Letters to the Editor

An alternative estimate of the disappearance rate of ventricular fibrillation in out-of-hospital cardiac arrest in Sweden

Cardiac arrest is defined as the termination of cardiac activity associated with loss of consciousness, of spontaneous breathing, and of circulation. Sudden cardiac arrest and sudden cardiac death (SCD) are terms often used interchangeably. Most patients with out-of-hospital cardiac arrest have shown coronary artery disease or symptoms during the hour before the event. Cardiac arrest is potentially reversible by cardiopulmonary resuscitation, defibrillation, cardioversion, cardiac pacing, or treatments targeted at the underlying disease (e.g., acute coronary occlusion). We restrict SCD hereafter to cardiac arrest due to ventricular fibrillation, including rhythms shockable by an automatic external defibrillator (AED), implantable cardioverter-defibrillator (ICD), or wearable cardioverter-defibrillator (WCD). We summarize the state of the art related to defibrillation in treating SCD, including a brief history of the evolution of defibrillation, technical characteristics of modern AEDs, strategies to improve AED access and increase survival, ancillary treatments, and use of ICDs or WCDs.

Treatment of out-of-hospital cardiac arrest (OHCA) requires prompt intervention. Better outcomes are associated with briefer time from dispatch of emergency medical services (EMS) providers to arrival on scene, application of a defibrillator or insertion of an advanced airway. We assessed whether time from receipt of a call by a telecommunicator to dispatch of EMS providers was associated with outcomes.

This was a retrospective analysis of a prospective cohort study of persons who had OHCA treated by EMS providers in Seattle, WA. Activation interval was defined as time from call pick up by telecommunicator to notification of EMS providers to respond to the call. Response interval was defined as the time from notification of EMS providers to their arrival at patient side. We determined the association between time intervals and outcomes of sustained restoration of spontaneous circulation (ROSC), survival to hospital discharge and neurologically favorable survival using multiple logistic regression. Secondary analyses assessed the relative contribution of activation versus response interval, and adjusted for post-treatment patient and EMS characteristics.

Among 2,687 patients, activation interval was mean 1.2 ± 0.6 min. Response interval was mean 6.1 ± 2.4 min. 1,232 (45.9%) achieved ROSC; 475 (17.7%) survived to discharge; and 428 (15.9%) had favorable neurologic status at discharge. Compared to an activation interval of at least 1.5 min, patients with briefer intervals were more likely to survive to discharge (adjusted odds ratio (OR) for <1 min, 1.69 (95% confidence interval (CI), 1.26, 2.28); adjusted odds ratio for 1 to 1.49 min, 1.54 (95% CI, 1.14, 2.08); p value = 0.002). With baseline survival of 10%, the absolute increase in survival associated with a 30 s decrease in activation interval was 0.7% and for a 30 s decrease in response interval was 0.4%.

Briefer activation interval was independently associated with greater survival. Further research is needed to assess whether reduction of the activation interval improves outcome after OHCA.

Survival after out-of-hospital cardiac arrest (OHCA) varies between communities, due in part to variation in the methods of measurement. The Utstein template was disseminated to standardize comparisons of risk factors, quality of care, and outcomes in patients with OHCA. We sought to assess whether OHCA registries are able to collate common data using the Utstein template. A subsequent study will assess whether the Utstein factors explain differences in survival between emergency medical services (EMS) systems.

Retrospective study.

This retrospective analysis of prospective cohorts included adults treated for OHCA, regardless of the etiology of arrest. Data describing the baseline characteristics of patients, and the process and outcome of their care were grouped by EMS system, de-identified, and then collated. Included were core Utstein variables and timed event data from each participating registry. This study was classified as exempt from human subjects’ research by a research ethics committee.

Thirteen registries with 265 first-responding EMS agencies in 13 countries contributed data describing 125,840 cases of OHCA. Variation in inclusion criteria, definition, coding, and process of care variables were observed. Contributing registries collected 61.9% of recommended core variables and 42.9% of timed event variables. Among core variables, the proportion of missingness was mean 1.9 ± 2.2%. The proportion of unknown was mean 4.8 ± 6.4%. Among time variables, missingness was mean 9.0 ± 6.3%.

International differences in measurement of care after OHCA persist. Greater consistency would facilitate improved resuscitation care and comparison within and between communities.

Quantitative measures of the ventricular fibrillation waveform at the outset of resuscitation are associated with survival. However, little is known about the course of these measures during resuscitation and how this course is related to outcome.

The purpose of this study was to determine how waveform measures change over the course of resuscitation and whether these changes might be used to guide resuscitation.

We evaluated 390 persons treated by emergency providers following out-of-hospital ventricular fibrillation arrest. We assessed the ventricular fibrillation waveform using the amplitude spectrum area (AMSA) from the defibrillator’s continuous electrocardiogram measured before each of the first three shocks. We used logistic regression to evaluate the relationship of AMSA and the change in AMSA with favorable neurologic survival as determined by the Cerebral Performance Category at hospital discharge 1-2.

Of the 390 patients who received an initial shock, 273 required a second shock and 210 required a third shock. The mean (standard deviation) for AMSA was 9.64 (0.52) for the 873 total shock cycles. AMSA₁ measured before the first shock was strongly associated with favorable neurologic survival (odds ratio [OR] 3.40, 95% confidence interval [CI] [2.48, 4.66] for 1 SD change). We observed a similar relationship for second-shock AMSA₂ (OR 3.53, 95% CI [2.42, 5.14]) and third-shock AMSA₃ (OR 3.10, 95% CI [2.03, 4.73]). The median change in AMSA was 0.24 for ΔAMSA_1-2 and 0.21 for ΔAMSA_2-3. A positive median change in AMSA between shocks was associated with favorable neurologic survival (OR 1.44, 95% CI [1.16, 1.80] for ΔAMSA_1-2 and OR 1.31, 95% CI [1.01, 1.71] for ΔAMSA_2-3).

Given their prognostic and dynamic qualities, quantitative waveform measures may provide an effective real-time strategy to guide individual treatment and improve survival.

Sudden cardiac arrest (SCA) due to ventricular arrhythmias is a major cause of mortality in western populations with up to 450,000 deaths in the United States each year. Although environmental factors clearly contribute to the determinants of SCA, familial aggregation studies and advances in the molecular genetics of inherited arrhythmias suggest that genetic factors confer susceptibility to SCA in the general population. Research in this area typically has focused on association of common genetic variants with intermediate phenotypes that predispose to SCA risk, such as QT interval, but few studies have examined genetic risk factors for SCA. We review the evidence for genetic susceptibility to SCA in the general population and focus on the studies published to date that have explored genetic risk factors.