Signal-averaged P-wave duration and risk of paroxysmal atrial fibrillation in hyperthyroidism

Triad of palpitation, angina, and murmur in a non-cardiac patient

The triad of palpitation, angina, and murmur is a classical feature of cardiac pathology. However, their presence sometimes uncovers a thyroid etiology. Identification well in time decreases out-of-pocket expenditures on illness and suffering. We report a case of a 40-year-old woman who presented with fever with chills, vomiting, palpitations, and shortness of breath for the past month. Also, she described chest pain as typical of angina. Multiple diagnoses were made elsewhere, but none of the treatments resulted in the resolution of symptoms. ST changes were suggestive of ischemic pathology, cardiac MRI done showed up hypertrophied myocardium. After a negative blood culture for infective endocarditis and serology sought for fever work-up, suspicious cardiac examination with a murmur, and an abnormal thyroid profile with a thyroid scan, led to a diagnosis of Graves' disease. This case defines the triad in a noncardiac patient and emphasizes what a thyroid disease does to the heart.

Assessing Atrial Fibrillation Substrates by P Wave Analysis: A Comprehensive Review

Atrial fibrillation (AF) is the most common cardiac arrhythmia. Pharmacologic and non-pharmacologic rhythm control strategies impact on AF-related symptoms, while leaving largely unaffected the risk of stroke. Moreover, up to 20% of AF patients are asymptomatic during paroxysmal relapses of arrhythmia, thus underlying the need for early markers to identify at-risk patients and prevent cerebrovascular accidents. Indeed, non-invasive assessment of pre-clinical substrate changes that predispose to AF could provide early identification of at-risk patients and allow for tailored care paths. ECG-derived P wave analysis is a simple-to-use and inexpensive tool that has been successfully employed to detect AF-associated structural and functional atrial changes. Beyond standard electrocardiographic techniques, high resolution signal averaged electrocardiography (SAECG), by recording microvolt amplitude atrial signals, allows more accurate analysis of the P wave and possibly AF risk stratification. This review focuses on the evidence that support P wave analysis to assess AF substrates, predict arrhythmia relapses and guide rhythm-control interventions.

Screening strategies for atrial fibrillation: a systematic review and cost-effectiveness analysis

Background

Atrial fibrillation (AF) is a common cardiac arrhythmia that increases the risk of thromboembolic events. Anticoagulation therapy to prevent AF-related stroke has been shown to be cost-effective. A national screening programme for AF may prevent AF-related events, but would involve a substantial investment of NHS resources.

Objectives

To conduct a systematic review of the diagnostic test accuracy (DTA) of screening tests for AF, update a systematic review of comparative studies evaluating screening strategies for AF, develop an economic model to compare the cost-effectiveness of different screening strategies and review observational studies of AF screening to provide inputs to the model.

Design

Systematic review, meta-analysis and cost-effectiveness analysis.

Setting

Primary care.

Participants

Adults.

Intervention

Screening strategies, defined by screening test, age at initial and final screens, screening interval and format of screening {systematic opportunistic screening [individuals offered screening if they consult with their general practitioner (GP)] or systematic population screening (when all eligible individuals are invited to screening)}.

Main outcome measures

Sensitivity, specificity and diagnostic odds ratios; the odds ratio of detecting new AF cases compared with no screening; and the mean incremental net benefit compared with no screening.

Review methods

Two reviewers screened the search results, extracted data and assessed the risk of bias. A DTA meta-analysis was perfomed, and a decision tree and Markov model was used to evaluate the cost-effectiveness of the screening strategies.

Results

Diagnostic test accuracy depended on the screening test and how it was interpreted. In general, the screening tests identified in our review had high sensitivity (> 0.9). Systematic population and systematic opportunistic screening strategies were found to be similarly effective, with an estimated 170 individuals needed to be screened to detect one additional AF case compared with no screening. Systematic opportunistic screening was more likely to be cost-effective than systematic population screening, as long as the uptake of opportunistic screening observed in randomised controlled trials translates to practice. Modified blood pressure monitors, photoplethysmography or nurse pulse palpation were more likely to be cost-effective than other screening tests. A screening strategy with an initial screening age of 65 years and repeated screens every 5 years until age 80 years was likely to be cost-effective, provided that compliance with treatment does not decline with increasing age.

Conclusions

A national screening programme for AF is likely to represent a cost-effective use of resources. Systematic opportunistic screening is more likely to be cost-effective than systematic population screening. Nurse pulse palpation or modified blood pressure monitors would be appropriate screening tests, with confirmation by diagnostic 12-lead electrocardiography interpreted by a trained GP, with referral to a specialist in the case of an unclear diagnosis. Implementation strategies to operationalise uptake of systematic opportunistic screening in primary care should accompany any screening recommendations.

Limitations

Many inputs for the economic model relied on a single trial [the Screening for Atrial Fibrillation in the Elderly (SAFE) study] and DTA results were based on a few studies at high risk of bias/of low applicability.

Future work

Comparative studies measuring long-term outcomes of screening strategies and DTA studies for new, emerging technologies and to replicate the results for photoplethysmography and GP interpretation of 12-lead electrocardiography in a screening population.

Study registration

This study is registered as PROSPERO CRD42014013739.

Funding

The National Institute for Health Research Health Technology Assessment programme.

Advanced glycation end products (AGEs) and its receptors in the pathogenesis of hyperthyroidism

Oxidative stress has been implicated in the pathogenesis of hyperthyroidism and its complications. Interaction of advanced glycation end products (AGEs) with receptor RAGE (receptor for AGEs) generates reactive oxygen species. Soluble receptor for AGEs (sRAGE) competes with RAGE for binding with AGEs and attenuates the generation of ROS. Low levels sRAGE and high levels AGEs would generate more ROS leading to hyperthyroidism and its complications. The objectives are to determine if levels of serum sRAGE are low and the levels of AGEs and AGEs/sRAGE are high in patients with hyperthyroidism. The study subjects comprised of 33 patients with hyperthyroidism and 20 controls. Levels of serum sRAGE were lower, while that of AGEs and AGEs/sRAGE were higher in patients compared to controls, being significant only for sRAGE and AGEs/sRAGE. When the levels of sRAGE, AGEs, and AGEs/sRAGE were assessed for hyperthyroidism associated with different diseases, the levels of sRAGE were lower in Hashimoto disease, and levels of AGEs were higher in patients with Graves' disease compared to control. The levels of AGEs/sRAGE were elevated in an all except patients with Hashimoto disease. The levels of AGEs, sRAGE, or AGEs/RAGE were not correlated with age, weight, and blood pressures except systolic pressure which was inversely correlated with sRAGE. The levels of sRAGE were negatively correlated with AGEs and AGEs/sRAGE. The levels of AGEs/sRAGE were positively correlated with AGEs. In conclusion, low levels of sRAGE, and high levels of AGEs and AGEs/sRAGE are risk biomarkers in the pathogenesis hyperthyroidism and its complications.

Effects of mineralocorticoid receptor antagonist spironolactone on atrial conduction and remodeling in patients with heart failure

BACKGROUND

Spironolactone was shown to reduce mortality in patients with heart failure (HF). However, the effect of spironolactone on the incidence of atrial fibrillation remains unknown. Therefore, we examined the effects of spironolactone on atrial conduction and remodeling in patients with HF.

METHODS AND RESULTS

A total of 21 patients with HF were divided into either spironolactone group (n=11) or control group (n=10). The patients were followed up for 12 months. Blood examination, echocardiogram, and signal-averaged electrocardiogram were performed at study enrollment and after 3 and 12 months of treatment. In the spironolactone group, atrial natriuretic peptide tended to reduce, left atrium dimension was significantly smaller, the ratio of E wave to A wave tended to improve, and P-duration was significantly shortened.

CONCLUSIONS

Spironolactone improves atrial conduction and remodeling in patients with HF.

Evaluation of the relationship between atrial septal aneurysm and cardiac arrhythmias via P-wave dispersion and signal-averaged P-wave duration

OBJECTIVE

The aim of the study was to investigate the relationship between atrial septal aneurysms (ASAs) and cardiac arrhythmias via signal-averaged P-wave duration (SAPWD) and P-wave dispersion (Pd).

METHODS

Sixty-six patients with ASA served as the study group (group 1; 28 men and 38 women; mean age, 34 +/- 10 years) and 62 healthy volunteers served as the control group (group 2; 29 men and 33 women; mean age, 31 +/- 8 years) in the current study. ASAs were diagnosed by transthoracic echocardiography based on the criteria of a minimal aneurysmal base of > or =15 mm; and an excursion of > or =10 mm. All subjects were evaluated by 24-hour Holter monitoring, 12 lead body surface electrocardiogram for P-wave analysis, and signal-averaged electrocardiogram for P-wave duration (PWD).

RESULTS

There was no significant difference between the study and control groups in terms of age, gender, left atrium diameter, and left ventricular ejection fraction. Supraventricular arrhythmias (SVAs) were detected in 29 patients with ASA (43.9%) and 5 controls (8.1%; P < 0.001). The mean Pd in patients with ASA was significantly longer compared to the control group (14.1 +/- 8 ms vs 7.0 +/- 2.9 ms; P < 0.001). Similarly, the mean SAPWD in group 1 was significantly longer compared to group 2 (127.4 +/- 17.6 ms vs 99.8 +/- 12.3 ms; P < 0.001).

CONCLUSION

Prolonged SAPWD and Pd were determined to indicate electrical disturbances in the atrial myocardium, and predict the increase in the prevalence of SVA in patients with ASA.

P-wave dispersion in endogenous and exogenous subclinical hyperthyroidism

BACKGROUND

The aim of this study was to measure maximum P wave duration (Pmax) and P wave dispersion (PWD), which can be indicators for the risk of paroxysmal atrial fibrillation when increased, and to reveal their relationship with thyroid hormone levels in patients with endogenous and exogenous subclinical hyperthyroidism.

METHODS

Seventy-one patients with sublinical thyrotoxicosis (34 endogenous, 37 exogenous) and 69 healthy individuals were enrolled in the study. Pmax and minimum P wave duration (Pmin) on electrocardiogram recordings were measured and PWD was calculated as Pmax-Pmin.

RESULTS

Pmax (p<0.001) and PWD (p<0.001) values were significantly higher in patients with endogenous subclinical hyperthyroidism compared with the control group. Pmax (p<0.001) and PWD (p<0.001) values were significantly higher in patients with exogenous subclinical thyrotoxicosis compared with the control group. Pmax (p=0.710) and PWD (p=0.127) were not significantly different in patients with endogenous subclinical hyperthyroidism compared with exogenous subclinical hyperthyroid patients. Pmax and PWD negatively associated with TSH in endogenous and exogenous subclinical hyperthyroidism.

CONCLUSION

In the present study, we observed that Pmax and PWD were longer in patients with endogenous and exogenous subclinical hyperthyroidism. Lack of a difference in Pmax and PWD between patients with endogenous and exogenous subclinical hyperthyroidism seems to support the idea that hormone levels rather than the etiology of thyrotoxicosis affect the heart.

Electrocardiographic predictors of atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is the most prevalent arrhythmia in the United States and accounts for more than 750,000 strokes per year. Noninvasive predictors of AF may help identify patients at risk of developing AF. Our objective was to identify the electrocardiographic characteristics associated with onset of AF.

METHODS

This was a retrospective cohort analysis of 42,751 patients with electrocardiograms (ECGs) ordered by physician's discretion and analyzed using a computerized system. The population was followed for detection of AF on subsequent ECGs. Cox proportional hazard regression analysis was performed to test the association between these ECG characteristics and development of AF.

RESULTS

For a mean follow-up of 5.3 years, 1,050 (2.4%) patients were found to have AF on subsequent ECG recordings. Several ECG characteristics, such as P-wave dispersion (the difference between the widest and narrowest P waves), premature atrial contractions, and an abnormal P axis, were predictive of AF with hazard ratio of approximately 2 after correcting for age and sex. P-wave index, the SD of P-wave duration across all leads, was one of the strongest predictors of AF with a concordance index of 0.62 and a hazard ratio of 2.7 (95% CI 2.1-3.3) for a P-wave index >35. These were among the several independently predictive markers identified on multivariate analysis.

CONCLUSIONS

Several ECG markers are independently predictive of future onset of AF. The P index, a measurement of disorganized atrial depolarization, is one of the strongest predictors of AF. The ECG contains valuable prognostic information that can identify patients at risk of AF.

Hyperthyroid heart disease

The heart is an organ sensitive to the action of thyroid hormone, and measurable changes in cardiac performance are detected with small variations in thyroid hormone serum concentrations. Most patients with hyperthyroidism experience cardiovascular manifestations, and the most serious complications of hyperthyroidism occur as a result of cardiac involvement. Recent studies provide important insights into the molecular pathways that mediate the action of thyroid hormone on the heart and allow a better understanding of the mechanisms that underlie the hemodynamic and clinical manifestations of hyperthyroidism. Several cardiovascular conditions and drugs can interfere with thyroid hormone levels and may pose a difficulty in interpretation of laboratory data in patients with suspected thyroid heart disease. The focus of this report is a review of the current knowledge of thyroid hormone action on the heart and the clinical and hemodynamic laboratory findings as well as therapeutic management of patients with hyperthyroid heart disease.

Prediction of Atrial Fibrillation with Atrial Late Potentials and Pathological Chemoreflexsensitivity

BACKGROUND

Atrial fibrillation (AF) is a very common arrhythmia that often causes the serious complication of a stroke.

OBJECT

The aim was to evaluate the utility of pathological chemoreflexsensitivity (PCHRS) and atrial late potentials (ALP) to predict AF in follow-up.

METHODS

We investigated a prospective study on the basis of our observation about a PCHRS and ALP in paroxysmal AF. The PCHRS was predefined as a chemoreflexsensitivity below 3.0 ms/mmHg and ALP were predefined as a filtered P-wave duration > or =120 ms and a root mean square voltage of the last 20 ms of the P-wave < or =3.5 microV. A P-wave triggered P-wave signal averaged electrocardiograph (ECG) and chemoreflexsensitivity was performed on 250 consecutive patients who were divided into four groups. Group I consisted of patients with ALP and PCHRS, patients of group II had only ALP, a PCHRS was only present in group III, and patients of group IV had neither ALP nor PCHRS.

RESULTS

During the mean follow-up of 37.8 months AF was observed in 10 patients (4%). The patients of the four groups were similar according to clinical baseline characteristics. The incidence of AF was higher in group I (18% of patients) than in group II (6% of patients, P = 0.229) and significantly higher than in group III (3% of patients, P = 0.034) or group IV (1% of patients, P < 0.0001). Patients with ALP and PCHRS showed a 33-fold risk (P < 0.001) for the onset AF.

CONCLUSIONS

The results of our study suggest that the probability of AF could be predicted with a P-wave signal averaged ECG and an analysis of chemoreflexsensitivity. The predictive power of the combination of ALP and PCHRS seemed not high enough for risk stratification.

Long-term prognostic value of p-wave characteristics for the development of atrial fibrillation in subjects aged 55 to 74 years at baseline

Atrial fibrillation (AF) is the most prevalent arrhythmia in the elderly, associated with high mortality and morbidity rates. Changes in electrocardiographic P waves were associated with AF in patient series, but the long-term prognostic value of P-wave characteristics in the development of AF was not shown. The aim was to evaluate P-wave duration and morphologic characteristics as potential independent risk markers for the long-term development of AF in the general population. A nested case-control design was adopted in subjects aged 55 to 74 years and apparently healthy at baseline. Baseline P-wave items of 40 patients who developed AF within the 10-year period were compared retrospectively with those of 120 matched controls. Broad maximum P waves (>/=120 ms) at baseline were observed in 70% of patients with AF and 41% of controls (p = 0.002). Maximum P-wave duration proved to be a significant risk marker independent of blood pressure, body mass index, and other electrocardiographic findings. However, this association seems overruled by the predictive value of morphologic changes defined as notched or deflected P waves (p = 0.0002). The joint occurrence of longer duration in combination with morphologic changes in the P wave proved a very important risk indicator for the development of AF over 10 years, with an adjusted odds ratio of 13.4 (95% confidence interval 3.3 to 46.6). In conclusion, enhanced clinical appreciation of P-wave items on the standard electrocardiogram at rest, preferably evaluated in all 12 leads, may help identify a group at high risk of the development of AF at an early stage.

Reverse Electrical Remodeling of the Atria Post Cardioversion in Patients Who Remain in Sinus Rhythm Assessed by Signal Averaging of the P-Wave

OBJECTIVES

This study was designed to determine whether the signal-averaged electrocardiogram of the P-wave (SAPW) is an independent predictor of recurrence of atrial fibrillation (AF) post cardioversion (CV), and to assess atrial remodeling using SAPW.

BACKGROUND

There are limited electrophysiologic data to predict the recurrence of AF post-CV. The electrical remodeling that occurs post-CV is poorly understood.

METHODS

Sixty-four patients with persistent AF undergoing CV were prospectively enrolled. SAPW parameters were measured the day of CV and repeated at 1 month. These SAPW parameters were compared to other baseline indices for the recurrence of AF.

RESULTS

Sixty patients (94%) had successful CV. At 1 month, 22 (37%) maintained sinus rhythm (SR). The SAPW total duration decreased significantly in those who remained in SR (159 ms +/- 19 to 146 ms +/- 17; P < 0.0001). Only the duration of AF (46 +/- 50 days vs 147 +/- 227 days, P = 0.03) and the presence of left ventricular hypertrophy (LVH, 12% vs 65%, P = 0.0006) were significantly associated with recurrence of AF. Atrial size strongly correlated with the SAPW duration in patients who remained in SR (R(2)= 0.67, P = 0.003) but not in those who returned to AF (R(2)= 0.11, P = 0.65).

CONCLUSIONS

Atrial electrical reverse remodeling occurs in patients with AF who maintain SR post-CV. This remodeling is likely inversely related to the duration of AF and LVH. SAPW duration does not predict recurrence of AF post-CV.

Optimal P-wave duration for bedside diagnosis of interatrial block

BACKGROUND

Interatrial block (IAB; P wave > or = 110 ms) is highly prevalent and associated with atrial tachyarrhythmias, left atrial electromechanical dysfunction and is a potential risk for embolism. Investigators have often used different parameters for P-wave duration to define IAB, and this causes confusion further adding to clinician ignorance of IAB. We therefore appraised the mode P-wave duration in IAB and evaluated the sensitivity and specificity of using previously used durations.

METHODS

We prospectively evaluated 225 electrocardiograms (ECGs) of patients at a tertiary care general hospital for P-wave duration. Of these, 49 were excluded because of severe motion artifact, errors in lead placement, absence of adequate patient identification, and atrial flutter or fibrillation. Mean, standard error of mean (SEM), standard deviation (SD), mode P-wave duration, specificity, and sensitivity were calculated of the remaining 176 ECGs.

RESULTS

From the sample (N = 176; ages 15-95 years; mean +/- SD = 69.15 +/- 16.53 years, female 50.3%), measured P-wave durations ranged from 50 ms to 230 ms (mean +/- SD = 113.75 +/- 30.56 ms, SEM 2.30 ms). 96 patients (54.55%) showed IAB (P wave > or = 110 ms) with the mode P-wave duration being 120 ms. Sensitivity and specificity of using P wave > or = 110 ms is 100% and 88.9%, respectively (accuracy 94.31%), while P wave > or =130 ms yielded 64% and 100%, respectively (accuracy 82.38%).

CONCLUSIONS

Mode P-wave duration in IAB is 120 ms, and thus, for all practical reasons, it may be used to clinically diagnose IAB using ECGs recorded at the bedside at 25 mm/s with 10 mm/mV standardization.

Circadian behavior of P-wave duration, P-wave area, and PR interval in healthy subjects

BACKGROUND

The prolongation of P-wave duration has long been shown to indicate the presence of high risk for atrial fibrillation. The circadian variation of P-wave characteristics and their dynamic adaptation to heart rate changes was not tested before.

METHODS

To evaluate the diurnal pattern of P-wave duration, P area, and PR interval and of their linearly fitted relation with RR interval, 50 healthy volunteers (25 men, mean age 34 +/- 10 years) underwent 24-hour ambulatory electrocardiographic (ECG) recording with digital 12-lead Holter recorders. The median P-wave duration, P area, and PR interval were calculated from the average 12-lead ECG constructed from each 10-second ECG recording. Single harmonic regression analysis was performed to reveal the presence of circadian variation in the aforementioned ECG parameters.

RESULTS

The P area (P < 0.0001, R(2) = 0.78), the PR interval (P < 0.0001, R(2) = 0.92), the P area / RR slope (P < 0.0001, R(2) = 0.55), and the PR/RR slope (P < 0.0001, R(2) = 0.42) showed a highly significant circadian variation while the periodic nature of P-wave duration (P = 0.016, R(2) = 0.32) and of the P duration / RR slope (P = 0.011, R(2) = 0.18) was only indicated by harmonic regression analysis.

CONCLUSIONS

P-wave duration, P area, and PR interval show a significant circadian variation in healthy subjects. The relations between P area/RR,PR/ RR, and P duration/RR also demonstrate a significant diurnal pattern.

The Bachmann Bundle and interatrial conduction

The cardiac conduction system (CCS) is responsible for generation and systematic conduction of cardiac impulses. The Bachmann Bundle (BB), considered one of its several accessory impulse-conducting pathways, plays a fundamental role in interatrial conduction. Delay in this pathway leads to prolongation of the P wave on the electrocardiogram (interatrial delay or block), which in turn is a precursor for atrial tachyarrhythmias, mainly atrial fibrillation and significant left atrial electromechanical dysfunction. As such, the magnitude of its sequelae has necessitated a flurry of investigations that have been targeted toward its prevention and management. Although current studies on the use of angiotensin-converting enzyme inhibitors and atrial pacing have indeed shown some promise, it would be shortsighted to overlook and circumvent the actual underlying lesion-BB abnormality. Thus, a thorough understanding of the CCS and interatrial conduction is essential. We review current literature on the BB and discuss potential mechanisms that affect its conduction.

Prediction of the recurrence of atrial fibrillation after cardioversion in the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) study

BACKGROUND

The early recurrence of atrial fibrillation (AF) after cardioversion and the need for frequent cardioversions to maintain sinus rhythm are important clinical features of AF management.

METHODS

We evaluated patients in the AFFIRM study whose qualifying episode of AF lasted > or = 48 hours and was terminated by cardioversion. Clinical, electrocardiographic, and echocardiographic risk factors associated with AF recurrence within 2 months of cardioversion and > or = 2 cardioversions during the first year were identified using multivariate analysis in 1293 eligible patients.

RESULTS

The risk factors for the recurrence of AF within 2 months of cardioversion were no coronary artery disease and an electrocardiographic lead II P-wave duration of > 135 milliseconds. In the subset of patients not taking antiarrhythmic drug therapy, the multivariate risk factors were no coronary artery disease, second or greater episode of AF, left ventricular ejection fraction < 0.50, and mitral valve thickening. Significant risk factors for the need for > 2 cardioversions in the first year in patients taking antiarrhythmic medication were left atrial diameter > 4.5 cm and mitral valve thickening. The overall sensitivity and specificity of these parameters for recurrence and repeated cardioversion are low.

CONCLUSION

There are several risk factors for difficulty maintaining sinus rhythm after cardioversion of persistent AF. The clinical predictive value of these factors is low, and they probably should not be used to justify withholding rhythm control efforts in patients who might benefit from sinus rhythm.

Simple electrocardiographic markers for the prediction of paroxysmal atrial fibrillation in hyperthyroidism

BACKGROUND

Hyperthyroidism is a major cause of paroxysmal atrial fibrillation (AF). The purpose of this study was to evaluate the predictors of AF in the patients with clinical and subclinical hyperthyroidism.

METHODS AND RESULTS

The study population consisted of four groups: group I (57 euthyroid healthy persons), group II (33 patients with subclinical hyperthyroidism), group III (69 patients with overt hyperthyroidism) and group IV (31 patients with overt hyperthyroidism and documented paroxysmal AF). The maximum P wave duration (P maximum) in group IV (114 +/- 8 ms) was significantly higher than group I (102 +/- 7 ms, p < 0.001), group II (106 +/- 7 ms, p < 0.001) and group III (108 +/- 9 ms, p0.005). The P wave dispersion (PWD) was measured as 46 +/- 9 ms in group IV and this was significantly higher than group I (29 +/- 8 ms, p < 0.001), group II (36 +/- 9 ms, p < 0.001) and grup III (38 +/- 8 ms, p = 0.001). The P maximum and PWD were higher in the patients with subclinical hyperthyroidism compared to healthy individuals. Univariate regression analysis revealed that age, P maximum and PWD, multivariate analysis showed that P maximum and PWD were significant predictors of paroxysmal AF. A PWD value of 37.5 ms separated group IV from others with a sensitivity of 90%, specificity of 85%, and positive predictive accuracy of 77%.

CONCLUSION

Simply measuring P maximum and PWD values, we could identify the patients with high risk for the development of AF and these simple ECG parameters may help in clinical judgement to determine the requirement for treatment in the patients with subclinical hyperthyroidism.

The signal-averaged P-wave duration is longer in hypertensive patients with history of paroxysmal atrial fibrillation as compared to those without

BACKGROUND

Onset of atrial fibrillation in hypertensive patients is usually associated with a high occurrence of cardiovascular complications. Therefore, it is important to assess non-invasively the risk of developing paroxysmal atrial fibrillation (PAF) in hypertensive patients during sinus rhythm. This study was undertaken to determine if hypertensive patients with history of PAF could be identified while in sinus rhythm by measurement of signal-averaged ECG P-wave duration.

METHODS

Signal-averaged electrocardiography (SAECG) P-wave recording was performed in 44 hypertensive patients (30 men and 14 women; mean age 60+/-11 years, group A) who had a history of paroxysmal AF and in 50 hypertensive patients without history of AF (33 men and 17 women; mean age 57+/-12, group B). All patients were also evaluated by using echocardiography to measure left ventricular ejection fraction (LVEF) and left atrial diameter (LAD).

RESULTS

SAECG P-wave duration was found to be significantly higher in group A than in group B (146+/-14 ms vs. 128+/-11 ms, p<0.001). Left atrial diameter was not significantly different (40.1+/-3.4 mm vs. 39.3+/-3.0 mm, p>0.05), whereas LVEF was significantly lower in group A than group B (63+/-5% vs. 67+/-4%, p=0.03). There was a correlation between SAECG P-wave duration and age (r=0.32, p<0.05). In univariate analysis, SAECG P-wave duration and LVEF were significant predictors of PAF, but only SAECG P-wave duration remained a significant independent predictor of PAF in multivariate analysis.

CONCLUSION

The results of this study indicate that hypertensive patients with history of PAF can be detected while in sinus rhythm by signal-averaged ECG P-wave duration.

Reversal of Electrical Remodeling After Cardioversion of Persistent Atrial Fibrillation

INTRODUCTION

In animals, atrial fibrillation results in reversible atrial electrical remodeling manifested as shortening of the atrial effective refractory period, slowing of intra-atrial conduction, and prolongation of sinus node recovery time. There is limited information on changes in these parameters after cardioversion in patients with persistent atrial fibrillation.

METHODS AND RESULTS

Thirty-eight patients who had been in atrial fibrillation for 1 to 12 months underwent electrophysiologic testing 10 minutes and 1 hour after cardioversion. At 1 week, 19 patients still in sinus rhythm returned for repeat testing. Reverse remodeling of the effective refractory period was not uniform across the three atrial sites tested. At the lateral right atrium, there was a highly significant increase in the effective refractory period between 10 minutes and 1 hour after cardioversion (drive cycle length 400 ms: 204 +/- 17 ms vs 211 +/- 20 ms, drive cycle length 550 ms: 213 +/- 18 ms vs 219 +/- 23 ms, P < 0.001). The effective refractory period at the coronary sinus and distal coronary sinus did not change in the first hour but had increased by 1 week. The corrected sinus node recovery time did not change in the first hour but was shorter at 1 week (606 +/- 311 ms vs 408 +/- 160 ms, P = 0.009). P wave duration also was shorter at 1 week (135 +/- 18 ms vs 129 +/- 13 ms, P = 0.04) consistent with increasing atrial conduction velocity.

CONCLUSION

The atrial effective refractory period increases, sinus node function improves, and atrial conduction velocity goes up in the first week after cardioversion of long-standing atrial fibrillation in humans. Reverse electrical remodeling of the effective refractory period occurs at different rates in different regions of the atrium.

Detection of patients with hypertrophic cardiomyopathy at risk for paroxysmal atrial fibrillation during sinus rhythm by P-wave dispersion

BACKGROUND

Paroxysmal atrial fibrillation (PAF) in hypertrophic cardiomyopathy (HCM) is associated with poor prognosis. Previous studies have shown good correlation between P-wave dispersion (Pd) and occurrence of PAF. However, Pd in patients with HCM for predicting PAF has not been studied.

HYPOTHESIS

The aim of the study was to determine whether Pd could identify patients with HCM who are likely to suffer from PAF.

METHODS

Twenty-two patients with HCM with a history of PAF (Group 1) and 26 patients with HCM without a history of PAF (Group 2) were studied. Maximum (Pmax) and minimum (Pmin) P-wave durations, as well as P-wave dispersion (Pd = Pmax - Pmin) were calculated from 12-lead surface electrocardiograms (ECG).

RESULTS

P-wave dispersion was significantly different between the groups (Group 1: 55 +/- 6 ms vs. Group 2: 37 +/- 8 ms; p<0.001), while Pmax (Group 1: 134 +/- 11 ms vs. Group 2: 128 +/- 13 ms; p = 0.06) and Pmin (Group 1: 78 +/- 9 ms vs. Group 2: 81 +/- 7 ms; p = 0.07) was not significantly different. Patients with a history of PAF had higher left atrial diameter than the patients without PAF (Group 1: 52 +/- 8 mm vs. Group 2: 48 +/- 10 mm; p = 0.02). A cut-off value of 46 ms for Pd had a sensitivity of 76% and a specificity of 82% in discriminating between patients with and without PAF.

CONCLUSION

This study suggests that P-wave dispersion could identify patients with HCM who are likely to develop PAF.

Electrophysiologic predictors of the recurrence of persistent atrial fibrillation within 30 days of cardioversion

Patients with recurrence of persistent atrial fibrillation within 30 days of cardioversion had slower atrial conduction, a slower sinus rate, no difference in the absolute value of the effective refractory period, greater early reverse remodeling of the effective refractory period, and more premature atrial contractions than those who did not. These findings highlight the role of slow conduction and premature atrial contractions in the pathophysiology of atrial fibrillation and suggest a possible proarrhythmic effect of reverse remodeling.

Duration of the P wave and P wave dispersion in subclinical hyperthyroidism

OBJECTIVE

To determine whether the values for P wave dispersion (Pdis) and adjusted Pdis, which are simple noninvasive electrocardiographic markers to detect paroxysmal atrial fibrillation, differ in patients with endogenous subclinical hyperthyroidism in comparison with those in healthy control subjects.

METHODS

We measured the maximal P wave duration and the difference between the maximal and the minimal P wave duration (Pdis) from the 12-lead surface electrocardiogram of 36 patients with endogenous subclinical hyperthyroidism and of 22 age- and sex-matched healthy control subjects. Adjusted Pdis (Pdis/square root of the number of measured electrocardiographic leads) was also calculated from each electrocardiogram.

RESULTS

The minimal P wave duration was significantly shorter in patients with subclinical hyperthyroidism than in healthy control subjects (P<0.001). Pdis and adjusted Pdis were also significantly higher in the patient group than in the control subjects (P<0.05). By univariate analysis, only thyrotropin levels were found to be associated with adjusted Pdis (r = -0.28; P = 0.03).

CONCLUSION

Pdis and adjusted Pdis differed in patients with endogenous subclinical hyperthyroidism in comparison with those values in healthy control subjects. Thus, these simple electrocardiographic markers may be useful for identifying patients with endogenous subclinical hyperthyroidism who are at risk for paroxysmal atrial fibrillation.

P wave analysis indices in young healthy men: data from the digital electrocardiographic study in Hellenic Air Force Servicemen (DEHAS)

P wave analysis from the 12-lead ECG is a recent contribution of noninvasive electrocardiology. P wave analysis indices (maximum and minimum P wave duration, P wave dispersion [Pdis = Pmax-Pmin], adjusted P wave dispersion [APdis = Pdis/square root of measured leads], summated P wave duration [Psum], standard deviation of P wave duration [Psd], mean P wave duration [Pmean]) can predict atrial arrhythmias. However, the definitions of all these indices are based on few studies. The aim of this analysis was to define normal values of these indices and the examine possible associations between P wave indices and clinical variables. The study included 1,353 healthy men, 24 +/- 3 years of age, who answered a questionnaire and underwent a detailed physical examination and a digitized 12-lead surface ECG. All P wave indices were analyzed by two independent investigators. Mean values of the ECG indices were: Pmax: 96 +/- 11 ms, Pmin: 57 +/- 9 ms, Pdis: 38 +/- 10 ms, Psum: 924 +/- 96 ms, Psd: 12 +/- 3, APdis: 11 +/- 3 ms, and Pmean: 77 +/- 8 ms. Age was significantly related with Pmax (r = 0.277, P < 0.01), Pmin (r = 0.255, P < 0.001), Psum (r = 0.074, P < 0.01), and Pmean (r = 0.074, P < 0.01). All ECG indices were significantly associated with the R-R interval, and among each other. This study defined normal indices of wave duration and correlations among them. These markers may play an important predictive role in patients with atrial conduction abnormalities.

A novel algorithm for cardiac biosignal filtering based on filtered residue method

In this paper, a new algorithm is presented for the filtering (de-noising) of cardiac bioelectrical signals. The primary target of this algorithm is the class of cardiac action potentials recorded using voltage-sensitive dyes, although the method is also applied to electrocardiographic signals. High periodicity is one of the main features of cardiac biosignals. The proposed algorithm exploits this feature in filtering signals with a minimum amount of distortion. The basic idea is to use signal averaging in time to find the stationary portion of the signal. The residue is found by subtracting the signal average from the corresponding points of the input. After passing through a low-pass filter, the filtered residue (FR) is added back to the signal average to reconstruct the output. The practical implementation of the filter residue algorithm is discussed. Stretching and shrinking operations are the basis for the conversion of quasi-periodic signals into periodic signals, which can then be subjected to the FR algorithm. Various examples are presented, and error estimation is performed to guide the selection of optimal parameters for the algorithm. The ability of the algorithm to reconstruct the variation among beats is demonstrated, and its limitations are discussed.

Determination of risk for atrial fibrillation utilizing precise P wave duration-measuring methodology

Increased duration of the P wave has been shown to be an indicator of increased risk for atrial fibrillation. This paper describes a method of obtaining the "true P wave duration" from previously recorded six-channel electrocardiograms, using readily available personal computers and software instead of more expensive P wave signal averaging devices. P wave duration in the atrial fibrillation group was significantly greater than in the nonfibrillation group. Measuring true P wave duration has greater sensitivity and specificity than measuring "conventional P wave duration." Precise measurement of P wave duration may prove to be an important factor in determining the risk of atrial arrhythmias. (c) 2001 by CHF, Inc.

Clinical and electrocardiographic predictors of recurrent atrial fibrillation

Patients with frequent episodes of paroxysmal atrial fibrillation (AF) are prone to develop permanent AF and have an increased thromboembolic risk. We have previously shown that P wave dispersion (P dispersion), defined as the difference between the maximum and the minimum P wave duration, and maximum P wave duration (P maximum) can distinguish patients with paroxysmal lone AF. The ability of those ECG markers and of other clinical and ECG variables to detect patients at risk for recurrent AF was tested in 88 patients, aged 64 +/- 12 years. All patients had a history of symptomatic episodes of AF during the last 2 years and had not previously received any antiarrhythmic prophylaxis. P maximum and P dispersion were calculated from a 12-lead surface ECG recorded in all patients during sinus rhythm. A computerized ECG system was used and P maximum and P dispersion were calculated on screen from the averaged complexes of all 12 leads. Age (P = 0.01), history of organic heart disease (P = 0.03), P maximum (P < 0.001), minimum P wave duration (P = 0.05), and P dispersion (P < 0.001) were found to be significant univariate predictors of recurrent AF, whereas only P maximum (P < 0.001) and age (P = 0.037) remained significant independent predictors of frequent AF paroxysms in the multivariate analysis. It is concluded that advanced age and prolonged P wave duration may be used as predictors of frequently relapsing AF. Therefore, simple AF predictors exist that could possibly distinguish the patients in whom prophylaxis with antiarrhythmic medicines should be instituted.

Comparison of different methods for manual P wave duration measurement in 12-lead electrocardiograms

To determine whether different methods for the manual measurement of P wave duration are mutually consistent, we evaluated the intraobserver and interobserver errors of P wave measurements obtained in three different ways: (1) by cursor on a high resolution computer screen (on screen), (2) by calipers and a magnifying glass (on paper), and (3) by a high resolution digitizing board (on board). The agreement between the methods was assessed in 30 normal subjects and 30 patients with a history of atrial fibrillation. The maximum P wave duration (P maximum), the minimum P wave duration (P minimum), mean P wave duration (P mean), P wave dispersion (P dispersion = P maximum - P minimum), and the standard deviation of the P wave duration in all measured leads (P SD) were calculated from a 12-lead electrocardiogram in each subject. Only P maximum, P mean, and P dispersion were significantly higher in patients than in controls with all three methods. Intraobserver and interobserver relative errors were significantly different among the three methods; the lowest errors were associated with the on-screen measurement. The agreement between the three different methods was acceptable for P maximum, P mean, and P SD and rather poor for P minimum and P dispersion in both groups. The differences of the measurement by different methods did not consistently differ between the two groups. Hence, the on-screen measurements are consistent with other manual methods and provide more stable results. Manual measurement of ECG patterns should be preferably performed with digital ECG recordings displayed on a high resolution computer screen.

Prediction of atrial fibrillation recurrence after cardioversion by P wave signal-averaged electrocardiography

The purpose of this report was to determine prospectively whether P wave signal-averaged electrocardiography (ECG) is useful for the prediction of recurrences of atrial fibrillation after cardioversion. The P wave signal-averaged ECG was recorded in 73 patients after successful cardioversion. Duration of the filtered P wave and the root mean square voltages for the last 20 ms of the P wave were calculated. In addition to signal-averaged ECG P wave analysis, all patients were evaluated by echocardiography. During 6 months follow-up period recurrence of atrial fibrillation was observed in 31 (42.5%) patients and in 42 (57.5%) patients sinus rhythm was maintained. There was no difference in gender, age, presence of organic heart disease, left atrial diameter, left ventricular ejection fraction, use of antiarrhythmic drug, and duration of atrial fibrillation (P>0.05). The filtered P-wave duration was longer and the root mean square voltages for the last 20 ms of the P wave was lower in patients with recurrence of atrial fibrillation than in patients who maintained sinus rhythm (138.3+/-12.5 ms vs. 112.4+/-11.8 ms, P = 0.001; 1.9+/-0.7 microV vs. 2.5+/-0.6 microV, P = 0.001). A filtered P-wave duration > or =128 ms associated with a root mean square voltage for the last 20 ms of the P wave < or =2.1 microV had a sensitivity of 70% and specificity of 76% for the detection of patients with recurrence of atrial fibrillation after successful cardioversion of atrial fibrillation. We found that the likelihood of recurrence of atrial fibrillation after cardioversion was increased 4.31-fold (95% confidence interval 2.08-9.83) if these parameters were used. These results suggest that P wave signal-averaged ECG could be useful to identify patients at risk for recurrence of atrial fibrillation after cardioversion.

Dispersion of filtered P wave duration by P wave signal-averaged ECG mapping system: its usefulness for determining efficacy of disopyramide on paroxysmal atrial fibrillation

INTRODUCTION

Although it is desirable to know drug efficacy before initiating antiarrhythmic therapy, there have been no methods for this evaluation. P wave signal-averaged ECG (P-SAECG) is useful to detect subtle changes in disturbance of atrial conduction. The purpose of this present study was to test whether P-SAECG mapping system would give any information on the efficacy of disopyramide on the prevention of paroxysmal atrial fibrillation (PAF).

METHODS AND RESULTS

P-SAECG was performed before disopyramide treatment, at 3 hours after a single dose of oral disopyramide (200 mg), and after 4 weeks of disopyramide treatment (300 mg/day). After measuring the filtered P wave duration by the vector magnitude and mapping methods, we calculated filtered P wave duration dispersion, difference between the maximal and minimal filtered P wave duration within 16 chest leads at these three time points. Filtered P wave duration and filtered P wave duration dispersion before treatment were longer in 32 patients with symptomatic PAF than in 31 healthy volunteers. Disopyramide was effective for suppression of PAF in 17 patients and ineffective in 15 patients after 4 weeks of treatment. Filtered P wave duration was similarly prolonged at 3 hours in the two groups, whereas filtered P wave duration dispersion at 3 hours after the disopyramide administration behaved differently; it decreased in all of the effective group and increased in all of the ineffective group. The effective patients were prospectively followed with the same treatment for 6 months. In 16 (94%) of these 17 effective patients, no PAF was documented and they remained to be asymptomatic.

CONCLUSIONS

Thus, measuring filtered P wave duration dispersion with the P-SAECG mapping method after a single administration may predict the long-term efficacy of disopyramide in patients with PAF.

Tachycardia-induced changes in Na+ current in a chronic dog model of atrial fibrillation

We have previously shown that chronic rapid atrial activation (400 bpm) reduces atrial conduction velocity in dogs, contributing to the development of a substrate supporting sustained atrial fibrillation (AF). However, the cellular and ionic mechanisms underlying these functional changes have not been defined. We applied whole-cell patch-clamp techniques to atrial myocytes from dogs subjected to atrial pacing at 400 bpm for 7 days (P7, n = 6) and 42 days (P42, n = 5) and compared the results with those from sham-operated dogs similarly instrumented but without pacemaker activation (P0, n = 6). Rapid atrial pacing allowed for the induction of sustained AF in 67% and 100% of dogs paced for 7 and 42 days, respectively, and significantly decreased conduction velocity under P7 and P42 conditions. In dogs paced for 7 days, Na+ current (INa) density was reduced by 28% at -40 mV (P < .0001, n = 59 cells). INa changes were even more decreased under P42 conditions, by approximately 52% at -40 mV (P < .0001): from -78.7 +/- 4.6 pA/pF (P0, n = 28 cells) to -37.7 +/- 3.0 pA/pF (P42, n = 43 cells). INa was significantly reduced at all voltages ranging from -65 to -10 mV. Voltage-dependent activation and inactivation properties, activation kinetics, and recovery from inactivation were not altered by rapid atrial pacing; however, inactivation kinetics were slowed. AF duration was related to mean INa in each dog (r2 = .573, P < .001). We conclude that rapid atrial activation significantly reduces both conduction velocity and INa density. Since INa is a major determinant of conduction velocity, our data point to INa reduction as a potentially important mechanism contributing to the substrate for AF in this model.

Signal-averaged P wave in patients with paroxysmal atrial fibrillation

The theoretical and experimental rational of atrial signal-averaged ECG in patients with AF is delay in the intra-atrial and interatrial conduction. Similar to the ventricular signal-averaged ECG, the atrial signal-averaged ECG is an averaging of a high number of consecutive P waves that match the template created earlier P wave triggering is preferred over QRS triggering because of more accurate aligning. However, the small amplitude of the atrial ECG and its gradual increase from the isoelectric line may create difficulties in defining the start point if P wave triggering is used. Studies using P wave triggering and those using QRS triggering demonstrate a prolonged P wave duration in patients with paroxysmal AF. The negative predictive value of this test is relatively high at 60%-80%. The positive predictive value of atrial signal-averaged ECGs in predicting the risk of AF is considerably lower than the negative predictive value. All the data accumulated prospectively on the predictive value of P wave signal-averaging was determined only in patients undergoing coronary bypass surgery or following MI; its value in other patients with paroxysmal AF is still not determined. The clinical role of frequency-domain analysis (alone or added to time-domain analysis) remains undefined. Because of this limited knowledge on the predictive value of P wave signal-averaging, it is still not clinical medicine, and further research is needed before atrial signal-averaged ECG will be part of clinical testing.

Risk for atrial fibrillation in patients with hypertrophic cardiomyopathy assessed by signal averaged P wave duration

OBJECTIVE

To assess the relation between P wave duration and the occurrence of atrial fibrillation in hypertrophic cardiomyopathy (HCM).

DESIGN

High resolution signal averaged electrocardiography was used in 110 patients with HCM to determine whether patients at risk for paroxysmal atrial fibrillation could be detected during sinus rhythm by measuring P wave duration. Filtered P wave duration was measured manually, over an average of 300 beats per patient.

RESULTS

During follow up, 18 patients (16%) had at least one one clinical episode of paroxysmal atrial fibrillation, including four patients whose initial episode followed the signal averaged electrocardiogram. The 18 patients with overt atrial fibrillation had greater P wave duration than the 69 patients who did not develop atrial fibrillation: 150 (SD 20) v 126 (14) ms; P < 0.001. Another 23 patients without clinically evident atrial fibrillation had prolonged bursts of the arrhythmia on Holter recording, and showed a P wave duration (138 (15) ms) intermediate between patients with and without clinical atrial fibrillation. In assessing risk for atrial fibrillation, P wave duration > or = 140 ms was associated with sensitivity, specificity, and positive predictive accuracy values of 56%, 83%, and 66%. Multivariate analysis showed that duration of the P wave was the only independent variable associated with occurrence of atrial fibrillation; if P wave duration > or = 140 ms was combined with left atrial enlargement > 40 mm, the specificity and positive predictive accuracy for atrial fibrillation increased to 93% and 78%.

CONCLUSIONS

Measurement of P wave duration in sinus rhythm by high resolution signal averaged electrocardiography may be a useful non-invasive clinical tool for identifying patients with HCM likely to develop electrical instability and atrial fibrillation.

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.