The Value of Transesophageal Atrial Pacing in Predicting the Efficacy of Antiarrhythmic Drugs in Patients with Paroxysmal Narrow QRS Complex Tachycardia

Transesophageal atrial pacing (TAP) is used in the diagnosis and treatment of paroxysmal narrow QRS complex tachycardia (NQT). The aim of this study was to assess the value of this technique in predicting the efficacy of antiarrhythmic therapy. The study group consisted of 30 consecutive patients with spontaneous NQT whose clinical tachycardia was inducible by TAP. Baseline TAP was performed off all antiarrhythmic medication and repeated during oral antiarrhythmic drug therapy. The pacing protocol consisted of three stages: a single extrastimulus introduced at progressively shorter coupling intervals during sinus rhythm, pacing at incremental rates to the point of second-degree AV block, and bursts of rapid pacing. On repeat stimulation while on oral antiarrhythmic therapy (37 pacing studies) NQT was still inducible in 12 cases. During the follow-up period ten patients developed a recurrence of NQT:nine cases out of 12 (75%), in whom NQT was inducible while on antiarrhythmic therapy, and one case out of 25 (4%), in whom NQT was not inducible (P less than 0.001). The sensitivity of TAP in predicting the outcome of the patients with NQT was 90%, and the specificity 89%. The negative predictive value of TAP (prediction of no recurrence of NQT) was 96%, and the positive predictive value (prediction of recurrence of NQT) was 75%. We conclude that TAP is a simple and accurate method for predicting the efficacy of antiarrhythmic treatment in patients with NQT.     

Frequency Versus Time Domain Analysis of the Signal-Averaged Electrocardiogram: Reproducibility of the Spectral Turbulence Analysis

Reproducibility of the Spectral Turbulence Analysis. Spectral turbulence analysis (STA) of the signal-averaged electrocardiogram (ECG) is a new frequency domain method that analyzes the total high gain QRS complex and not only its terminal portion. This study examined the qualitative and quantitative short-term reproducibility of this technique (three recordings made within 25 min) in 68 subjects: 16 healthy volunteers; 22 patients with ventricular tachycardia and no evidence of heart disease; and 30 postinfarction patients with sustained ventricular tachycardia. The reproducibility of diagnosis of the STA was compared with that of the conventional time domain analysis of the signal-averaged ECG using standard criteria of abnormality. The reproducibility of numeric values of the spectral turbulence and of the time domain indices was performed by computing the ratios between standard deviation of measurements in individual subjects and standard deviations of all measurements. The reproducibility of diagnostic conclusions of the time domain analysis was slightly better than that of the STA but the differences were not significant (88%–91% of consistent time domain results vs 84% of consistent STA results). The numeric reproducibility of three STA parameters was slightly but not significantly inferior to that of the time domain indices whereas the reproducibility of the fourth STA variable, the intersegment correlation standard deviation (ISCSD), was significantly worse than that of the other indices. Of the two different ECG segments analyzed, the reproducibility of the STA variables calculated for the total QRS region was significantly better than that of the terminal low power QRS region. In conclusion, the qualitative and quantitative reproducibility of the STA is slightly but not significantly worse than that of the time domain analysis with the exception of the ISCSD, which is significantly less reproducible than all other parameters.     

Exercise producing alterations in the signal-averaged electrocardiogram in patients after myocardial infarction

Late potentials are considered to be a marker for regional slowconduction which might predispose to reentrant ventricular arrhythmias.Since these arrhythmias may be induced by ischaemia it may bespeculated that exercise-induced myocardial ischaemia may triggerlate potentials. Exercise testing was performed in 53 patients early after myocardialinfarction and in 20 healthy controls. Typical 12 lead ECG andsignal averaged ECG (SA-ECG) from 12 leads were recorded beforeand after exercise testing. Changes in filtered QRS (QRS) andlow amplitude signal durations, and in the root mean squarevoltage of the last 40 ms of the QRS complex (RMS40) were analysed.Tliirty patients developed ST changes, consistent with transientischaemia, that persisted during the SA-ECG recording afterexercise. There were significant differences between baselineSA-ECG and SA-ECG after exercise in patients with positive exercisetests (QRS, 102 ± 15 ms vs 114 ± 15 ms (P<0.01),LAS, 36 ± 12 ms vs 42 ± 11ms (P<0.05), andRMS40, 29± 14µV vs 20 ± 13µV (P<0.01)).No differences were observed in SA-ECG parameters in eitherpatients with negative exercise tests or in controls. During follow-up, four patients died suddenly; all four hadpositive exercise tests and in three of them late potentialswere induced by exercise. We conclude, that in post-infarction patients with positiveexercise tests SA-ECG parameters deteriorate after exercise.This suggests tltat exercise-induced ischaemia triggers developmentof late potentials.     

Relationship between signal-averaged electrocardiography and dangerous ventricular arrhythmias in patients with left ventricular aneurysm after myocardial infarction

We performed signal-averaged electrocardiography (SAECG) andHolter monitoring, and subsequently followed-up 53 ambulatorypatients with left ventricular aneurysm (LVA) after myocardialinfarction (MI). A history of spontaneous episodes of sustainedventricular tachycardia (VT) v also analysed. Out of 53 patients, 25 (47%) had an abnormal SAECG. AbnormalSAECG correctly identified nine out of 10 cases with a historyof sustained VT. Complex ventricular arrhythmias were detectedon Holler monitoring in 23 patients: in five out of 28 withnormal SAECG (18%) and in 18 out of 25 with abnormal SAECG (72%)(P<0001). During follow-up (mean 19 months) sustained VTand/or sudden cardiac death (SCD) occurred in eight cases, outof which seven had an abnormal SAECG. The negative predictivevalue of SAECG (no VT or SCD during follow-up) was very high,96%. similar to the negative predictive value of a history ofsustained VT (93%). Using multivariate analysis only a historyof sustained VT twas an independent factor in predicting theoutcome of patients in this study. We conclude that an abnormal SAECG identifies those post infarctionpatients with LVA who are prone to complex ventricular arrhvthmias.A normal SAECG and an absence of a history of sustained VT stronglyindicate that the risk of developing arrhythmic events is verylow.     

Influence of Filtering Techniques on the Time-Domain Analysis, Diagnosis, and Clinical Use of Signal-Averaged Electrocardiogram

In order to investigate the effect of different filtering techniques on the time-domain analysis of signal-averaged electrocardiogram (SAECG), recordings of 1,192 subjects were analyzed using Butterworth and Del Mar filters, both set at 40–250 Hz high and low pass frequencies. The recordings were taken from six clinically defined groups: (a) survivors of acute myocardial infarction (n = 553); (b) patients with sustained symptomatic postinfarction ventricular tachycardia (n = 89); (c) patients with hyperthropic cardiomyopathy (n = 219); (d) patients with dilated cardiomyopathy (n = 76); (e) direct relatives of patients with dilated cardiomyopathy (n = 170); and (f) normal healthy volunteers (n = 85). The study investigated differences between the SAECG results reported with both filters in three individual aspects: (l) numerical values of individual time-domain SAECG variables; (2) differences in SAECG findings of patients with postinfarction ventricular tachycardia and pair matched patients with uncomplicated follow-up after acute infarction; and (3) the power of SAECG findings to predict high risk of arrhythmic complication (sudden death and/or sustained ventricular tachycardia) among survivors of acute myocardial infarction. Compared with the Butterworth filter, the Del Mar filter led to a systematic difference of + 8% in total QRS duration, was equally powerful in distinguishing between the pair matched patients with and without postinfarction ventricular tachycardia, and was statistically significantly more powerful in identifying those survivors of acute infarction who were at high risk of arrhythmic complications. The study concludes that the use of different filters may produce discordant results of SAECG analysis. Normal and abnormal values for various types of SAEGG recording and analysis have to be established individually for different equipment and different software settings. These optimal cut-offs of SAEGG variables should also take into account the clinical characteristics of patient groups.     

Prediction of Antiarrhythmic Efficacy of Class I and III Agents in Patients with Ventricular Tachycardia by Signal-Averaged ECG Analysis

The effects of procainamide and dofetilide (pure Class III antiarrhythmic agent) on the signal-averaged ECG (SAECG) were examined in relation to the results of programmed ventricular stimulation studies in 25 patients with inducible sustained monomorphic ventricular tachycardia. Procainamide prolonged significantly the total QRS and low amplitude signal durations (140 ± 31 msec vs 166 ± 48 msec, P < 0.0001; 50 ± 25 msec vs 65 ± 38 msec, P < 0.002, respectively) whereas the root mean square voltage of the last 40 msec of the QRS complex was significantly reduced (22 ± 21 (iV vs 13 ± 12 p-V, P < 0,006). Procainamide was effective (prevention of the inducibility of sustained ventricular tachycardia or prolongation of the cycle length of ventricular tachycardia by > 100 msec) in 15 of 27 drug trials. Of the procainamide induced SAECG changes, the fractional prolongation of the total QRS duration was the best parameter that identified effectively treated patients (24%± 16% in responders vs 10%± 11% in nonresponders, P < 0.014). Afractional prolongation of the total QRS duration by > 15% identified effectively treated patients with a sensitivity of 87%, specificity of 81%, and an overall predictive accuracy of 84%. Dofetilide did not change the SAECG, and no SAECG parameter predicted the results of programmed ventricular stimulation. The effects of both drugs on the spectral analysis (area ratios) and on the spectral temporal mapping (the values of normality factor) of the SAECG were not consistent. In conclusion, antiarrhythmic efficacy of procainamide can be predicted by the degree of drug induced prolongation of the signal-averaged QRS complex. Dofetilide does not significantly affect the SAECG, and its efficacy cannot be predicted by the SAECG analysis.     

The value of time and frequency domain, and spectral temporal mapping analysis of the signal-averaged electrocardiogram in identification of patients with hypertrophic cardiomyopathy at increased risk of sudden death

Late potentials detected by the signal-averaged ECG (SAECG)identify post-infarction patients at risk from sustained ventriculartachycardia (VT) and sudden death. Hypertrophic cardiomyopathy(HCM) is also associated with increased risk of sudden death.In adults, episodes of non-sustained VT on ambulatory ECG monitoringare a marker of high risk patients. In children and adolescents,however, there is no reliable ECG marker, and clinical featureshave low predictive accuracy. The prognostic value of the SAECGin HCM has not been systematically evaluated. We examined the relation of detailed time domain, frequencydomain, and spectral temporal mapping analysis of the SAECGand clinical and echocardiographic features, and the resultsof 48 h ambulatory ECG monitoring in 121 consecutive patientswith HCM. Non-sustained VT on Holter monitoring was recordedin 27 (23%) patients. An abnormal time domain SAECG was presentin three (11%) patients with VT vs three (3%) without VT (ns).Of the SAECG variables, reduced (below 150 µ V) voltageof the initial 40 ms of the signal-averaged QRS complex wasthe best predictor for non- sustained VT (sensitivity: 95% specificity:74% ;positive predictive accuracy: 64%; negative predictiveaccuracy: 97%). Nine patients (of whom eight were 30 years ofage) experienced catastrophic events: three died suddenly andsix had been resuscitated from out-of-hospital ventricular fibrillation.None of them had an abnormal time domain SAECG. The frequencydomain analysis and spectral temporal mapping of the SAECG didnot improve the identification of patients with VT or patientswith catastrophic events. In conclusion, alterations of the initial portion of the signal-averagedQRS complex identified patients with HCM and non-sustained VT,but the SAECG was not useful in identifying young patients whosuffered cardiac arrest.