Editor's Note: This Article of the Month is based on Hulleman M, Berdowski J, de Groot JR, et al. Implantable Cardioverter-Defibrillators Have Reduced the Incidence of Resuscitation for Out of Hospital Cardiac Arrest Caused by Lethal Arrhythmias. Circulation 2012;126:815-21.

Summary

Over the past twenty years, there has been a steady decline in the incidence and mortality from out of hospital ventricular fibrillation (VF). Much of this has been cautiously attributed to primary prevention defibrillator therapy. Despite robust clinical trial evidence, skepticism remains regarding the efficacy and cost-effectiveness of primary prevention ICDs. This study aims to understand the temporal relationship between rapid expansion of primary prevention ICD use and the concomitant decline in ventricular fibrillation rates.

Methods

Comparative analysis of a prospective database in North Holland in the Netherlands was used to compare out of hospital cardiac arrest (OHCA) between 1995-1997 and 2005-2008. Additionally, all ICD interrogations from all ICD patients in North Holland were collected and all appropriate shocks were identified. These two populations were considered (OHCA vs. ICD shocks) and analysis of the contribution of ICD therapy to the decline in OHCA due to ventricular fibrillation was attempted. Patients were excluded for monomorphic ventricular tachycardia (VT) outside of the VF zone on device programming, inability to obtain ICD electrograms (EGM), or shocks which were inappropriate (total 153 exclusions out of 1972 patients; ~8%). Corrections were made for multiple ICD shocks. The percentage of appropriate shocks that would have led to resuscitation attempts was determined by multiplying the number of life-threatening arrhythmias that were successfully terminated by ICD shocks by the probability that the life-threatening arrhythmia would have led to an EMS call and a subsequent OHCA attempt, based on prior literature. Life-threatening arrhythmia was defined as VF or polymorphic ventricular tachycardia, regardless of cycle length, or monomorphic VT faster than the lower limit of the programmed VF zone.

Results

In 1995-1997, 581 patients had OHCA- VF (21.1/100,000 patient years) compared to 2005-2008, in which 1173 people had OHCA- VF (17.4/100,000 patient years). The comparative rates of OHCA due to VF declined by 3.6/100,000 patient years (p<0.001). During the same time periods, the non-VF OHCA rates increased with a significant decline in the percentage contribution of ventricular fibrillation to total OHCA (63%-->47%, p<0.001).

Between 2005-2008, 3696 dispatches of emergency medical services (EMS) occurred- resuscitation was not attempted in 33% as the patient was considered dead on arrival. Among resuscitation efforts, 60% underwent bystander CPR (increase from 54% in prior time period), The time of initial call to initial rhythm assessment increased from 9 minutes to 10.5 minutes (p<0.001) while the time of initial call to shock decreased from 11 minutes to 10.7 minutes (p<0.001). During the time period 2005-2008, 21% of all EMS calls had an AED connected. Survival of all patients with OHCA increased from 9% to 14% (p<0.001); survival from VF OHCA increased from 17% to 31% (p<0.001).

In the ICD cohort, 1819 patients were analyzed, with 977 shocks delivered to 303 patients. Three hundred seventy one shocks were deemed inappropriate (predominantly due to SVT- 272 shocks, 28%); 135 shocks did not have EGMs available (excluded), and 132 shocks were excluded as monomorphic VT below the VF zone of the device.

The remaining episodes amounted to 339 shocks/166 patients. Seventy-six patients received multiple shocks. Using assumptions derived from the ARREST database, 194 instances of life-threatening arrhythmia in 166 patients led to aborted sudden cardiac arrest. Given that 62% of these would have led to an EMS call- ICD therapy was presumed to have prevented 81 cases of VF OHCA, amounting to 1.2/100,000 patient years. This accounts for 33% of the observed reduction of VF OHCA.

Conclusion

The incidence of out of hospital cardiac arrest due to ventricular fibrillation has decreased and this is in part due to the implementation of primary prevention ICD therapy. Conservative estimates suggest that ICD therapy accounts for 33% of the observed reduction in VF OHCA.

Perspective

Since the advent of the major primary prevention ICD trials, adoption of therapy remains tenuous due to concerns about the "real-life" applicability of ICD therapy.^1-3 While long-term data of the MADIT, and SCD-HeFT populations remain robust in the illustration of sudden death reductions, a vertically integrated analysis of a large community cohort of all out of hospital arrest had remained elusive.^4-6 The authors have assembled a comprehensive study of out of hospital cardiac arrest-inclusive of both arrhythmic and non-arrhythmic etiologies. Coupled with a comprehensive analysis of EMS calls within the ARREST database in Northern Holland, this study is to date the best analysis of the impact of ICD therapy on VF OHCA. While ICD shocks are not a surrogate for arrhythmic death in a 1:1 fashion, the authors conservatively estimate the contribution of their benefit.⁷ While not "perfect", this analysis suggests that not only is there a durable mortality benefit of ICD therapy for the individual that has been demonstrated in the MADIT II and SCD-HeFT populations at long-term follow up, but that primary prevention ICDs have impacted the public health as well.

Additionally, this data also highlights our need for further education and promotion of basic bystander resuscitation and AED use, as well as the need for risk stratification for sudden cardiac death, as the majority of sudden deaths occur in individuals not recognized as at-risk based on current protocols.⁸ These results should reaffirm our commitment to the prevention of sudden cardiac arrest in our patients and the manner in which we advocate for them.

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References

1. A comparison of antiarrhythmic-drug therapy with implantable defibrillators in patients resuscitated from near-fatal ventricular arrhythmias. The Antiarrhythmics versus Implantable Defibrillators (AVID) Investigators. N. Engl J Med 1997; 337: 1576-1583
2. Buxton, AR, Lee, KL, Fisher JD, Josephson ME, Prystowsky EN, Hafley G. A randomized study of the prevention of sudden death in patients with coronary artery disease. Multicenter Unsustained Tachycardia Trial Investigators. N Engl J Med 1999;341:1882-1890
3. Moss AJ, Hall WJ, Cannom DF, et al. Improved survival with an implanted defibrillator in patients with coronary disease at high risk for ventricular arrhythmia. Multicenter Automatic Defibrillator Implantation Trial Investigators. N Engl J Med 1996; 335:1933-1940
4. Goldenberg, I, Gillespie J, Moss AJ, et al. Long-term benefit of primary prevention with an implantable Cardioverter-defibrillator: an extended 8-year follow-up study of the Multicenter Automatic Defibrillator Implantation Trial II. Circulation 2010; 122: 1265-71.
5. Bardy G, Lee K, Mark D, et al. Long-term follow-up in the Sudden Cardiac Death Heart Failure Trial (SCD-HeFT). Heart Rhythm 2012; 9:1579
6. Bunch, TJ, White RD, Friedman PA, Kottke, TE, Wu LA, Packer DL. Trends in treated ventricular fibrillation out-of-hospital cardiac arrest: a 17-year population-based study. Heart Rhythm 2004; 1:255-259.
7. Ellenbogen KA, Levine JH, Berger RD, et al. Are implantable Cardioverter defibrillator shocks a surrogate for sudden cardiac death in patients with nonischemic cardiomyopathy? Circulation 2006; 113:776-782.
8. Myerburg RJ, Kessler KM, Castellanos A. Sudden cardiac death: epidemiology, transient risk, and intervention assessment. Ann Intern Med 1993;119:1187–1197.

Keywords: Defibrillators, Implantable, Incidence, Primary Prevention, Ventricular Fibrillation

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