ICDs have contributed to the reduction in ventricular fibrillation out of hospital cardiac arrests

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A study published ahead of print in Circulation shows that the use of implantable cardioverter defibrillators (ICDs) may be partly responsible for the reduction in the number of ventricular fibrillation out of hospital cardiac arrests.

Michiel Hulleman, Department of Cardiology, Academic Medical Center, University of Amsterdam, The Netherlands, and others wrote that the proportion of out-of-hospital cardiac arrests (OHCAs) with ventricular fibrillation recorded as the initial rhythm has declined from 54% to 38% over a 15-year period. They added that while the reason for this decline is not clear, the introduction of ICDs (the therapy became more common after supportive trial evidence was published in 1997) has been associated with it.

Using data from the ARREST (Amsterdam Resuscitation Studies) trial, Hulleman et al compared the incidence of ventricular fibrillation OHCAs in 1995–1997 with the incidence in 2005–2008. They also calculated the number of ventricular fibrillation OHCAs prevented by ICD shocks in 2005–2008 and compared this figure with the observed decrease in ventricular fibrillation OHCAs between 1995–1997 and 2005–2008.

They found that the proportion of patients with ventricular fibrillation OHCAs declined from 63% in 1995–1997 to 47% in 2005–2008 (p<0.001). The investigators also found that the use of an ICD prevented 81 cases of presumed ventricular fibrillation OHCAs in cohort of 166 patients with life-threatening arrhythmias, which they said amounted to an incidence of 1.2/100,000 person years (of prevented OHCAs) in North Holland in 2005–2008. Hulleman et al wrote: “As the ventricular fibrillation OHCA incidence declined by 3.6/100,000 [in North Holland] between 1995–1997 and 2005–2008, ICD usage thus accounted for 33% of the decline in ventricular fibrillation OCHA.”

The investigators stated that a previous study found that the use of an ICD resulted in an 10–33% reduction in the incidence of ventricular fibrillation OHCAs, but added that the authors of this study did not (as they did) account for the correction of multiple successful shocks or the less than 100% likelihood that a life-threatening arrhythmia triggered a resuscitation attempt.

According to Hulleman et al, other reasons aside from the use of ICD therapy may account for the reduction in ventricular fibrillation OHCAs. For example, they wrote: “In a retrospective cohort study, it was shown that OHCA victims taking beta-blockers were five times more likely to shown non ventricular fibrillation as the first documented rhythm.” They added that the reduction in ventricular fibrillation OHCAs may be more a reflection of faster deteriorating ventricular fibrillation to another rhythm (eg, asystole) rather than an actual reduction in the incidence of ventricular fibrillation, noting: “In situations in which the response time is extremely short, such as in airports or casinos equipped with automatic external debrillators, ventricular fibrillation is the presenting rhythm in a high proportion of cases.”

Concluding, the authors stated that while ICD therapy did contribute to the reduction in ventricular fibrillation OHCAs, “there must be other factors that at least equally contribute to the declined incidence.”

One of the investigators Rudolph W Koster, Department of Cardiology, Academic Medical Center, University of Amsterdam, The Netherlands, told Cardiac Rhythm News: “ICDs only explain less than half of the reduction in ventricular fibrillation OHCA. We have to identify the others causes, which account for more than half, of the decline. Ventricular fibrillation offers the best opportunity to save lives compared to any other rhythm.”

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