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 atrial fibrillation after coronary bypass grafting (CABG). Design-Prospective validation cohort study. Setting-Regional cardiothoracic centre. Patients-201 unselected patients undergoing first elective CABG were recruited over six months. Patients requiring concomitant valve surgery were excluded. Main outcome measures-Age, sex, cardiothoracic ratio, and cardioactive drugs were noted. P wave specific SAPW recordings, ECG, and M mode echocardiograms from which left atrial diameter was measured were performed within 24 hours of surgery. Filtered P wave duration (SAPWD), spatial velocity, and energy were calculated from the SAPW. From the ECG, lead II P wave duration, P terminal force in lead Vl, total P wave duration, and isoelectric interval were measured. Patients had Holter monitoring for 48 hours postoperatively and daily ECGs until discharge.Results-Two patients died (1%) and 10 were unsuitable for analysis (5%). Of the remaining 189, 51 (27%) had atrial fibrillation (AF) lasting > 1 hour at a mean of 2 (0.5 to 7) days after CABG. Of the variables examined, only SAPWD (AF group 148 (SD 12), v 142 (14) ms, P = 0-008) and male sex (AF group 96%, v 78%, P < 0.01) were significantly different. A prospectively defined SAPWD of > 141 ms predicted atrial fibrillation with positive and negative predictive accuracies of 34% and 83%. Logistic regression analysis identified both male sex and SAPWD as significant independent predictors of postoperative atrial fibrillation. Conclusions-Signal averaged P wave duration was a better predictor of atrial fibrillation after coronary bypass grafting than standard electrocardiographic or echocardiographic criteria. The predictive value of this test is such that it is likely to be useful in the design of prospective trials of prophylactic antiarrhythmic treatment but is of limited use using current techniques in the clinical management of individual patients.

Objective-To assess the reproducibility of time and frequency domain variables derived from the signal averaged P wave. Design-Longitudinal within patient study. Setting-Regional cardiothoracic centre. Patients-20 patients (10 with documented paroxysmal atrial fibrillation and 10 normal controls) were studied on three occasions to assess the reproducibility of repeated signal averaged P wave recordings. Digital P wave recordings were made on a further 10 patients on a single occasion and the recordings signal averaged twice in order to assess the reproducibility of the averaging system itself in the absence of biological variation. Main outcome measures-P wave duration, spatial velocity, and energies contained in frequency bands from 20, 30, and 60-150 Hz of the P wave spectrum were measured after P wave specific signal averaging. Coefficients of reproducibility were calculated for paired signal averaged P waves derived by signal averaging the same digital recordings on two separate occasions, for recordings performed in the same patients immediately after each other ("back to back") and those performed one week apart. Results-System reproducibility when the same digital P wave recordings were signal averaged on two separate occasions was high (< 11% for all variables). For P wave duration the coefficient of reproducibility was 11-4% for back to back recordings and 13-1% for those one week apart. The reproducibility of spatial velocity and P wave energy was low. Variation in P wave morphology was noted when successive P waves from the same subject were examined. If recordings with the same P wave morphology were analysed the reproducibility of spatial velocity and P wave energy improved but remained significantly poorer than that for P wave duration. Conclusions-P wave duration is reproducible within subjects in the short and medium term. Frequency domain and spatial velocity analysis are poorly reproducible, due more to spontaneous variation in P wave morphology than to instability of the signal averaging process. This may limit the utility of signal averaged P wave variables other than duration for the prediction of atrial arrhythmia.

Recent research suggests that the dispersion of QT intervals across 12 leads of the standard electrocardiogram (ECG) is a clinically important indicator of the susceptibility of patients to serious ventricular arrhythmias. This hypothesis can be further tested by measuring E C G from large clinical trials in which outcome is known for each patient. These ECGs are stored on paper. We have developed a system which scans ECG waveforms stored on paper, ana' converts them to digital data stored on computer. The system which incorporates a user-interface, enables quick and reliable measurements of QT intervals, thereby replacing the tedious and potentially insensitive method of hand measurements. Preliminary results of comparison between hand and user-interactive measurements are presented to show the accuracy and characteristics of the system.

Intra-vascular Doppler catheters are becoming popular as research tools for studies of the coronary circulation. Velocity estimates can be obtained from Doppler signals sampled with such catheters, and used to calculate various derived parameters which can then be correlated with the haemodynamic situation under investigation. This note discusses the requirements necessary for a system to perform the acquisition of the high-frequency Doppler signals obtained from catheter-tipped transducers, and a system developed to capture, process and store Doppler, ECG and pressure signals is described. Software used to calculate parameters from the stored waveforms is discussed and examples of the system outputs presented.

No abstract