Signal-averaged P-wave Research Articles

History Repeats Itself

To the Editor: In a recent issue of Circulation , Zaman et al1 report a model for the preoperative risk stratification of patients at risk for developing atrial fibrillation (AF) after isolated coronary artery bypass grafting (CABG). They studied 326 patients prospectively and demonstrated that prolonged signal-averaged P-wave duration (SAPD), advanced age, and male sex identified patients at a high risk for post-CABG AF. Moreover, there was an incremental increase in risk for patients with >1 of these 3 variables. We agree with the authors that a predictive model for patients at risk for post-CABG AF could be useful for the management of this common complication. Advanced age was identified as an important predictor, and this has been consistently reported as a risk factor in prior studies.2 3 Male sex was identified as a risk in one prior report but not in the majority of other existing studies.4 The authors also highlight the …

Signal-averaged P-wave duration does not predict atrial fibrillation after thoracic surgery.

Atrial fibrillation (AF) is the most common dysrhythmia seen early after major thoracic surgery but occurs infrequently after minor thoracic or other operations. A prolonged signal-averaged P-wave duration (SAPWD) has been shown to be an independent predictor of AF after cardiac surgery. The authors sought to determine whether a prolonged SAPWD alone or in combination with clinical or echocardiographic correlates predicts AF after elective noncardiac thoracic surgery. Of the 250 patients enrolled, 228 were included in the final analysis. Preoperative SAPWD was obtained in 155 patients who had major thoracic surgery and in 73 patients undergoing minor thoracic or other operations who served as comparison control subjects. The SAPWD was recorded from three orthogonal leads using a sinus P-wave template. The filtered vector composite was used to measure total P-wave duration. Clinical, surgical, and echocardiographic parameters were collected and patients followed for 30 days after surgery for the development of symptomatic AF. Symptomatic AF developed in 18 of 155 (12%) patients undergoing major thoracic surgery and in 1 of 73 (1%) patients having minor thoracic or abdominal surgery, most commonly 2 or 3 days after surgery. In comparison with similar patients undergoing major thoracic surgery without AF, those who developed AF were older (66+/-8 vs. 62+/-10 yr; P = 0.04) but did not differ in SAPWD (145+/-17 vs. 147+/-16, ms) in standard electrocardiographic P-wave duration (105+/-7 vs. 107+/-10 mns), incidence of left-ventricular hypertrophy on 12-lead electrocardiography, male sex, history of hypertension, diabetes, or coronary heart disease. Thoracic-surgery patients at risk for postoperative AF did not differ from all other patients at low risk for AF in clinical or SAPWD parameters. Under the conditions of this study, SAPWD did not differentiate patients who did or did not develop AF after noncardiac thoracic surgery, and therefore its measurement cannot be recommended for the routine evaluation of these patients. Older age continues to be a risk factor for AF after thoracic surgery.

Acute effects of caffeine ingestion on signal-averaged electrocardiograms

Background Although moderate caffeine ingestion has not been shown to be arrhythmogenic, caffeine toxicity can cause severe cardiac arrhythmias, including atrial fibrillation and ventricular tachycardia. Atrial fibrillation and ventricular tachycardia have been associated with prolongation of P-wave and QRS complex durations on signal-averaged electrocardiograms. This study investigated acute effects of caffeine ingestion on signal-averaged P-wave and QRS complexes. Methods and Results Signal-averaged electrocardiograms were obtained from 12 normal subjects (6 men, 6 women; ages 21 to 26 years) before and after ingestion of caffeine (5 mg/kg body weight) or placebo in a randomized, double-blind, crossover fashion. Electrocardiograms for signal averaging were recorded from electrodes left in a constant location. After bandpass filtering (30 to 300 Hz) and amplification, signals were sampled over 7.2 minutes at 2000 Hz. Signal-averaged P-wave and QRS complex durations did not significantly change after placebo ingestion. After caffeine ingestion QRS duration prolonged in 9 of 11 subjects at 90 minutes (mean ± SEM = 0.8 ± 0.3 ms, P < .02) and in 8 of 9 after 3 hours (1.1 ± 0.2 ms, P < .001). No significant change in P-wave duration or heart rate was found after caffeine ingestion at any test interval. Average caffeine level in saliva 90 minutes after ingestion was 6.6 ± 1.6 (SD) μg/dL. Conclusions Although probably not arrhythmogenic in normal subjects, moderate caffeine ingestion does produce a small but statistically significant prolongation of signal-averaged QRS complexes. Further prolongation caused by excessive caffeine intake may be a factor in the genesis of arrhythmias associated with caffeine toxicity. (Am Heart J 1998;136:643-6.)

The signal averaged P wave in atrioventricular block—evidence for abnormal atrial conduction?

The incidence of atrial fibrillation in patients with atrioventricular block (AVB) appears increased over that for the unpaced population even if atrioventricular synchrony is maintained by dual chamber pacing. To assess whether atrial fibrillation in these patients might be due to concurrent abnormality in atrial activation we performed signal averaged P wave (SAPW) recordings in 15 patients with dual chamber pacemakers implanted for AVB and compared the results to those from 21 unpaced controls. The median (range) age was 69 (53–89) years for patients and 60 (51–78) years for controls. Eleven patients and 12 controls were male. All patients were pacing in VDD mode at the time of study. SAPW recordings were obtained using our previously reported selective P wave averaging system. We measured P wave duration after high pass filtering at 40 Hz, the rate of change of P wave voltage over time (spatial velocity) and low and high frequency spectral energy after Fourier transformation of the P wave signal. We found increased P wave duration, mean spatial velocity and lower frequency energy in patients with AVB compared to controls [duration, 144 (5) vs. 134 (2) ms, p<0.05; mean spatial velocity, 5.6 (0.4) vs. 4.6 (0.1) mV/s, p<0.05; energy 20–150 Hz, 57.4 (8.2) vs. 36.3 (2.8) μV 2·s, p<0.01. All values mean (SEM)]. These results suggest that the increased incidence of atrial fibrillation in patients paced for AVB may be related to intrinsic abnormalities of atrial activation and not solely to the pacing mode. Ensuring sequential atrioventricular pacing in these patients may not completely abolish the increased incidence of atrial fibrillation.

Correlation between initial potentials on a signal-averaged P-wave and indice of electrophysiologic measurements in the right atrium.

The aim of this study was to determine whether initial potentials of the P-wave on a signal-averaged electrocardiogram (SAE) during sinus rhythm reflect indices of electrophysiologic measurements in the high lateral right atrium. A total of 67 patients underwent P-wave signal averaging during electrophysiologic testing. The correlation between root mean square voltages for the initial 10 and 20 msec of the P-wave on the SAE and indices of electrophysiologic measurements, sinus node recovery time (SRT) and sinoatrial conduction time (SACT), obtained from programmed stimuli, was evaluated. It was found that the initial potentials of the P-wave on the SAE correlated negatively with SRT and SACT (-0.37 < or = r < or = -0.30). It was concluded that the initial potentials correlated with indices of electrophysiologic measurements, although the statistical significance was weak.

Risk stratification for recurrent tachyarrhythmias in patients with paroxysmal atrial fibrillation and flutter: role of signal averaged electrocardiogram and echocardiography.

The value of signal-averaged P-wave electrocardiogram and echocardiography for predicting recurrent atrial tachyarrhythmias was prospectively investigated in 60 patients presenting with paroxysmal atrial fibrillation or flutter. All patients were followed up for 1 year after restoration of sinus rhythm. A stepwise discriminant function analysis was used to identify variables predicting recurrent atrial tachyarrhythmias. Analyzed variables included signal-averaged P-wave duration in 3 bipolar orthogonal leads (X,Y,Z) and their vector magnitude, as well as left and right atrial dimensions and volumes. During follow-up, 25 patients had recurrent atrial tachyarrhythmias, while 35 did not. Using discriminant function analysis, the left atrial antero-superior dimension was found to be the only variable predicting the recurrence of atrial tachyarrhythmias (p < 0.0038) and was able to correctly classify 65% of the study patients. It was concluded that, in patients with paroxysmal atrial fibrillation or flutter, the traditionally used determination of left atrial dimension was the variable most closely associated with a high risk for recurrent tachyarrhythmias. The signal-averaged P-wave duration did not improve tachyarrhythmia prediction.

Signal averaged P wave compared with standard electrocardiography or echocardiography for prediction of atrial fibrillation after coronary bypass grafting.

OBJECTIVE: To define the clinical value of the signal averaged P wave (SAPW) and to compare it with the standard electrocardiogram (ECG), echocardiogram, and clinical assessment for the prediction of...

Contribution of Left Atrial Pressure and Dimension to Signal-Averaged P-Wave Duration in Patients With Chronic Congestive Heart Failure

In a group of patients with chronic heart failure, a longer P-wave duration on signal-averaged electrocardiogram was found in those patients with higher pulmonary capillary wedge pressure, whereas the left atrium end-systolic diameter was not significantly different. Furthermore, an acute reduction in pulmonary capillary wedge pressure induced by sodium nitroprusside infusion was associated with a reduction in P-wave duration.

Frequency Analysis of the P Wave: Comparative Techniques

Frequency domain analysis of the signal-averaged P wave (SAPW) may provide additional information over time domain analysis in patients with paroxysmal atrial fibrillation (PAF), but an optimum method has not yet been defined. We compared two different approaches using SAPW and test signals. We analyzed the frequency spectrum of the entire P wave (method A) or of only its terminal 100 msec (method B) using SAPW from 24 patients with idiopathic PAF and 34 normal controls. Absolute powers in frequency bands above 20, 30, 40, 60, and 80Hz (P20, P30, P40, P60, and P80) and power ratios about these frequencies (PR20, PR30, PR40, PR60, and PR80) were calculated. Patients had greater P30, P60, and P80 using method A (P30: 28.6 [+/- 2.2] vs 22.8 [+/- 1.6] microV2.s; P = 0.04; P60: 4.7 [+/- 0.5] vs 3.4 [+/- 0.3] microV2.s; P = 0.03; P80: 1.9 [+/- 0.2] vs 1.3 [+/- 0.09] microV2.s; P = 0.01) but differences were smaller with method B. Moving the P wave endpoint 10 msec into the P wave had no effect on frequency domain parameters using method A but produced important changes using method B. Both methods were also applied to test signals of different durations but equal powers and power ratios. Method A gave predicted values for power and PR40 at all signal durations, but method B produced variable results. Frequency domain analysis of the SAPW shows significant increases in P wave energy in patients with PAF compared to controls. Analysis of the entire P wave is influenced less by signal duration and variations of the P wave endpoint than analysis of the terminal P wave alone and may define patient and control populations more precisely.

1025-100 Patients with WPW Syndrome and Paroxysmal Atrial Fibrillation Shows Prolonged Atrial Conduction Time by Signal-Averaged P-Wave Electrocardiogram

The purpose of this study was to establish a relationship between the atrial activation assessed by signal-averaged P wave ECG (SAPW) and episodes of paroxysmal atrial fibrillation (PAF) in patients (pts) with WPW syndrome (WPWS). fourteen pts with documented episodes of PAF, without underlying heart disease were selected (12 men: age = 35.2 ± 11.1 years) from a total of 70 consecutives pts successfully submitted to radiofrequency catheter ablation of accessory pathway (AP). All pts with anterograde conduction over the AP. left side AP in 9 pts and right side AP in 5 pts. The SAPW were recorded with the Corazonix Predictor II system from the X, Y, Z leads (40–250 Hz, least Square filter, final noise &lt; 0.3 μV). The total filter P wave duration (PWD) was obtained manually from the vector-magnitude in ms. Recordings were performed between 7 th and 14 th day after the ablation. No pts showed left atrial larger than 4.0 cm on the echocardiogram. The results were compared with a control group of 12 pts matched in age (5 men; age = 33.0 ± 10.2 years) without heart disease. Values were given as mean and 1SO and compared using non-paired Student t test (significance &lt; 0.05). Control Group In = 12): PWD ranged from 115.0 to 129.5 ms with a mean of 124.4 ± 4.4 ms. WPWS with PAF (n = 14): PWD ranged from 130.0 to 171.0 ms with a mean of 142.9 ± 1 0.1 ms (p &lt; 0.000). Eleven pts (78.5%) showed PWD &gt; 135.0 ms. There were no differences between PWD and AP location. Recurrent PAF after ablation was noted in 3 pts (21% – PWD: 171.0, 1505 and 139.0 ms for each patient). With a cutoff &lt; 135.0 ms for a normal PWD, the sensitivity was 78.5%, the specificity was 100%; the positive predictive value was 100% and the negative was 75% for SAPW to identify pts with WPWS and PAF. In the current study, pts with WPWS and PAF showed prolonged intra-atrial conduction time when compared with a control group. This may contribute to the development of PAF.

Correlation of Signal‐Averaged P Wave with Electrophysiological Testing for Atrial Vulnerability in Strokes of Unexplained Etiology

Atrial fibrillation is considered the main cause of cardioembolic strokes. After detailed investigations, about 30% of ischemic strokes remain unexplained. A percentage of these ischemic attacks may result from asymptomatic episodes of paroxysmal atrial fibrillation (PAF). Previous studies have demonstrated that electrophysiological testing and signal-averaged P wave (SAPW) ECG are useful to detect patients with PAF. Twenty patients with unexplained ischemic strokes had electrophysiological studies (EPS) to determine atrial vulnerability and SAPW recordings. At EPS, patients were classified in group I (10 patients) if they had a latent atrial vulnerability index < 2 and/or more than 1 minute of sustained atrial arrhythmia. Otherwise they were classified in group II (10 patients). In group I, the filtered P wave duration was greater: 142 versus 120 msec (P = 0.03) and RMS 30 tended to be lower: 2.54 versus 4.13 microV (P = 0.11) than in group II. A filtered P wave duration > 125 msec associated with a RMS 30 < 3 microV had a positive predictive value of 78% and a negative predictive value of 88% for the detection of patients with abnormal atrial vulnerability at EPS. SAPW may be useful to identify patients at risk of PAF who may be candidates for EPS.

Automatic analysis of high resolution atrial activation in mitral valve stenosis

High resolution P-waves of 28 patients having a mean age of 45 years and affected by isolated mitral valve stenosis (nine of whom showed paroxysmal atrial fibrillation) have been compared with those obtained from 30 healthy subjects about 35 years old. Our primary aim was to characterize the signal-averaged P-wave in mitral valve stenosis. Parameters which differed between the two groups in time domain analysis were the P-wave duration, the abscissa of the maximum positive voltage amplitude, the peak-to-peak amplitude and the integrated voltage-time product, which turned out to be greater in the patient class than in the healthy set; furthermore, in the frequency domain analysis, amplitudes in the range from 37 to 60 Hz were greater in healthy subjects than in patients. A successive analysis carried out to predict those patients with mitral valve stenosis who are at risk of developing paroxysmal atrial fibrillation showed that the P-wave duration and the amplitudes (in the range 60–106 Hz) were the most distinctive parameters, but, unfortunately, without any significant difference with respect to those of patients with mitral valve stenosis alone. Finally, some correlations between the age, the P-wave duration and the left atrial diameter of patients, were revealed to exist only in patients affected by episodes of atrial fibrillation.

Study and significance of triggered signal-averaged P-wave in hypertension

Study and significance of triggered signal-averaged P-wave in hypertension

Analysis of the signal-averaged P-wave duration in patients with percutaneous coronary angioplasty-induced myocardial ischemia

To assess the impact of angioplasty-induced myocardial ischemia on the duration of the surface P wave, patients undergoing elective angioplasty of isolated lesion in the left anterior descending, circumflex or right coronary arteries were monitored with a 3-channel electrocardiographic Holter system. The leads used were modified bipolar chest leads V 5, aVF and V 2 (CM-V 5, CS-aVF and CMV 2). After electrocardiographic signal-averaging, the earliest onset and the latest offset of the P wave were identified in all of the above timealigned signal-averaged leads, and the composite maximal P duration was measured under 10 X magnification. The maximal ST-segment shift during balloon inflation was also measured in all of the above leads at 60 ms after the J point. In the study group comprising 47 patients, the mean signal-averaged P-wave duration was 125.0 ± 16 ms at baseline versus 130.0 ± 15 ms during balloon inflation, p < 0.005. In the left anterior descending coronary artery group (n = 23), the mean signalaveraged P-wave duration was 122.4 ± 17 ms and 131.3 ± 16 ms during balloon inflation, p < 0.005. In the group with a right coronary artery lesion (n = 18), the values were 127.3 ± 14 ms and 128.4 ± 13 ms respectively (p = not significant). Significant increases in the P-wave duration were found to occur in groups both with (n = 34) and without (n = 13) ST-segment shift ≥1 mm (both p < 0.05). Thus, the duration of the signalaveraged surface P wave is prolonged during angioplasty-induced ischemia, but significantly so only in the group with left anterior descending coronary artery occlusion.