Abstract & Commentary
In this study, a European consortium of investigators evaluated the ability of an automatic external cardioverter defibrillator (AECD) to detect and treat arrhythmias in the in-hospital setting. The AECD used was the Powerheart model manufactured by Cardiac Science Inc, in Irving, Calif. The device uses self-adhesive electrodes placed on the thorax. The AECD continuously monitors, analyzes, and classifies the ECG rhythm of attached patients. Te thorax. The AECD continuously monitors, analyzes, and classifies the ECG rhythm of attached patients. The device can function in either an automatic mode in which it treats arrhythmias without operator intervention or in an advisory mode in which an operator is required to press a button to deliver a shock. The device is not committed to shock since it reanalyzes the rhythm again after charging. The device is currently approved by the Food and Drug Administration for in-hospital use. In this study, 117 patients were monitored. Fifty-one of the patients were in intensive care or telemetry units, and 66 patients were monitored during either electrophysiologic studies or implantable cardioverter defibrillator (ICD) implantations. Eleven of the patients were in persistent atrial fibrillation.
Data from a total of 125 hours of monitoring during invasive procedures and 1115 hours of monitoring in the ward settings were analyzed. During invasive procedures, there were a total of 34, 5, and 16 episodes of monomorphic and polymorphic VT and VF, respectively. On the monitored wards, there were 10 episodes of monomorphic VT, 2 episodes of polymorphic VT, and 17 episodes of VF documented. During monitoring, there were 1454 true-negatives, 499 true-positives, 35 false-positives, and no false-negatives. This resulted in a sensitivity of 100% and a specificity of 97.6%. Most of the false-positives resulted from T-wave oversensing during ventricular pacing. In standard clinical use, ventricular pacing is a contraindication to use of the AECD, but patients with pacemakers could be included in this trial if their devices were only in the advisory mode. Inappropriate therapy was never delivered. Movement artifact caused initial arrhythmia detections in 3 patients on 5 occasions, but reanalysis quickly classified this as artifact within 2-4 seconds. Thirty-five episodes were treated with shock therapy. All converted to normal rhythms with a response time of 14 ± 4 seconds.
Martinez-Rubio and colleagues concluded that early automatic defibrillation of patients who suffer an in-hospital cardiac arrest is now feasible with an external device that is fast, safe, and effective for detecting and classifying arrhythmias (Martinez-Rubio A, et al. J Am Coll Cardiol. 2003;41:627-632).
Comment by John DiMarco, MD, PhD
In-hospital cardiac arrest is still associated with a significant mortality. On unmonitored wards, survival rates are quite low, particularly if the arrest occurs during nocturnal hours. Even in monitored settings, response times are usually measured in minutes rather than in seconds, and this delay may have an adverse effect on survival.
The AECD discussed here provides a temporary alternative to an implantable device in high-risk patients. However, it remains to be seen how these devices may be integrated into patient care. In the intensive care unit setting, the improvement in time to shock delivery is relatively small, and I doubt that the cost involved in AECD use can be justified. In the ward setting, the event rates are quite low, and it would be difficult to devise a strategy that would justify widespread use of these devices on unmonitored wards. Even on telemetry wards, the event rates are quite low, and devising a cost-effective strategy for their use would be difficult. It should also be recognized that there is a wearable automatic external defibrillator made by Life-Cor, in Pittsburgh, Penn. This device is worn externally as a vest and actually can be used either in or outside the hospital.
I anticipate that the major use of an AECD might be during the transport of patients who have significant risk for life-threatening ventricular arrhythmias. These patients are usually transported on a monitor, with a skilled nurse. Use of the AECD might allow them to be transported through