorize endocardial cardiograms. At that time most of the ICD systems had the capability of antitachycardiac pacing (ATP) prior to ICD shock delivery. For the total patient group there was a 5 year event-free probability of 23%, and no differences were found between the two groups. Subanalysis of the replacement group patients revealed no difference in the probability of adequate ICD therapy occurrence prior to or after the replacement of the pulse generator. Notably, in 6 of the 62 (10%) pa‐

tients, the first adequate ICD therapy was documented after generator replacement.

Tandri et al.[12] reported in 2006 a single center ICD registry of 1382 patients, who re‐ ceived their first ICD between 1980 and 2003 (76% men, LVEF 33 ± 11%) with mainly sec‐ ondary prevention indication (77%). In 787 (57%) of these patients ICD therapy informations were available. Adequate ICD therapy was determined based either on the ICD memory or for ICDs without ECG storage capability on the symptoms that preceded

reported in 13 of 26 patients (50%), classified as adequate in 9 patients (35%).

**2.1. Secondary prevention trials**

80 Cardiac Defibrillation

presyncopal symptoms or syncope.

Data from another single center ICD registry were reported by Koller et al. in 2008.[13] This registry comprised data of 442 patients with predominantly secondary prevention (59%) with ischemic (76%) or dilated cardiomyopathy (24%) with a median follow-up of 3.6 years (max 12.7 years). Adequate ICD therapy of ventricular arrhythmias stored by intracardiace‐ lectrograms had to be confirmed by an experienced electrophysiologist. The cumulative inci‐ dence of any adequate ICD therapy was 52% during a 7-year observation period with a twofold higher risk for patients with secondary prevention compared to primary prevention. Patients without former adequate ICD therapy within 6 years after the first ICD implanta‐ tion had an observed risk of only 6% for adequate ICD intervention in the following 2 years. Notably, only 35 patients (8%) had follow-up longer than 6 year.

The long-term follow-up of the Leiden Out-of-Hospital Cardiac Arrest Trial (LOHCAT)[14] was the first prospective single center observational study to assess the rate of mortality and risk of adequate ICD therapy in patients with secondary prevention. A total of 456 patients (86% males, mean LVEF 35±14%) with ischemic heart disease and secondary prevention in‐ dication were followed for 54±35 months after ICD implantation. Adequate ICD therapy was checked by printouts of the ICD memory. During follow-up 22% of the patients died. The cumulative incidence of adequate ICD therapy at 1, 5, and 8 years was 24, 52 and 61%, respectively. Independent factors for higher risk of adequate ICD intervention were previ‐ ous VT, history of AF, wide QRS and poor LVEF. No predictive factors for the absence of ventricular arrhythmia could be identified. Of the 456 patients, 167 (37%) outlived the lifespan of their index ICD and got generator replacement. No data were reported concerning how many of these patients had no former adequate ICD therapy and/or received the first adequate ICD Therapy after generator replacement.

The INcidence free SUrvival after ICD Replacement (INSURE)[15] trial was the first pro‐ spective multicenter observational study to evaluate the risk of adequate ATP and/or ICD shock delivery after elective ICD replacement. A total of 510 unselected ICD-patients with (48%) and without (52%) former adequate ICD therapy were enrolled in 29 germancenters from 2002 until 2007 after an average life-span of their first ICD generator of 62±18 months. After device replacement patients were followed every 3 to 6 months (mean follow-up 22±16 months) until occurrence of an adequate ICD therapy (stored by intracardiacelectro‐ grams and confirmed by an adjudication committee consisting of three experienced electro‐ physiologists), death, second generator replacement or until common study termination endpoint. The vast majority (86%) of patients had initially been implanted for secondary prevention of SCD. The cumulative rates of adequate ICD interventions after one, two and three years following generator replacement were 32.4%, 41.3% and 48.1% in patients with former adequate ICD therapy and 10.6%, 17.6% and 21.4% in patients without former ade‐ quate ICD therapy, respectively (HR 3.08, CI: 2.15-4.39, p < 0.001) (Figure 2). In patients without former adequate ICD interventions, only advanced NYHA stages were associated with higher risk of adequate ICD interventions. However, no predictive factors for lower probability of ICD therapy could be identified in this group.

**2.2. Primary prevention trials**

in both studies.

109 patients (10,7%) during the post-trial period.

**Author / Study Year N Age**

coronary artery disease.

The first trial which tried to provide data on the long-term benefit of ICD therapy in pri‐ mary prevention patients was published in 2008 by Alsheikh-Ali.[16] Patients with prior myocardial infarction and LVEF ≤35% who received ICD for primary prevention between 1995 and 2005 formed the basis of this retrospective single center analysis. Of 525 predomi‐ nantly male patients, 115 (22%) received adequate ICD therapy during a mean follow-up of 24 months. Patients who survived more than 5 years after ICD implantation without ade‐ quate therapy, the incidence of adequate ICD intervention was 6% after 7 years of follow-up. These observations were in accordance to the data of Koller et al. who reported the same incidence for patients with secondary prevention 7 years after ICD implantation. However, in both studies only 6-8% of patients had follow-up longer than 6 years after first ICD im‐ plantation. No predictive factors for a lower probability of ICD therapy could be identified

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The extended 8-year follow-up study of the Multicenter Automatic Defibrillator Implantation (MADIT) IITrial was published in 2010.[17] Post-trial mortality data for all study participants were obtained from the enrolling centers through hospital records and death registries from 2001 until 2009. One-thousand-twenty study patients who survived to trial closure of MADIT II formed the basis of this study. The primary endpoint was the occurrence of all-cause mortality during a median follow-up of 7.6 years. Patients who were treated with an ICD showed a signif‐ icant lower risk of death (34%) compared with non-ICD patients. The evident benefit of ICD therapy continued even in the long-term follow-up of up to 8 years, but only for patients with single chamber ICD. Patients with a dual chamber ICD (programmed to active DDD-pacing re‐ gardless of conduction abnormalities) and more advanced NYHA class (≥ II) at enrolment, ex‐ perienced a late increase in mortality due to unnecessary right ventricular pacing leading to progressive heart failure. This observation underlines previous reported data.[18] Regarding the long-term benefit due to adequate ICD therapy in the extended MADIT II trial, the cumula‐ tive probability of adequate ICD intervention during 8 years of follow-up was 68%. However, complete information of ICD interrogation during long term follow-up was only available in

**(mean y)**

**Table 3.** Baseline characteristics of patients in primary prevention trials with long-term follow-up

Alsheikh-Ali et al. 2008 525 67±11 81 23±7 100 - 100 Goldenberg et al. 2010 630 64±11 85 ≤35 100 - 100 Van Welsenes et al. 2011 1302 63±11 80 29±12 68 32 68 Van Welsenes et al. 2011 114 61±11 80 26±9 59 41 59

**LVEF**: left ventricular ejection fraction; **ICM**: ischemic cardiomyopathy; **NICM**: non-ischemic cardiomyopathy; **CAD**:

**Male (%)**

**LVEF (mean%)** **ICM (%)**

**NICM (%)**

**CAD (%)**


**LVEF**: left ventricular ejection fraction; **ICM**: ischemic cardiomyopathy; **NICM**: non-ischemic cardiomyopathy; **CAD**: coronary artery disease; **no HD**: no heart disease. **n.r**.: not reported

**Table 1.** Baseline characteristics of patients in secondary prevention trials with long-term follow-up


**Retro s.c.:** retrospective single center-study; **pros. s.c.:** prospective single center-study; **pros. m.c.:** prospective multicenter study; **FU:** follow-up; **y:** years.

**Table 2.** Incidence of adequate ICD therapy according to follow-up time in secondary prevention trials

#### **2.2. Primary prevention trials**

without former adequate ICD interventions, only advanced NYHA stages were associated with higher risk of adequate ICD interventions. However, no predictive factors for lower

> **Male (%)**

**LVEF**: left ventricular ejection fraction; **ICM**: ischemic cardiomyopathy; **NICM**: non-ischemic cardiomyopathy; **CAD**:

**FU after 1. ICD replacement (mean months)** **Overall FU (mean months)**

**Table 1.** Baseline characteristics of patients in secondary prevention trials with long-term follow-up

Tchou et al. retro. s.c. 24±19 - - 69% within 5y Grimm et al. pros. s.c. 30±9 21±19 - 35% within 6y Dürsch et al. retro. s.c. - - 50±14 77% within 5 y

Tandri et al. retro. s.c. 70±51 46±34 - 53% within 5 y

Koller et al. retro. s.c. - - 43 52% within 7 y Borleffs et al. pros. s.c. - - 54±35 61% within 8 y Van Welsenes et al. retro. s.c. 41±34 - - 51% within 5 y

**Table 2.** Incidence of adequate ICD therapy according to follow-up time in secondary prevention trials

Erkapic et al. pros. m.c. 62±18 22±16 - 21% within 3 y after ICD

**Retro s.c.:** retrospective single center-study; **pros. s.c.:** prospective single center-study; **pros. m.c.:** prospective multi-

**replacement (mean months)**

Tchou et al. 1991 184 61±11 81 37±14 n.r. 17 81 3 Grimm et al. 1993 26 56±15 73 38±15 n.r. 20 65 15 Dürsch et al. 1998 62 58±11 89 31±9 34 66 - Tandri et al. 2006 1382 62±11 76 33±11 72 28 70 - Koller et al. 2008 442 63 89 30 76 24 76 - Borleffs et al. 2008 456 65 86 35±14 100 - 100 - Van Welsenes et al. 2011 832 63±13 82 37±15 73 n.r. 73 n.r. Erkapic et al. 2012 510 65±10 83 39±16 37 25 71 38

**LVEF (mean%)** **ICM (%)**

**NICM (%)**

**CAD (%)**

**First adequate ICD therapy**

(thereof 10% after ICD

(additional 24% after ICD

replacement)

replacement)

replacement

**no HD (%)**

probability of ICD therapy could be identified in this group.

coronary artery disease; **no HD**: no heart disease. **n.r**.: not reported

**Author / Study Kind of study FU prior 1. ICD**

center study; **FU:** follow-up; **y:** years.

**(mean y)**

**Author / Study Year <sup>N</sup> Age**

82 Cardiac Defibrillation

The first trial which tried to provide data on the long-term benefit of ICD therapy in pri‐ mary prevention patients was published in 2008 by Alsheikh-Ali.[16] Patients with prior myocardial infarction and LVEF ≤35% who received ICD for primary prevention between 1995 and 2005 formed the basis of this retrospective single center analysis. Of 525 predomi‐ nantly male patients, 115 (22%) received adequate ICD therapy during a mean follow-up of 24 months. Patients who survived more than 5 years after ICD implantation without ade‐ quate therapy, the incidence of adequate ICD intervention was 6% after 7 years of follow-up. These observations were in accordance to the data of Koller et al. who reported the same incidence for patients with secondary prevention 7 years after ICD implantation. However, in both studies only 6-8% of patients had follow-up longer than 6 years after first ICD im‐ plantation. No predictive factors for a lower probability of ICD therapy could be identified in both studies.

The extended 8-year follow-up study of the Multicenter Automatic Defibrillator Implantation (MADIT) IITrial was published in 2010.[17] Post-trial mortality data for all study participants were obtained from the enrolling centers through hospital records and death registries from 2001 until 2009. One-thousand-twenty study patients who survived to trial closure of MADIT II formed the basis of this study. The primary endpoint was the occurrence of all-cause mortality during a median follow-up of 7.6 years. Patients who were treated with an ICD showed a signif‐ icant lower risk of death (34%) compared with non-ICD patients. The evident benefit of ICD therapy continued even in the long-term follow-up of up to 8 years, but only for patients with single chamber ICD. Patients with a dual chamber ICD (programmed to active DDD-pacing re‐ gardless of conduction abnormalities) and more advanced NYHA class (≥ II) at enrolment, ex‐ perienced a late increase in mortality due to unnecessary right ventricular pacing leading to progressive heart failure. This observation underlines previous reported data.[18] Regarding the long-term benefit due to adequate ICD therapy in the extended MADIT II trial, the cumula‐ tive probability of adequate ICD intervention during 8 years of follow-up was 68%. However, complete information of ICD interrogation during long term follow-up was only available in 109 patients (10,7%) during the post-trial period.


**LVEF**: left ventricular ejection fraction; **ICM**: ischemic cardiomyopathy; **NICM**: non-ischemic cardiomyopathy; **CAD**: coronary artery disease.

**Table 3.** Baseline characteristics of patients in primary prevention trials with long-term follow-up


**Table 4.** Incidence of adequate ICD therapy according to follow-up time in primary prevention trials

Van Welsenes et al. published two reports in 2011 on long-term follow-up data of a single center registry of patients with primary and secondary prevention. In the first publica‐ tion[19]they reported all-cause mortality and incidence of adequate ICD therapies in pa‐ tients with primary (61%) and secondary (39%) prevention during the lifetime of the first implanted ICD. The mean follow-up was 3.4±2.8 years. The cumulative 5-year incidence of mortality was 25% for primary and 23% for secondary prevention, without reaching statis‐ tifical significance between the two groups. The cumulative 5-year incidence of adequate ICD therapy (each episode had to be confirmed by a trained electrophysiologist by regard‐ ing the ICD memory/printouts) was 37% for primary and 51% for secondary prevention pa‐ tients (Figure 1).

**Figure 1.** Cumulative incidence of adequate ICD therapies prior elective generator replacement in patients with pri‐

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**Figure 2.** Cumulative incidence of first adequate ICD therapies (with confidence intervals) after elective device re‐

mary and secondary prevention

placement in patients with secondary prevention

The second puplication[20] comprised data of 114 patients with exclusively primary preven‐ tion who did not receive adequate therapy during the lifetime of their first ICD generator. The data were released from the same single center registry and were the first on the topic: "long-term benefit of ICD-therapy after elective device replacement in primary prevention patiens". The single center cohort consisted of mainly ischemic heart disease patients (80% male, mean age 61±11 years) with a mean LVEF of 26%. After an average life-span of their first ICD generator of 71±24 months the patients were followed after elective device replace‐ ment for 25±21 months. The cumulative event rate for adequate ICD intervention after re‐ placement increased continuously from 7% after one, 9% after two, to 14% after 3 years (Figure 3).

Long-Term Benefit and Challenges of Implantable Cardioverter Defibrillator Therapy http://dx.doi.org/10.5772/52325 85

**Author / Study Kind ofstudy FU prior 1. ICD**

84 Cardiac Defibrillation

tients (Figure 1).

(Figure 3).

**replacement (mean months)**

Alsheikh-Ali et al. retro. s.c. 24±0.4 - - 22% within 7y

Goldenberg et al. retro. m.c. 18 (10-30) n.r. 91 (42-108) 68% within 8y

Van Welsenes et al. retro. s.c. 41±34 - - 37% within 5 y

Van Welsenes et al. retro. s.c. 71±24 25±21 - 14% within 3 y

**Table 4.** Incidence of adequate ICD therapy according to follow-up time in primary prevention trials

**retros.c**.: retrospective single center-study; retro. **m.c.**: retrospective multi-center study; **FU:** follow-up; **y:** years.

Van Welsenes et al. published two reports in 2011 on long-term follow-up data of a single center registry of patients with primary and secondary prevention. In the first publica‐ tion[19]they reported all-cause mortality and incidence of adequate ICD therapies in pa‐ tients with primary (61%) and secondary (39%) prevention during the lifetime of the first implanted ICD. The mean follow-up was 3.4±2.8 years. The cumulative 5-year incidence of mortality was 25% for primary and 23% for secondary prevention, without reaching statis‐ tifical significance between the two groups. The cumulative 5-year incidence of adequate ICD therapy (each episode had to be confirmed by a trained electrophysiologist by regard‐ ing the ICD memory/printouts) was 37% for primary and 51% for secondary prevention pa‐

The second puplication[20] comprised data of 114 patients with exclusively primary preven‐ tion who did not receive adequate therapy during the lifetime of their first ICD generator. The data were released from the same single center registry and were the first on the topic: "long-term benefit of ICD-therapy after elective device replacement in primary prevention patiens". The single center cohort consisted of mainly ischemic heart disease patients (80% male, mean age 61±11 years) with a mean LVEF of 26%. After an average life-span of their first ICD generator of 71±24 months the patients were followed after elective device replace‐ ment for 25±21 months. The cumulative event rate for adequate ICD intervention after re‐ placement increased continuously from 7% after one, 9% after two, to 14% after 3 years

**FU after 1. ICD replacement (mean months)** **Overall FU (mean months)**

**First adequate ICD therapy**

after ICD replacement

**Figure 1.** Cumulative incidence of adequate ICD therapies prior elective generator replacement in patients with pri‐ mary and secondary prevention

**Figure 2.** Cumulative incidence of first adequate ICD therapies (with confidence intervals) after elective device re‐ placement in patients with secondary prevention

With the introduction of leads with multilumen design in 1997, lead survival curves initially improved but were still limited due to missing long-lasting insulation material. Silicon which is most often used for lead insulation has a good biocompatibility and flexibility, has a high friction resistance but prone to abrasion of lead insulation material. Even today in a certain type of ICD lead (RIATA®, SJM, Sylmar, CA) with silicon insulation (removed 2010 from distribution), time-dependent incidence of lead failure of 8-33% were reported.[21-24] The same lead model with a silicone-polyurethane copolymer (Optim™, SJM, Sylmar, CA) showed no increased incidence of lead failure, suggesting a better abrasion resistance.[22,25]

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Apart from lead insulation material, very small diameter of the ICD lead seemed to be a fur‐ ther risk factor of lead failure.[26] The 6.6 Sprint fidelis® lead (Medtronic, Inc., Minneapolis, MN) is prone to increased chance of lead fracture due to most likely less stress resistance. In 2008 this high-voltage ICD-lead was removed from the market. Actually, incidence of lead failure of 17% at 5 years of follow-up is reported for this lead.[27] Therefore, implanted Sprint fidelis and several Riata lead models should be carefully examined at the time of gen‐

Inadequate ICD therapy is a significant clinical issue. In literature it`s reported that 12-30% of ICD patients receive inadequate ICD therapies, mainly caused by supraventricular tachy‐ cardias, T-wave oversensing and lead failure.[28-30] Such unnecessary ICD therapies are as‐ sociated with increase of posttraumatic disorders as depression and anxiety.[31]It is still a matter of debate, if aside of morbidity, inadequate ICD shocks also have worse impact on the outcome of ICD patients.[30,32] However, it is our firm conviction, that the number of unnecessary ICD therapies triggered by SVTs can be considerably reduced by adequate ICD programming by an experienced physician. Furthermore, newer ICD algorithms reduced in‐ adequate ICD therapy triggered by T-wave oversensing by 97% while maintaining 100% sensitivity for detection of true ventricular arrhythmia.[33]The safety, efficacy and perform‐ ance of further new ICD discrimination algorithms is actually evaluated in a prospective

Since the introduction of the Lead Integrity Alert™ (LIA) by Medtronic in 2008, inadequate ICD therapies decreased by up to 50% in patients with fractured Sprint fidelis leads.[35,36] Moreover, it has been reported that this algorithm has the potential to early detect lead fail‐

Device replacement is associated with significant morbidity and some mortality. Data from a multicenter prospective registry of 1081 ICD patients who underwent device replacement (79% males, mean age 64±13 years) showed a complication rate of 4.3%. Major complications were observed in 2,6%, mostly infections or lead revisions. On multivariate analysis the presence of advanced Canadian Cardiovascular Society angina class (CCS ≥2), advanced NYHA stages (≥III), complex device systems (especially cardiac resynchronization systems),

erator replacement.

multi-center trial.[34]

ure of the affected Riata family®.[37]

**3.3. Risk of ICD generator replacement**

**3.2. Inadequate ICD therapy**

**Figure 3.** Cumulative incidence of first adequate ICD therapies after elective device replacement in patients with pri‐ mary prevention without prior adequate ICD therapy
