Several methods for enhancing the functioning of defibrillators in cases of heart attack

Mar 26 2008

The PhD, defended by engineer Sofia Ruiz de Gauna Gutierrez at the University of the Basque Country (UPV/EHU) puts forward various methods for the elimination of interference caused by compressions and ventilations of cardiopulmonary resuscitation in the context of cardiac defibrillation.

A heart attack, also known as myocardial infarction or coronary thrombosis, is the most dramatic manifestation of cardiovascular illness, the main cause of death in developed countries.

In more than 40% of heart attacks patients can have two types of cardiac arrhythmias: ventricular or tachycardial ventricular fibrillation without pulse. The optimum treatment in these cases is the immediate initiation of cardiopulmonary resuscitation (CPR) to maintain artificial circulation by means of the application of thoracic compressions and ventilations, followed by an electrical discharge on the patient's chest (defibrillation) when the cardiac rhythm is defibrillable. There is evidence that the success of the defibrillation is directly related to the immediacy with which the discharge is administered.

The automatic external defibrillator (AED) is a device capable of analysing the electrocardiogram and applying, if necessary, defibrillation. The mechanical activity of the thoracic compressions and ventilations induces interference on the electrocardiogram that compromises the reliability of the AED diagnosis. Consequently, cardiopulmonary resuscitation has to be interrupted during the intervals of automatic analysis, causing the absence of circulation and reducing the probability of success of electrical therapy.

This was the theme of the PhD thesis by Ms Sofía Ruiz de Gauna Gutiérrez at the higher technical School of Engineering of the UPV/EHU, a work in which various methods for the elimination of this interference caused by compressions and ventilations of the cardiopulmonary resuscitation itself were proposed. The interference-free electrocardiograph signal enables the defibrillator to correctly diagnose during the CPR procedure, avoiding the interruption of compressions and enabling the administration of the discharge as soon as possible.

The PhD, entitled Eliminación de la interferencia debida a la resucitación cardiopulmonar en el contexto de la desfibrilación cardíaca (Elimination of interference due to cardiopulmonary resuscitation in the context of cardiac defibrillation) was led by the Head of the Department of Electronics and Telecommunications, Ms Elisabete Aramendi Ecenarro, and obtained summa cum laude. The PhD was carried out with help from the Osatu S. Coop. company, the Hospital of Cruces, the Hospital Donostia and the University of Stavanger (Norway).

Ms Sofía Ruiz de Gauna Gutiérrez is a Telecommunications Engineer from the University of the Basque Country and currently collaborating lecturer with the UPV/EHU.

Elimination of interference

In this work various methods for the elimination of interference caused by compressions and ventilations of the cardiopulmonary resuscitation are put forward. The methods of filtration designed are divided into two groups: those that only analyse the information of the electrocardiogram registered by the AED and those that require additionally a single signal of reference to estimate the interference.

The methods have been evaluated using signals obtained from real resuscitation events undertaken by emergency service crews in various locations. The results for sensitivity and specificity obtained are similar to those of other published methods of greater complexity, and so support the hypothesis that analysis of cardiac rhythm is possible during cardiopulmonary resuscitation. Nevertheless, the elimination of interference in non-defibrillable rhythms presents greater difficulty and has to be investigated further in this regard.

The methods designed can be easily incorporated into current AEDs, with minimum modifications to their configuration. The AED diagnosis would be sufficiently reliable for the recommendation of a discharge during the cardiopulmonary resuscitation procedure, and thus the defibrillation decision can be facilitated. This fact supports the current tendency to administer compressions continuously, without unnecessary interruptions and augmenting, in the last analysis, the probability of defibrillation success.