Effects of mexiletine, propafenone and flecainide on signal-averaged electrocardiogram

Abnormal signal-averaged electrocardiograms in patients with incomplete right bundle-branch block

BACKGROUND AND HYPOTHESIS

A hypothesis was formulated that regional delayed activation of the right ventricle, as seen in incomplete right bundle-branch (IRBBB) aberrancy, may simulate late potential activity and may be responsible for abnormal signal-averaged electrocardiograms (SAECGs). No previous studies have specifically addressed this issue in this particular group of patients (with IRBBB). Therefore, the aim of the present study was to investigate the incidence of abnormal SAECGs in patients with IRBBB. If this were confirmed, our purpose would further be to investigate ways of reducing the false positive results.

METHODS

The study group included 53 patients (28 men and 25 women), aged 53 +/- 13 years, with no history of previous myocardial infarction or ventricular tachycardia and who had an electrocardiogram (ECG) showing IRBBB. An SAECG was also performed in a control group of 19 age-matched individuals with a normal ECG. Time domain analysis was performed using a band pass filter of 40-250 Hz. The following parameters were considered normal: filtered QRS duration (QRSD) < 114 ms, root mean square of the voltage of the last 40 ms of the QRS complex (RMS) > 20 microV, and the duration of the low amplitude signal (< 40 microV) at the terminal portion of the QRS (LAS) < 38 ms. An SAECG was considered abnormal if any two of these criteria were abnormal.

RESULTS

The mean values of the SAECG parameters were: QRSD 101 +/- 11 ms, RMS 32 +/- 20 microV, LAS 32 +/- 12 ms, and noise 0.29 +/- 0.13 microV. Abnormal SAECGs with at least two criteria satisfied were present in 16 of 53 (30%) patients compared with 0 (0%) of 19 individuals in the control group (p = 0.02). Abnormal values included the combination of RMS and LAS in 12 patients and all three parameters in 4 patients. However, if the definition of late potentials were limited to the combination of abnormal QRSD and either RMS or LAS values, the incidence of false positive results (4 patients) (7.5%) would be significantly decreased (p = 0.007). At 21 months of follow-up, no arrhythmic events occurred.

CONCLUSIONS

Delayed terminal conduction observed in IRBBB may cause a high incidence of false positive late potentials on SAECGs. Based on this study, we propose that this can be largely remedied if the optimal criteria for the presence of late potentials in patients with IRBBB always include the combination of QRSD and either RMS or LAS.

Pharmacodynamic equivalence of two flecainide acetate formulations in patients with paroxysmal atrial fibrillation by QRS analysis of ambulatory electrocardiogram

The pharmacodynamic equivalence of flecainide acetate immediate-release (IR) and controlled-release (CR) formulations was assessed from QRS duration in patients currently treated with the IR formulation. Patients were blindly assigned randomly to the IR (100 mg BID, n = 25) or to the CR group (200 mg OD, n = 23). Electrocardiographic parameters were measured at baseline and at week 8 from 24-h Holter monitoring. Mean (SD) normalized flecainide trough plasma concentration (measured 12 h after last intake) at week 8 was 381.3 ng/ml (104.8) with the IR and 381.4 ng/ml (123.8) with the CR formulation. Hodges-Lehmann estimate (95% CI) of the difference between IR and CR for change in QRS duration between baseline and week 8 was 1.6% (-0.1; 3.7), indicating that the formulations were pharmacodynamically equivalent. Median QRS values (102 vs 100.1 ms at baseline; 103.15 vs 99 ms at week 8) as well as first and third quartiles were very similar in both groups. The correlation between QRS duration and RR classes at baseline was highly significant (P < 0.0001). Correlation coefficient at week 8 was statistically significant for > 50% of the patients and was significant in a greater proportion of patients under the IR compared with the CR formulation. Circadian hourly variations of QRS duration as determined by harmonic analysis showed the occurrence of a peak of QRS widening following each intake of the IR, whereas this pattern was not observed with the CR formulation. The latter results are consistent with a greater occurrence of frequency-dependent QRS variations over the 24-h period with the IR compared with the CR formulation.

Absence of change of signal-averaged electrocardiogram identifies patients with ventricular arrhythmias who are non-responders to amiodarone

OBJECTIVES

The aim of this study was to assess the ability of a non-invasive study, the signal-averaged ECG (SAECG), to predict the effect of amiodarone at ventricular level.

BACKGROUND

Amiodarone is the main drug drug used in the treatment of ventricular arrhythmias. Standard ECG does not detect any change in QRS complex resulting from amiodarone therapy. SAECG is more sensitive than ECG for detecting changes in QRS complex.

METHODS

The study examined the effects of amiodarone on SAECG in relation to the results of programmed ventricular stimulation in 68 patients with old myocardial infarction, spontaneous and inducible sustained ventricular tachycardia (VT).

RESULTS

Amiodarone prolonged the total QRS duration (dur) (129+/-28 vs. 140+/-30 ms, P<0.05) and low amplitude signal (LAS) dur (45+/-20 vs. 51+/-20 ms, P<0.1), whereas the root-mean-square voltage of the last 40 ms of QRS complex (RMS 40) was significantly reduced (20+/-16 vs. 14+/-9 microV, P<0.05). Changes in SAECG parameters did not differ significantly in patients in whom amiodarone prevented the inducibility of VT (n=15) and those in whom VT remained inducible with amiodarone (n=53), but in baseline QRS duration was significantly shorter in patients in whom amiodarone prevented the VT induction (118+/-26 vs. 133+/-28 ms, P<0.05). In patients in whom amiodarone did not prolong the cycle length of VT (n=15), SAECG did not change significantly (QRS dur 131+/-29 vs. 132+/-27 ms, LAS 42+/-20 vs. 42+/-19 ms, RMS 40 22+/-14 vs. 19+/-11 microV). Comparison of the SAECG data in patients with no inducible VT and those with slowed VT differed significantly (P<0.05) between the control state and the recording with amiodarone.

CONCLUSIONS

The effects of amiodarone on VT inducibility are predicted by a shorter baseline QRS duration and the degree of drug-induced prolongation of filtered QRS duration. Amiodarone prolonged the QRS duration, LAS duration and decreased RMS 40; this effect was more important in patients with no inducible VT and in those with only slowed VT, than in patients with unchanged or accelerated VT. The absence of changes of QRS duration predicted the induction of a more rapid or not slowed VT with amiodarone with a sensitivity of 87% and a specificity of 83%. Therefore, SAECG appears as an useful and simple means to predict the effects of amiodarone in patients with myocardial infarction and VT.

The effects of intravenous mexiletine on spectra of the signal-averaged ECG

This study examined the effects of intravenous mexiletine on the time-domain and spectrotemporal signal-averaged ECG (SAECG). SAECGs were recorded in 60 postmyocardial infarction (MI) patients with more than 100 premature ventricular beats per hour, before and after a constant infusion of mexiletine, 7 mg/kg, given over 1 hour. Spectrotemporal analysis was done on a fixed analyzed signal duration of QRS complex and ST segment of X, Y, and Z leads using a temporal window of rectangular type, measuring the signal content between 10-120 Hz. Intravenous mexiletine produced no significant change in the mean values of any of the time-domain variables. However, mexiletine either increased or decreased the power density spectrum (PDS) and PDS ratio (40-120 Hz/25-120 Hz) of the SAECG, and in rare cases only did it not alter the spectra of the SAECG. When PDS ratio in lead Z decreased after mexiletine, it was usually higher at baseline in comparison with that when the PDS ratio increased, or vice versa. When the treatment with mexiletine was effective, PDS increased in comparison with that when the drug was ineffective, or vice versa. Not all ranges (10-120 Hz) of spectra of the SAECG, but only certain frequency bands (25-40 Hz in lead Z, P = 0.0253; 40-55 Hz in lead Y, P = 0.0096; 55-70 Hz in X lead, P = 0.0018; and in lead Z, P = 0.0002; 70-85 Hz in lead X, P = 0.0025; and in lead Z, P = 0.0075, 85-100 Hz in lead X, P = 0.0033) were associated with mexiletine efficacy.(ABSTRACT TRUNCATED AT 250 WORDS)

Signal-averaged ECG in prediction of the short-term suppression of ventricular premature beats by Mexiletine

We analyzed whether baseline parameters of time-domain and spectrotemporal analysis of a signal-averaged ECG or their changes during Mexiletine therapy can predict the antiarrhythmic efficacy of the drug. On 60 post-MI patients with > 100 ventricular premature beats per hour, signal-averaged ECGs were recorded before and after a constant infusion of Mexiletine (7 mg/kg) for 1 h and again after 4 days of oral Mexiletine therapy (Mexiletine SR, 360 mg twice daily). Spectrotemporal analysis was performed on a fixed analyzed signal duration of QRS-complex and ST-segment of X-, Y-, Z-leads using the temporal window of the rectangular type, measuring signals between 10-20 Hz. Intravenous and oral Mexiletine did not produce significant changes in mean values of any time-domain parameters. However, using informative variables of spectra of the signal-averaged ECG, we managed retrospectively to predict antiarrhythmic efficacy in 92% of the patients. Only certain frequency bands (from the range of the spectra at baseline, 10-120 Hz) were predictive for intravenous Mexiletine efficacy: 40-55 Hz in lead Y (P = 0.0116); 55-70 Hz in leads X and Z (P = 0.0063 and P = 0.0269, respectively); 70-85 Hz in lead Z, (P = 0.0227). When the treatment with intravenous Mexiletine was effective, the baseline power spectrum density was lower than when the drug was ineffective, and vice versa. Moreover, the efficacy of oral Mexiletine can be predicted by power density spectrum at baseline (10-25 Hz in lead Z, P = 0.0210; 70-85 Hz in lead Y, P = 0.0254) and by one of the possible (increased, decreased, unchanged) effects of intravenous Mexiletine on the spectra at frequency bands (70-85 Hz in lead X, P = 0.0432 and 40-120 Hz in lead Z, P = 0.0156). These results show the value of spectrotemporal signal-averaged ECG in selecting a subgroup of post-myocardial infarction patients that may benefit from Mexiletine therapy.

Effects of procainamide on the signal-averaged electrocardiogram in relation to the results of programmed ventricular stimulation in patients with sustained monomorphic ventricular tachycardia

OBJECTIVES

The aim of this study was to assess the ability of the signal-averaged electrocardiogram (ECG) to predict the efficacy of procainamide.

BACKGROUND

The main role of the signal-averaged ECG has been the identification of postinfarction patients at risk of sudden death. Prediction of the efficacy of antiarrhythmic drugs represents another potential clinical application of this technique.

METHODS

The study examined the effects of procainamide on the time domain and spectral temporal analysis of the signal-averaged ECG in relation to the results of programmed ventricular stimulation studies in 31 patients with inducible sustained monomorphic ventricular tachycardia.

RESULTS

Procainamide significantly prolonged the total and the initial QRS complex and low amplitude signal durations (mean +/- SD 135 +/- 30 vs. 161 +/- 46 ms, p < 0.0001; 87 +/- 16 vs. 98 +/- 20 ms, p < 0.0001, and 48 +/- 23 vs. 63 +/- 36 ms, p < 0.001, respectively) whereas the root-mean-square voltage of the total QRS complex and of the last 40 ms of the QRS complex was significantly reduced (mean +/- SD 112 +/- 36 vs. 87 +/- 36 microV, p < 0.0001; 21 +/- 19 vs. 13 +/- 12 microV, p < 0.002, respectively). The results of spectral temporal mapping of the signal-averaged ECG were similar before and after procainamide administration. Procainamide prevented the inducibility of sustained ventricular tachycardia or prolonged the cycle length of ventricular tachycardia by > or = 100 ms in 16 patients (52%) (responders). The fractional prolongation of the total QRS duration was significantly greater in responders (26 +/- 15%) than in nonresponders (10 +/- 10%) (p < 0.002) and, when this prolongation was > or = 15%, identified responders with a sensitivity of 94%, a specificity of 87% and an overall predictive accuracy of 90%.

CONCLUSIONS

The effects of procainamide on inducibility of ventricular tachycardia during programmed ventricular stimulation can be predicted by the degree of drug-induced prolongation of the signal-averaged QRS complex.