Methods

The EFFORTLESS S-ICD Registry is an international, observational, prospective, nonrandomized, standard of care evaluation that includes both retrospective and prospective patients. However, the QoL substudy was designed to include only prospective and first-time implant patients that were recruited from 29 sites in the Czech Republic, Denmark, Germany, Italy, the Netherlands, New Zealand, Portugal, and the United Kingdom from the period of March 2011 to July 2014. Patients were eligible for inclusion if they were implanted with a first generation S-ICD system per local clinical guidelines due to a primary or secondary prevention indication and were willing to participate and provide written informed consent. Patients were excluded, if they participated in another study that was considered to interfere with interpretation of the results from the EFFORTLESS S-ICD Registry, had previously been implanted with an ICD, experienced incessant VT and/or spontaneous, frequently recurring VT that could reliably be terminated with antitachycardia pacing, and if they had a bradycardia indication or cardiac resynchronization therapy.

The QoL substudy of the EFFORTLESS S-ICD Registry was designed to use the Mood and personality as precipitants of arrhythmia in patients with an Implantable cardioverter Defibrillator: A prospective Study (MIDAS) cohort as an unrelated comparison group. MIDAS is a prospective observational study before the S-ICD era that recruited consecutively implanted patients with a first-time TV-ICD system from August 2003 to February 2010 at the Erasmus Medical Center, Rotterdam, the Netherlands.

At each participating center, a member of staff approached patients for study participation at the time when patients were scheduled for the S-ICD implantation. All patients received oral and written information about the study. If willing to participate, they provided written informed consent. Patients would receive a reminder questionnaire if they did not return the first questionnaire. Similarly to the procedure in EFFORTLESS, patients from the MIDAS cohort were approached by a cardiologist or nurse about study participation. All patients received oral and written information about the study and signed an informed consent form if they were willing to participate.

The protocol for the EFFORTLESS S-ICD Registry was approved by the relevant medical ethics committees in each participating country. The registry was conducted according to the Declaration of Helsinki and ISO 14155:2009 and registered on http://www.ClinicalTrials.gov ( NCT01085435 ). The protocol for the MIDAS cohort was approved by the Medical Ethics Committee of the Erasmus Medical Center, Rotterdam, the Netherlands (MEC # 231.491/2003/148 – September 9, 2003).

Information on clinical and demographic variables captured from the patients’ medical records was entered into an online case record form. As information on particular demographic variables, such as education, marital status, participation in cardiac rehabilitation, and treatment for psychological problems are not entered standardly in patients’ medical records, these were included as purpose-designed questions in the questionnaire package containing the standardized and validated measures.

QoL was assessed with the standardized and validated 12-Item Short-Form Health Survey (SF-12) at baseline, 3, and 6, months after implant. The 12 items contribute to a Physical Component Summary and a Mental Component Summary score, with a range from 0 and 100 (0 = poorest possible QoL; 100 = best possible QoL). Both the Physical Component Summary and Mental Component Summary scores combine the 12 items in such a way that they compare to a national norm with a mean score of 50.0 and a standard deviation of 10.0.

To control for the potentially confounding influence of personality on QoL, patients completed the Type D Scale (DS14) at baseline. The DS14 is a 14-item measure tapping into negative affectivity (e.g., “I often feel unhappy”) and social inhibition (e.g., “I am a closed kind of person”). Items are rated on a 5-point Likert scale from 0 to 4 (score range for both subscales is 28), with a score of ≥10 on both traits indicating a Type D personality. The DS14 is a valid and internally consistent measure (Cronbach’s alpha: 0.80 for negative affectivity and 0.86 for social inhibition). Type D personality is a vulnerability factor for poorer QoL, life-threatening arrhythmias, and premature mortality in patients with an ICD.

Before propensity score matching, patients from the MIDAS cohort who had an indication for bradycardia or cardiac resynchronization therapy or with a secondary prevention indication due to monomorphic VTs were excluded from analyses, as these patients are not eligible for an S-ICD system. EFFORTLESS and MIDAS patients were matched 1:1 using propensity score matching on the following a priori selected variables: gender, age, indication for ICD (primary vs secondary), ischemic versus nonischemic etiology, and baseline physical QoL and mental QoL. Propensity score matching was performed using the greedy matching algorithm with the recommended caliper width by Austin. Multivariable modeling with repeated measures was used to analyze physical QoL and mental QoL at, baseline, 3, and 6 months after implantation. The time by ICD system (S-ICD vs TV) interaction was also considered in the multivariable modeling, if statistically significant at the 0.05 level. In a first model, a priori based on the literature, we choose to adjust for the following factors that might serve as potential confounders on QoL in multivariable analysis: low education, New York Heart Association (NYHA) functional class III to IV, amiodarone, cardiac rehabilitation attendance, treatment for psychological problems, Type D personality, and shocks during the 6-month follow-up period. In a second model, we adjusted additionally for all baseline factors that were significantly different between the EFFORTLESS and MIDAS cohorts despite matching. Data were analyzed using SAS version 9.2.

Results

Of the 419 EFFORTLESS patients prospectively enrolled, 95% (397 of 419) consented to participate. Of these patients, 17% (68 of 397) were excluded due to previous implantation with a TV-ICD system or pacemaker, whereas 20% patients (80 of 397) were excluded due to insufficient QoL data. After matching EFFORTLESS patients with patients from the MIDAS cohort using propensity score matching, data from 167 patients with an S-ICD and 167 patients with a TV-ICD system were used for analyses. A flowchart of the patient selection is shown in Figure 1 .

Flowchart of patient selection. ^# If patients had had a prior TV-ICD pacemaker implanted. *If pacemaker dependent, ICD with cardiac resynchronization therapy (CRT-D), or secondary prevention indication due to monomorphic ventricular tachyarrhythmias, as these patients are not eligible for an S-ICD system.

Baseline characteristics of the 2 cohorts are presented in Table 1 . Despite propensity score matching on a priori selected variables, the EFFORTLESS and MIDAS cohorts differed on some baseline characteristics. EFFORTLESS patients were less likely to have ventricular fibrillation as index arrhythmia, to be prescribed statins and diuretics, but more likely to have a lower QRS duration compared with the MIDAS patients. EFFORTLESS patients were more likely to have VT as index arrhythmia and to have diabetes and heart failure than MIDAS patients. There were no systematic differences on any of the other characteristics, including personality and baseline QoL (the latter was one of the matching criteria).

During the 6-month follow-up period, in the matched cohort of equal size (n = 167) and equal follow-up (6 months), 19 episodes were treated with a shock in the EFFORTLESS cohort compared with 29 in the MIDAS cohort.

Multivariable modeling examining the effect of ICD system, time, and ICD system by time interaction showed that the interaction was neither statistically significant for physical QoL (p = 0.0503) nor mental QoL (p = 0.3772), indicating that the evolution in QoL scores during the 6 months of follow-up was similar in patients with either an S-ICD or a TV-ICD system.

Therefore, analyses were run again including only the main effects for ICD system and time. These unadjusted analyses (without the interaction effect) showed no statistically significant main effects for ICD system (S-ICD vs TV) neither on physical (p = 0.1707) nor on mental QoL (p = 0.3364) across baseline, 3, and 6 months after implantation. When adjusting for a priori determined potential confounders (i.e., low education, NYHA functional class III-IV, amiodarone, cardiac rehabilitation attendance, treatment for psychological problems, Type D personality, and shocks during the 6-month follow-up period), the model estimate when comparing the 2 cohorts was statistically significant for physical QoL (p = 0.0324) but not for mental QoL (p = 0.2232; Table 2 , model 1). The mean score differences on physical and mental QoL between the 2 cohorts were largest at baseline with 2.32 (on a scale from 0 to 100) with the MIDAS cohort experiencing a slightly better QoL. For mental QoL, the same pattern was seen although the highest mean score difference between the 2 cohorts was at 6 months with a mean score difference of 1.26 (on a scale from 0 to 100). When adding also differences between the 2 cohorts on baseline characteristics to the variables entered in model 1, the largest mean difference between the 2 cohorts was reduced to 0.29 for physical QoL and to 0.14 for mental QoL ( Table 2 , model 2). Neither the model estimate for differences in physical (p = 0.8157) nor mental QoL (p = 0.9080) between the 2 cohorts was statistically significant. Shocks during follow-up were neither associated with physical QoL (p = 0.5648) nor mental QoL (p = 0.5161) in model 2, which was fully adjusted.

Table 2

Physical and mental quality of life of patients with an S-ICD system versus a TV-ICD system during the course of 6 months follow-up after implant

	EFFORTLESS (S-ICD system)	MIDAS (TV-ICD system)	p-value
	Mean [95% CI]	Mean [95% CI]
Model 1 ∗
Physical QoL (PCS)
Baseline	39.35 [37.75-40.95]	41.61 [40.02-43.19]	0.032
3 months	42.42 [40.87-43.98]	44.68 [43.15-46.21]
6 months	42.33 [40.72-43.93]	44.58 [43.00-46.17]
Mental QoL (MCS)
Baseline	41.60 [40.00-43.19]	42.84 [41.27-44.42]	0.2232
3 months	45.12 [43.53-46.71]	46.37 [44.80-47.93]
6 months	44.52 [42.85-46.20]	45.78 [44.12-47.41]
Model 2 †
Physical QoL (PCS)
Baseline	40.48 [38.69-42.27]	40.77 [39.12-42.42]	0.8157
3 months	43.56 [41.79-45.34]	43.85 [42.22-45.48]
6 months	43.45 [41.63-45.26]	43.74 [42.06-45.41]
Mental QoL (MSC)
Baseline	42.39 [40.60-44.19]	42.25 [40.59-43.92]	0.9080
3 months	45.86 [44.04-47.68]	45.72 [44.04-47.40]
6 months	45.19 [43.29-47.09]	45.05 [43.28-46.81]

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