Defibrillator shocks, their impact on quality of life and prognosis
Impact of defibrillator shocks on quality of life
From all the studies presented earlier, it is clear that ICD therapy prevents sudden cardiac death. However, ICD shocks can be painful and have been shown to affect the quality of life in both primary and secondary prevention trials. Patients with ICD can receive inappropriate shocks due to atrial fibrillation (AF), supraventricular tachycardia (SVT) or inappropriate sensing from the device. The quality of life (QOL) was assessed in the AVID trial as a secondary endpoint using the Medical Outcomes Short Form 36 item questionnaire (SF-36). Of the 905 patients enrolled in QOL analysis, 800 survived for longer than 1 year. Both treatment groups (ICD group versus antiarrhythmic group) had significant impairment in both physical functioning and mental well-being(Schron et al. 2002). ICD shocks were independently associated with reduction in both physical functioning and mental well-being. The CIDS trial also measured QOL, in the 400 patients who survived for > 1 year, patients assigned to the ICD group had an improvement in their quality of life scores compared to patients assigned to amiodarone. However, patients having frequent shocks (>5 shocks) had reduced QOL.
The SCD-HeFT trial also collected data on the quality of life using two different scales: The Duke Activity Scale Index (DASI) reflecting the overall physical functioning and the SF-36 Mental Health Inventory 5 which measures psychological well being (Mark et al. 2008). Data were collected at baseline, 3, 12 and 30 months of follow up. A total of 2479 patients (98%) enrolled in SCD-HeFT completed the quality of life portion of the study. Patients receiving ICD therapy and patients assigned to placebo had similar DASI scores and SF-36 MHI 5 scores at baseline. The psychological well being of patients receiving an ICD was significantly better at 3 months and 12 months compared to patients receiving placebo. There was no difference in the physical functioning at baseline or at 3, 12 or 30 months in the ICD group versus the placebo group. The quality of life of patients who received an ICD shock a month before the screening was significantly worse in multiple aspects (physical, psychological, social and self related health).
Impact of defibrillator shocks on prognosis
The SCD-HeFT Trial also evaluated the prognostic impact of ICD shocks in patients with ischemic and non-ischemic cardiomyopathy. Most of the patients received a single chamber ICD programmed to shock only therapy with no antitachycardia pacing involved. (Poole et al. 2008). Patients (n=811) were followed for 45.5 months and a third of patients (n=269) received ICD shocks. Patients who received appropriate ICD shock (n=128) were at increased risk of death (HR 5.68, 95% CI of 3.97 to 8.12, p < 0.001) compared to patients with no appropriate shocks. Patients who received inappropriate shocks were also at increased risk of death (HR 1.98, 95% CI of 1.29 to 3.05, p=0.002) compared to patients with no inappropriate shocks. Atrial fibrillation was the most common reason for inappropriate ICD shocks and the most common cause of death in patients receiving any shock was progressive heart failure.
Inappropriate shocks were examined in the MADIT-II trial. Of the 719 patients who received an ICD, inappropriate shocks occurred in 83 patients (11.5%). Inappropriate shocks represented a third (31.2%) of total shocks (Daubert et al. 2008). Independent predictors of inappropriate shocks included atrial fibrillation (HR = 2.9, P<0.01), smoking (HR 2.18, P=0.03), diastolic blood pressure of > 80 mmHg (HR = 1.61, P= 0.04) and antecedent appropriate shocks (HR = 2.25, P= 0.03). Again, inappropriate shocks were most likely due to AF (44%), SVT (36%) or abnormal sensing (20%). Implantation of a dual chamber ICD did not decrease the rate of inappropriate shocks compared to single chamber ICD implantation (38.6% versus 44% respectively, p=0.31). Any shock whether appropriate or inappropriate was associated with significant increase in mortality (HR 4.08, p<0.01). Inappropriate shocks were associated with a 2 fold increase in mortality (HR is 2.29, p=0.03) while appropriate shocks had a 3 fold increase in mortality (HR 3.36, p<0.01). Electrical instability in the form of VT or VF or atrial fibrillation could be markers of deteriorating heart function and pump failure(Obadah Al Chekakie 2009). It is unclear if the VT or VF that the patient experiences heralds progressive pump failure, or whether the fact that shocks my increase mortality due to their negative effect on contractility in this high risk population or if both assumptions are true.
Device programming studies: Safety, effectiveness and impact on quality of life
Since Shocks are associated with lower quality of life and increase mortality, attempts at reducing shocks (both appropriate and inappropriate) became the focus of several studies. Antitachycardia pacing (ATP) has been shown to terminate 78 to 94% of slow VTs (188 bpm) (Peinado et al. 1998). The PAINFREE RX II trial randomized 634 patients with ICDs to standardized ATP (n=313 patients) versus shocks (n=321 patients). The programming in the Standarized ATP arm included two main parameters: First programming ATP in the fast VT zone of 188 to 250 bpm, at 8 pulses and 88% of VT cycle length. Second is extending the detection to 18 of 24 beats to avoid shocking ventricular tachycardia that was going to terminate anyway. The primary objective was to demonstrate that ATP will not prolong treatment > 6 seconds compared to the shock arm. Secondary objectives included the QOL, ATP efficacy and acceleration and syncope (Sweeney et al. 2005). After mean follow up of 11+/- 3 months, 4230 ICD counters were retrieved, and electrograms were only available in 1827 episodes. A third of the shocks was deemed inappropriate and due to SVT and 0.2% were due to noise. Only 73% of total shocks were due to true ventricular arrhythmias. Of these, 431 (58%) were detected as VT, 32% as Fast VT and 10% as VF. ATP was successful as initial therapy in 81% of the episodes and failed in 54 episodes, of which 49 episodes were shocked while 5 were terminated by a second ATP therapy. ATP did not prolong therapy duration (median duration was 10 seconds in the ATP arm versus 9.7 seconds in the shock arm) and there was no significant difference in the acceleration of VT/VF between the two arms. Syncope was very rare in the two arms (2 in the ATP group and 1 in the shock arm) and the first shock success was identical between the two arms. There was no difference between the two groups at baseline in the QOL scores as assessed by the SF-36. Patients assigned to the shock arm had an improvement in the bodily pain scores at 12 months but no change in the other SF-36 subscales. While patients assigned to the ATP arm had significant improvement in 5 subscales (bodily pain, social functioning, role emotional, physical functioning and role physical). This trial established the safety and efficacy of ATP in the fast VT zone and the safety of extending the detection duration to 18 out of 24 beats, which led to a decrease in shocks (The patients assigned to the shock arm had 147 detected FVT episodes with only 99 episodes receiving therapy). This will be an important factor in the design and implementation of the PREPARE study.
The Primary Prevention Parameters Evaluation Study (PREPARE) study compared 700 patients who had received an ICD or Biventricular defibrillator for primary prevention within 6 months of enrollment (Wilkoff et al. 2008). The control group for the ICD patients was taken from the EMPIRIC trial while the control group for the Biventricular ICD (BiV ICD) arm was from the MIRACLE ICD trial. The cohort of the PREPARE study had the following programming parameters: Initial detection for VT at rate of >182 bpm, with ATP programmed to fast VT of 182 to 250 bpm, with detection prolonged to 30 of the 40 intervals to avoid shocking VT that was going to terminate anyway, programming SVT discriminators to arrhythmias < 200 bpm to prevent inappropriate shocks. The primary endpoint of the study was the morbidity index defined as 1) device related cardioversion or defibrillation whether appropriate or inappropriate, 2) syncope secondary to arrhythmia or presumed arrhythmia and 3) untreated sustained symptomatic VT/VF events. The PREPARE study patients were less likely to receive a shock for any cause in the first year as compared to the control cohort (8.5 % vs 16.9%, p<0.01) and were also less likely to receive inappropriate shocks even after correcting for differences in baseline variables including mean LVEF, hypertension, history of ischemic heart disease, syncope and baseline use of beta blockers. The morbidity index incidence density was significantly lower in the PREPARE cohort compared to the control cohorts (HR 0.26 versus 0.69, 95% CI of 0.2 to 0.72, p=0.003). Importantly, only 12 of the 40 syncope episodes were judged to be due to arrhythmia, and of those, only 11 were due to PREPARE programming. The PREPARE study established the efficacy of empirically programming the ICD detection and therapy to minimize both appropriate and inappropriate shocks. This is true for patients receiving ICD therapy for primary prevention only.
In summary: ICD therapy prevents sudden cardiac death but patients who receive an ICD shock have increased morbidity and mortality and poor quality of life. Programming the device can help minimize ICD shocks, whether appropriate or inappropriate. Patients with ICD therapy who receive a shock should be followed closely since they are at increased risk of pump failure.
Conclusion
Implantable cardioverter defibrillator therapy is important in sudden cardiac death prevention in patients with ischemic and non-ischemic cardiomyopathy as well as survivors of cardiac arrest. Cardiac resynchronization therapy with and without an ICD improves the quality of life and leads to reverse remodeling and independently prevents sudden cardiac death in patients with QRS > 120 msec and LVEF < 35% who are on optimal medical therapy. Defibrillator shocks are associated with adverse outcomes and pump failure. Careful patient selection and sophisticated programming can help prevent sudden cardiac death without compromising the quality of life of the patients.
