ARRHYTHMIAS AND CONDUCTtON DtSTURBANCES
Signal-Averaged Electrocardiographic Late Potentials in Resuscitated Survivors of Out-of-Hospital Ventricular Fibrillation G. Lee Dolack, MD, David B. Callahan, Gust H. Bardy, MD, and H. Leon Greene, MD The results of signal-averaged ekctrocardiography and programmed electrical stimubtion were evaluated In 25 patients wRh recurrent sustained ventricular tachycardii (VT) and 46 patients with a history of out-of-hospRal ventrkular fibrillation (VF) to characterize the ekctrophysiologk substrate responsible for these different cfinkal arrhythmia presentations. Patients with VT had a higher incidence of late potentials (VT 63%, VF so%, p = O&OS). SignRkant differeMes between these groups were ako noted in response to programmed ekctrkal stimulation. A sustained ventricular arrhythmia was induced in 24 of 25 (96%) patientrwithaM~oryofVTbutinonly27of46 (59%) of VF patients (p = 0.00s). In additfon, VF was induced in 11(24%) patients in the VF group butinnoneotthepeUenhintheVTgroup(p= 0.00s). When the 2 groups were compared on the basis of sekct clinical characteristks, no significant difference in age, sex, presence of coronary artery disease or ejection fraction was noted. The frequency of prior myocardial infarction was significantly higher in the VT group (VT 20 of 25, So%; VF 24 of 46,52%; p = 0.03). Finally, no significant relation between the presence of late potentials and htduced arrhythmias was noted in either group. The inability of signal-averaged efectrocardiography to predkt inducibifii in VF patients may represent a sigtdfkant limitation of this technique in identjfyhrg patients at risk for sudden cardiac death. (Am J Cardid 1990;6J:l102-1104)
ignal-averagedelectrocardiographyhasbeenextensively evaluatedin survivors of myocardial infarction and in patients with both sustainedand nonsustainedventricular tachycardia (VT).1-12Late potentials detected by this technique are high frequency, low amplitude signals in the terminal portion of the QRS recorded during sinus rhythm. These signals are thought to correlate with similar potentials recorded in the border zone of experimental myocardial infarction and in animal models of VT.13-14Mapping studies suggest that late potentials represent slowed conduction through diseasedmyocardium, i.e., the substrate for reentry.13-15Recent reports suggest that the presenceof late potentials correlates with subsequent arrhythmic events and inducibility during programmed electrical stimulation.4-6J6-*8Survivors of out-of-hospital cardiac arrest representa group with a high likelihood of recurrent clinical ventricular arrhythmias.lg We and others have suggestedthat the electrophysiologic substrate in patients who present with ventricular fibrillation (VF) might be different from that in patients with clinical VT.6J6*20*21 This study compares the frequency of late potentials in patients with VF to patients with VT and evaluatestheir relation to clinical variables and results of programmed electrical stimulation.
S
METHODS Patien& Seventy-oneconsecutivesubjectswere pro-
spectively evaluated by signal-averagedelectrocardiography: 25 had a history of recurrent sustained VT, and 46 patients were evaluated after an episode of out-ofhospital cardiac arrest secondary to documented VF. All subjects were evaluated in the drug-free state at least 5 half-lives after the last antiarrhythmic drug dose, as documented by serum drug levels. No patient had ever taken amiodarone. All patients with atria1 librillation, bundle branch block or nonspecificintraventricular conduction disturbance were excluded from the study. Ssgnal-averaged ekctrocardiography: Signal-averaged electrocardiography was performed with an IBM PC-AT-based ensemble(Corazonix Corp.). Recordings were processedand analyzed based on methods described by Simson et al1 and Denes et a1.20The device From the Division of Cardiology, Harborview Medical Center and the recorded signals at the patient’s bedside during sinus University of Washington Medical Center, Seattle, Washington. This rhythm in a standard, bipolar, orthogonal XYZ lead study wassupportedin part by grants HL36170 and HL3 1472from the National Institutes of Health, Bethesda,Maryland, and grants from the format. Averaging was continued until the noise level American Heart Association, Washington Affiliate, the Emergency late in the ST segmentwas 120 ms. Signals were analyzed without knowledge of the clinical status of the patient. Electrophysidogic testing: After signal-averaged electrocardiography, all patients underwent electrophysiologic study with a standardized protocol. All studies were performed after discontinuation of antiarrhythmic therapy for at least 5 drug half-lives. Ventricular stimulation utilized a 1 ms squarewave pulse at twice diastolic threshold. The pacing protocol included single, double and triple extrastimuli delivered after 2 basic drive cycle lengths (600 and 400 ms) at 2 right ventricular sites. The endpoint of the study was completion of the protocol or induction of a sustained ventricular arrhythmia. A sustained ventricular arrhythmia was defined as VT or VF lasting >30 secondsor requiring overdrive pacing or cardioversion becauseof hemodynamic compromise. VF was defined as sustained ventricular arrhythmia with a cycle length 1240 ms with variable QRS morphology in leads I, II, III and VI. Nonsustained VT was defined as reproducible induction of 16 beats and
Signal-Averaged Electrocardiographic Late Potentials in Resuscitated Survivors of Out-of-Hospital Ventricular Fibrillation G. Lee Dolack, MD, David B. Callahan, Gust H. Bardy, MD, and H. Leon Greene, MD The results of signal-averaged ekctrocardiography and programmed electrical stimubtion were evaluated In 25 patients wRh recurrent sustained ventricular tachycardii (VT) and 46 patients with a history of out-of-hospRal ventrkular fibrillation (VF) to characterize the ekctrophysiologk substrate responsible for these different cfinkal arrhythmia presentations. Patients with VT had a higher incidence of late potentials (VT 63%, VF so%, p = O&OS). SignRkant differeMes between these groups were ako noted in response to programmed ekctrkal stimulation. A sustained ventricular arrhythmia was induced in 24 of 25 (96%) patientrwithaM~oryofVTbutinonly27of46 (59%) of VF patients (p = 0.00s). In additfon, VF was induced in 11(24%) patients in the VF group butinnoneotthepeUenhintheVTgroup(p= 0.00s). When the 2 groups were compared on the basis of sekct clinical characteristks, no significant difference in age, sex, presence of coronary artery disease or ejection fraction was noted. The frequency of prior myocardial infarction was significantly higher in the VT group (VT 20 of 25, So%; VF 24 of 46,52%; p = 0.03). Finally, no significant relation between the presence of late potentials and htduced arrhythmias was noted in either group. The inability of signal-averaged efectrocardiography to predkt inducibifii in VF patients may represent a sigtdfkant limitation of this technique in identjfyhrg patients at risk for sudden cardiac death. (Am J Cardid 1990;6J:l102-1104)
ignal-averagedelectrocardiographyhasbeenextensively evaluatedin survivors of myocardial infarction and in patients with both sustainedand nonsustainedventricular tachycardia (VT).1-12Late potentials detected by this technique are high frequency, low amplitude signals in the terminal portion of the QRS recorded during sinus rhythm. These signals are thought to correlate with similar potentials recorded in the border zone of experimental myocardial infarction and in animal models of VT.13-14Mapping studies suggest that late potentials represent slowed conduction through diseasedmyocardium, i.e., the substrate for reentry.13-15Recent reports suggest that the presenceof late potentials correlates with subsequent arrhythmic events and inducibility during programmed electrical stimulation.4-6J6-*8Survivors of out-of-hospital cardiac arrest representa group with a high likelihood of recurrent clinical ventricular arrhythmias.lg We and others have suggestedthat the electrophysiologic substrate in patients who present with ventricular fibrillation (VF) might be different from that in patients with clinical VT.6J6*20*21 This study compares the frequency of late potentials in patients with VF to patients with VT and evaluatestheir relation to clinical variables and results of programmed electrical stimulation.
S
METHODS Patien& Seventy-oneconsecutivesubjectswere pro-
spectively evaluated by signal-averagedelectrocardiography: 25 had a history of recurrent sustained VT, and 46 patients were evaluated after an episode of out-ofhospital cardiac arrest secondary to documented VF. All subjects were evaluated in the drug-free state at least 5 half-lives after the last antiarrhythmic drug dose, as documented by serum drug levels. No patient had ever taken amiodarone. All patients with atria1 librillation, bundle branch block or nonspecificintraventricular conduction disturbance were excluded from the study. Ssgnal-averaged ekctrocardiography: Signal-averaged electrocardiography was performed with an IBM PC-AT-based ensemble(Corazonix Corp.). Recordings were processedand analyzed based on methods described by Simson et al1 and Denes et a1.20The device From the Division of Cardiology, Harborview Medical Center and the recorded signals at the patient’s bedside during sinus University of Washington Medical Center, Seattle, Washington. This rhythm in a standard, bipolar, orthogonal XYZ lead study wassupportedin part by grants HL36170 and HL3 1472from the National Institutes of Health, Bethesda,Maryland, and grants from the format. Averaging was continued until the noise level American Heart Association, Washington Affiliate, the Emergency late in the ST segmentwas 120 ms. Signals were analyzed without knowledge of the clinical status of the patient. Electrophysidogic testing: After signal-averaged electrocardiography, all patients underwent electrophysiologic study with a standardized protocol. All studies were performed after discontinuation of antiarrhythmic therapy for at least 5 drug half-lives. Ventricular stimulation utilized a 1 ms squarewave pulse at twice diastolic threshold. The pacing protocol included single, double and triple extrastimuli delivered after 2 basic drive cycle lengths (600 and 400 ms) at 2 right ventricular sites. The endpoint of the study was completion of the protocol or induction of a sustained ventricular arrhythmia. A sustained ventricular arrhythmia was defined as VT or VF lasting >30 secondsor requiring overdrive pacing or cardioversion becauseof hemodynamic compromise. VF was defined as sustained ventricular arrhythmia with a cycle length 1240 ms with variable QRS morphology in leads I, II, III and VI. Nonsustained VT was defined as reproducible induction of 16 beats and
