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Notes: Background: P wave signal-averaged electrocardiography (PW-SAECG) is a new method that is proving to be an accurate and independent noninvasive marker for the risk of developing atrial fibrillation. This article presents current data acquisition and analysis techniques for PW-SAECG. It also discusses in detail the interplay of inherent challenges present in the morphological attributes of the P wave, and how correct technique can play a large role in surmounting these challenges, thereby producing good results.Methods: Proper patient preparation and correct configuration of instrument settings ensure accurate P wave detection and alignment during the signal-averaging process. This in turn preserves waveform integrity of the resulting signal-averaged P wave data. Subsequent application of appropriate filtering schemes and signal processing methods permit the calculation and analysis of key PW-SAECG time-domain parameters.Conclusions: Judicious modification of established data acquisition protocols from R wave signal averaging, coupled with appropriate postprocessing and analysis techniques, are necessary precursors for arriving at acceptable time-domain PW-SAECG results.

Notes: Background: Atrial fibrillation (AF) is a commonly encountered arrhythmia following cardiac surgery and when sustained, may be associated with significant morbidity.Methods: This large prospective investigation examined a variety of clinical and P wave signal-averaged electrocardiogram (SAECG) parameters to identify independent predictors of AF following cardiac surgery. A total of 272 patients underwent P wave SAECG recording and analysis prior to surgery. Information on their clinical, surgical, and hemodynamic characteristics as well as hospital course was collected. Patients were followed during their postoperative course with telemetry and ECGs.Results: During an observation period of up to 14 days, 79 patients (29%) developed AF 2.5 ± 1.9 days after surgery. Patients who developed AF following cardiac surgery were more likely to be older, undergo valve surgery, to have ejection fraction (EF) 〈 40%, to have P wave duration on SAECG 〉140 ms (all P 〈 0.01), and to take digoxin preoperatively (P 〈 0.05). A multivariate analysis found that only P wave duration on SAECG 〉140 ms and EF 〈 40% were independent predictors of AF following cardiac surgery. The odds ratio of P wave duration on SAECG 〉140 ms and EF 〈 40% for the development of AF following cardiac surgery was 3.1 and 2.8, respectively, and 8.7 when combined.Conclusions: Thus, the presence of preexisting abnormal atrial substrate as detected by P wave prolongation on SAECG, and implicated by EF 〈 40%, clearly predicted a higher risk of AF following cardiac surgery and may provide clinicians with an effective means of identifying those at greatest risk.

Notes: BackgroundAtrial fibrillation is the most common arrhythmia encountered in clinical practice. Identification of factors predisposing to atrial fibrillation may have implications for its prevention and may facilitate the detection of patients most susceptible to atrial fibrillation and its sequelae. Prolongation of P wave duration representing intra-atrial conduction delay is inadequately visualized in a standard electrocardiogram. Accurate detection, alignment, amplification and filtering of P waves during the signal averaging process permits a better analysis of the P wave and thus atrial conduction. Signal averaged P wave electrocardiography is a noninvasive technique that has permitted the evaluation of patients at risk of developing atrial fibrillation. Several studies have correlated the abnormalities in signal averaged P wave with paroxysmal atrial fibrillation, and have demonstrated its utility in independently predicting patients at risk of developing atrial fibrillation following cardiac surgery. New uses are likely to evolve as the technique is used clinically and as the methodology is standardized. A.N.E. 1999;4(4):401–407

Notes: Background: The effect of Ml on the high frequency content of the QRS complex in the SAECG remains a matter of controversy. The purpose of this study was (1) to characterize the changes in the high frequency QRS energy that occur after experimental Ml in dogs, (2) to evaluate the change in QRS energy in a number of frequency bandwidths, and (3) to evaluate the relationship between the change in QRS energy and infarct size and location, as well as the inducibility of VT.Methods: MIs were created in 21 dogs by balloon occlusion of the left circumflex (n = 10) or left anterior descending (n = 11) coronary arteries. SAECGs, using three orthogonal leads (X, Y, Z), were obtained before and 4–6 days after the Ml. The vector magnitude was calculated. Using a spectral filter, we calculated the energy in û Vs) of the entire QRS as the integrated area of the signal voltage within a low frequency bandwidth (15–40Hz) and two high frequency bandwidths (40–80 Hz, 80–300 Hz). QRS energy was log transformed to achieve a normal distribution.Results: There was a significant decrease in QRS energy after Ml in the low and high frequency bandwidths in the 21 dogs that was primarily detected in the Y lead. This decrease in high frequency energy after Ml occurred primarily in the dogs with anterior infarction where there was a 13–21% drop in QRS energy in all three bandwidths in the vector magnitude as well as the Y and Z leads (all P 〉 0.05). This drop in QRS energy after anterior wall Ml was moderately correlated with increasing infarct size in all three bandwidths. There were no consistent changes in QRS energy in the dogs with posterior infarction. The drop in QRS energy after Ml was not associated with inducible VT. The change in QRS energy after Ml in all three bandwidths were highly correlated.Conclusions: The process of Ml produced a decrease in QRS energy, in both low and high frequency bandwidths, that was most consistent in dogs with anterior wall Ml. The decrease in QRS energy after Ml was not associated with inducible VT. Ml produced similar changes in QRS energy in low and high frequency bandwidths. A.N.E. 1999;4(1):72–82

Notes: Background: We have previously demonstrated that high frequency QRS energy decreases after experimental myocardial infarction (Ml) and is lower in patients who have had MI compared to controls. The mechanism for this decrease in high frequency QRS energy is unclear. The objective of this study was to evaluate the effect of slowed myocardial conduction on high frequency QRS energy measured on the signal-averaged SAECG. We hypothesized that slowed conduction in the infarcted ventricle may be responsible for the decrease in high frequency QRS energy. In order to test this hypothesis, we examined antiarrhythmic drug therapy known to slow conduction (propafenone) compared to drug therapy with minimal effects on conduction (sotalol).Methods: In patients with sustained ventricular tachyarrhythmias undergoing serial drug testing, SAECGs were obtained before and after antiarrhythmic therapy. After filtering the leads with a spectral band-pass (15–40 Hz, 40–80 Hz, and 80–300 Hz) filter, the vector magnitude was con structed, and the energy (in μV sec) was calculated for the entire QRS by integrating the area under the filtered QRS complex.Results: Propafenone significantly prolonged QRS duration (+17%, P 〉 0.001) and significantly reduced QRS energy (-16.1% to 21.8%, P 〉 0.0001) in all three band widths. Sotalol did not have either effect (P = ns). There was a strong correlation between the prolongation of the filtered QRS and the drop in QRS energy for all three band widths (r values ranging from 0.64–0.90, all P 〉 0.05). When the changes in QRS energy were corrected for QRS duration, the results did not change.Conclusion: The Class IC antiarrhythmic drug propafenone, known to decrease myocardial conduction velocity, significantly reduced QRS energy in all three band widths, whereas the Class III drug sotalol did not. These data are consistent with the hypothesis that decreases in low and high frequency QRS energy after Ml result in part from slowed conduction.

Notes: Background: The signal-averaged electrocardiogram (SAECG) is a useful noninvasive diagnostic tool for assessing delayed ventricular activation.Methods: The advantage of the SAECG over standard ECGs the ability to detect very low amplitude signals indicative of areas of slowed myocardial conduction, a requirement for reentrant arrhythmias.Results: The SAECG has been proven useful in a variety of clinical situations, particularly in risk stratification after myocardial infarction or in the patient with dilated cardiomyopathy, and in screening for the need for electrophysiological studies in the syncope patient or the patient with nonsustained ventricular tachycardia.Conclusions: This review focuses on the currently accepted methodology of the time-domain SAECG, and outlines the standard applications of the SAECG based on the results of important clinical research.

Notes: While abnormalities in the P wave SAECG have been associated with the occurrence of AF, its reproducibility has never been documented. The purpose of this study was to evaluate the immediate and short-term reproducibility of measurements from the P wave SAECG. P wave SAECGs were obtained using well-described techniques that utilize the QHS complex as the trigger and the P wave as template for averaging. In 28 subjects (8 controls, 11 with cardiac disease, 9 with prior AF), 3 P wave SAECGs were obtained: an initial study; an immediate reacquisition; and reacquisition after 4–5 days. Vector duration and RMS voltage of the terminal 20 ms of the P wave SAECG were measured and compared. The mean P wave duration was 152 ± 14 ms on initial SAECG, 152 ± 14 ms and 152 ± 15 ms at immediate and short-term reacquisitions, respectively (both P = NS vs initial). The mean terminal BMS voltage was 6.4 ± 6.0 mcV on initial SAECG, 6.4 ± 5.9 mcV and 6.5 ± 5.8 meV at immediate and short-term reacquisitions, respectively (both P = NS vs initial). Linear regression analysis showed high reproducibility for both P wave duration (r = 0.94 for immediate and r = 0.96 for short-term reacquisition vs initial) but slightly less for terminal RMS voltage (r = 0.92 for immediate and r = 0.84 for short-term reacquisition vs initial). In subgroup analysis, P wave duration measurements were highly reproducible in controls, in subjects with cardiac disease, and in those with a history of AF. P wave duration was also reproducible for both males and females, as well as for subjects age 〉 65 years (r = 0.96 and 0.89 for immediate and short-term reacquisition, respectively). Terminal RMS voltage measurements were reproducible for controls, but less reproducible in other subgroups. In conclusion, P wave duration measurements on SAEGG are reproducible when evaluated at immediate and short-term reacquisition regardless of age, sex, cardiac disease, or prior AF. Terminal RMS voltages were less reproducible, especially in patients with cardiac disease and/or prior AF. These findings may explain conflicting observations regarding the clinical utility of terminal P wave measurements.

Notes: Ablation and Coagulation Activation. Introduction: Although thromboembolism is an uncommon complication of radiofrequency (RF) ablation, some preliminary reports have suggested that RF ablation results in activation of the coagulation system, possibly increasing this risk. We hypothesized that the insertion of intravenous catheters and their prolonged intravenous placement rather than RF ablation activates the coagulation cascade. Methods and Results: Thirty-seven patients, group 1 (n = 21) during RF ablation, and group 2 (n = 16) during routine electrophysiologic studies (EPS), were studied prospectively. Blood was drawn for coagulation and fibrinolytic studies following insertion of venous sheaths (TO), following catheter placement (T1), and 1 hour after completion of RF ablation or EPS {T2). Conversion of prothrombin to thrombin was measured using thrombin-antithrombin complex (TAT) and prothrombin activation peptide (F1+2). and fibrinolytic activity was assessed using D-dlmer concentration. Levels of D-dimer increased in group 1 from 823.52 ± 323.52 ng/mL at TO to 1,314.28 ± 297.63 ng/mL at T2 (P= 0.005), and in group 2 from 658.15 ± 161.70 ng/mL at T0 to 1625 641.45 ng/mL at T2 (P=±0.064). TAT levels increased from to 27.74 ± 5.6 μg/L at T0 to 52.99 ± 5.93 μg/L at T2 in group 1 (P= 0.09), and from 19.79 ± 5.14 μg/L at T0 to 73.5 ± 24.15 μg/L at T2 in group 2 (P= 0.05). F1+2 concentration increased from 1.52 ± 0.30 nmol/L at T0 to 3.06 ± 0.41 nmol/L at T2 in group 1 (P= 0.004), and from 1.32 ± 0.30 nmol/L at T0 to 3.11 ± 0.46 nmol/L at T2 in group 2 (P= 0.087). There was no significant difference in the concentration of the three coagulation variables between group 1 and group 2 at any given time point. No correlation was demonstrable between concentration of D-dimers, TAT, or F1+2 and variables of RF delivery such as cumulative energy, number of RF energy applications, or number of impedance rises. However, a significant positive correlation (r = 0.65, P 〈 0.01) was noted between the duration of the RF ablation procedure and the concentration of D-dimers. Conclusion: We conclude that activation of the coagulation cascade in RF ablation procedures is not related to the delivery of RF energy, but is related to the placement of intravascular catheters and to the duration of the ablation procedure.

Notes: Update on SAECG. The signal-averaged electrocardiogram (SAECG) facilitates noninvasive recording of low-amplitude cardiac signals such as ventricular late potentials. The SAECG has been used to accurately predict life-threatening ventricular tachyarrhythmias in patients after acute myocardial infarction and with nonischemic dilated cardiomyopathy, and to screen for inducible ventricular tachycardia in patients with unexplained syncope and with nonsustained ventricular tachycardia. This review focuses on currently accepted methodology and clinical and research applications of the SAECG.

Notes: Depression and reduced sexual functioning have been identified as problems following ICD placement. We examined these issues, and multiple other quality-of-life measures, and their relationship to ICD and ICD discharge. Patients were 64 ± 11 years old, 72% male, and had undergone ICD 20 ± 14 months previously. Fifty-eight patients responded to a confidential biopsychosocial questionnaire. Positive attitudes toward the procedure increased from 52% before to 76% after implantation. Satisfaction correlated most strongly with less anger (P = 0.002, r = 0.45), less worry about ICD size (P = 0.007, r = 0.38), less sadness (P = 0.01, r = 0.37), and perceived better health (P = 0.01, r = 0.35). Of these ICD patients, 20%–58% reported measures of depression, and sexual frequency was reduced in 45%. Despite successful ICD placement, health concern increased in 62 % of the respondents. Thirty-nine percent attended support groups; 96% found them very helpful. Mean number of ICD discharges described by responders was 5 ± 11. Fifty percent of our sample reported ≥ 1 shock; equal numbers had 1, 2–5, 6–10, and more than 10 shocks. Sixty-two percent of men had at least one discharge compared to 13% of women. After controlling for cardiac clinical variables, experiencing ≥ 1 ICD shock was strongly associated with anxiety about family (odds ratio = 7.3), reduced new activities (odds ratio = 6.9), increased sadness (odds ratio = 6.2), and health worry (odds ratio = 5.8). Experiencing ≥ 5 ICD shocks was strongly associated with increased health concern (odds ratio = 13.6), increased sadness (odds ratio = 12.5), increased fatigue (odds ratio = 6.1), current sadness (odds ratio = 5.8), and increased nervousness (odds ratio = 5.3). ICD implantation powerfully affects quality-of-life. Postimplantation health concern is paradoxically increased despite improvement in actual health. Negative emotions are associated with defibrillator discharge.