P wave duration and morphology predict atrial fibrillation recurrence in patients with sinus node dysfunction and atrial-based pacemaker

P wave duration and morphology have never been systematically evaluated as markers of AF in patients with a conventional indication to pacing. This study correlated sinus P wave duration and morphology and the incidence of AF in patients with sinus node dysfunction (SND), previous history of AF before implant, and atrial-based pacemaker. Included were 140 patients (86 men, 54 women; mean age 71.8 +/- 10.4 years) with recurrent paroxysmal AF and who received a DDD (128 patients) or AAI (12 patients) pacemaker for SND. Forty-nine patients had structural heart disease. Sinus P wave duration and morphology was evaluated in leads II, III. Twenty-two patients had an abnormal P wave morphology, diphasic (+/-) in 5 and notched (+/+) in 17. The basic pacemaker rate was programmed between 60 and 70 beats/min. Rate responsive function was activated in 65 patients. During a follow-up of 27.6 +/- 17.8 months, AF was documented in 87 patients. Forty-four patients developed permanent AF, following at least one episode of paroxysmal AF in 26 cases. Statistical analysis used Cox model regression. Univariate predictors of AF (P < 0.10) were drugs (mean: 2 +/- 1.4) and DC shock before pacing (16/140 patients), P wave duration (mean 112.5 +/- 24.6 ms), basic pacemaker rate (mean 68 +/- 5 beats/min), and drugs in the follow-up (mean 1.2 +/- 0.94). Multivariate analysis showed that P wave duration (b = 0.013, s.e. = 0.004; P = 0.003), and drugs before pacing (b = 0.2; s.e. = 0.08; P < 0.01) resulted in a significant independent predictor of AF. Actuarial incidence of patients free of AF at 30 months was 35%: 56% in patients with a P wave < 120 ms, and 13% in those with P wave > or = 120 ms (P < 0.01 by Score test). Univariate predictors of permanent AF were drugs and DC shock before pacing, left atrial size (mean 39 +/- 6 mm), P wave duration, abnormal P wave morphology (22/140 patients), and drugs in the follow-up. Multivariate analysis showed that P wave morphology was the most important predictor of permanent AF (b = -0.56, s.e. = 0.2; P = 0.008). Incidence of patients free of permanent AF at 30 months was 69%: 74% in patients with normal P wave, compared to 28% in the case of abnormal P wave morphology (P < 0.01). P wave duration and morphology are good markers of postpacing AF recurrence in patients with SND and an atrial-based pacemaker. This observation suggests that intra- and interatrial conduction disturbances be extensively evaluated before implantation, and the indication for atrial resynchronization procedures be reevaluated.     

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.     

Predictive Value of the P Wave at Implantation for Atrial Fibrillation After VVI Pacemaker Implantation

This study assesses the value of P wave measurements on the surface EGG at implantation, in the prediction of atrial fibrillation in VVI paced patients. From a consecutive series of 320 pacemaker implantations 172 WI paced patients for symptomatic atrioventricular block (AVB) (n = 126; mean age 69 ± 14) or sick sinus syndrome (SSS) (n = 56; mean age 68,6 ± 12] and in sinus rhythm at implantation were used in this study. P wave duration in VI is correlated with the incidence of atrial fibrillation during 5 years of follow-up. VI at implantation was significantly longer (114.6 ± 2.7 msec) in the patients who developed atrial fibrillation than in those who did not (91.9 ± 2.7 msec) (P < 0.001). Although positive predictive accuracy increases progressively for higher VI values for AVB and SSS, the negative predictive and diagnostic accuracy of V1 criteria were Jess in SSS. Application of the Bayes' theorem showed that in SSS the probability to develop atrial fibrillation is 33% for V1 < 110 msec and is for V1 < 90 msec still higher than that reported in DDD paced patients. In the AVB group the probability to develop atrial fibrillation is 8% for V1 < 110 msec and 6% for V1 < 100 msec. It seems, therefore, that atrial stimulation (AAI or DDD) is always indicated in SSS. In AVB with V1 < 100 msec, DDD pacing, if not needed for other indications, apparently does not offer much benefit in the prophylaxis of atrial fibrillation.     

Is Dual Site Better Than Single Site Atrial Pacing in the Prevention of Atrial Fibrillation?

Long-term prevention of atrial fibrillation is not constantly realized by single-site right atrial pacing, and the beneficial role of multisite atrial pacing is still being studied. Accordingly, we compared the effectiveness of dual site and single site atrial pacing in 83 patients (50 men, 33 women, aged 69 +/- 10 years), who received a DDD device for primary sinus node dysfunction or bradycardia with documented atrial fibrillation. Inclusion criteria for dual site pacing were a sinus P wave > or = 120 ms and at least two episodes of documented paroxysmal AF in the 6 months preceding implantation. Dual site atrial pacing (high right atrium-coronary sinus ostium) was performed in 30 cases, and was compared to 53 single site paced patients, 21 with a P wave > or = 120 ms and 32 with a P wave < 120 ms. The basic pacing rate was programmed at 68 +/- 4 beats/min (range 60-75 beats/min). Sinus P wave (133 +/- 20 vs 95 +/- 9 ms; P < 0.001), paced P wave (107 +/- 14 vs 99 +/- 15; P < 0.05), number of antiarrhythmic drugs used (2.4 +/- 1.2 vs 1.6 +/- 1.5, P < 0.05), and the duration of symptoms (8.1 +/- 4.5 vs 3.8 +/- 2.4 years; P < 0.001) were significantly higher in dual site patients. The other characteristics were similar. During the follow-up of 18 +/- 15 months (range 3-30 months), paroxysmal AF was documented in 33 patients. Among these patients, 13 developed permanent AF following at least one episode of paroxysmal AF. When comparing dual site patients and single site patients with a P wave duration > or = 120 ms, paroxysmal AF incidence was lower in the dual site group (9/30 patients vs 15/21 patients, P < 0.01), as well as permanent AF (1/30 patients vs 8/21 patients, P < 0.01). By contrast, comparison between dual site patients and the group of single site patients with a P wave duration < 120 ms did not evidence any significant differences in paroxysmal (9/30 patients vs 9/32 patients) and permanent (1/30 patients vs 4/32 patients) AF incidences. Dual site seems better able than single site atrial pacing to improve the natural history of patients with a prolonged P wave, reducing the incidence of paroxysmal and permanent AF. No benefit could be expected in patients with a normal P wave duration.     

The acute effects of biatrial pacing on atrial depolarization and repolarization

Permanent biatrial and/or multisite atrial pacing may prevent atrial fibrillation (AF), but the effects on atrial electrophysiology remain incompletely understood. Acute biatrial pacing was studied in 20 patients with and 28 without (controls) a history of atrial fibrillation and/or flutter. Twelve-lead electrocardiograms were recorded during pacing from the high right atrium (RA), from the distal coronary sinus (LA), and biatrial pacing. P wave duration was measured in each lead and the difference between maximum and minimum P duration was termed P wave dispersion. Effective refractory periods (ERPs) were measured during each pacing mode. The dispersion of P wave duration was 35 +/- 14 ms in controls and 40 +/- 29 ms in AF patients (P = 0.17). Compared to RA pacing, LA pacing shortened P duration in controls (127 +/- 18 to 107 +/- 16 ms, P < 0.05) and biatrial pacing markedly shortened P duration in controls (127 +/- 18 to 93 +/- 14 ms, P < 0.05) and AF patients (114 +/- 43 to 97 +/- 21 ms, P < 0.05). P wave dispersion was unaffected. In controls, the LA ERP was longer than the RA ERP. This phenomenon was not present in AF patients, whose LA ERP was shorter than that of controls. Biatrial pacing had no effect on atrial ERPs or the dispersion of atrial refractoriness. In conclusion, acute biatrial pacing does not affect atrial repolarization but it does cause a marked shortening of global biatrial depolarization. Distal coronary sinus pacing produces a shorter P wave than RA pacing. There is substantial dispersion in the surface P wave of the electrocardiogram, the significance of which awaits further study.     

New onset of pacemaker dependency after permanent pacemaker implantation

Pacemaker dependency has dangerous consequences under conditions of electromagnetic interference, unrecognized lead dysfunction, and battery depletion, and has been associated with cardiovascular and overall mortality. The aim of this study was to examine the incidence of new onset of pacemaker dependency during long-term follow-up after pacing system implantation. The study included 518 patients (mean age 72.9 +/- 10.4 years) who presented with intrinsic rhythms at the time of implantation. Indications for pacing were sick sinus syndrome (SSS) in 275 (53%) patients, AV block in 209 (40%), and AF with bradycardia in 34 (7%) patients. The mean follow-up was 3.7 +/- 2.7 years (range 1-17). Pacemaker dependency was defined as the absence of an intrinsic rhythm during backup pacing at 30 beats/min for 30 seconds. New onset of pacemaker dependency was observed in 23 (4.4%) of the 518 patients at a mean of 3.1 +/- 2.7 years of follow-up. Pacing indications were SSS in 6 (2.2%) of 275 patients, AV block in 15 (7.2%) of 209, and AF with bradycardia in 2 (5.9%) of 34. Patients with AV block had a significantly higher incidence of pacemaker dependency than patients with SSS (odds ratio 3.51; 95% CI 1.3 to 9.3; P = 0.012). The average annual rate of new pacemaker dependency was 1.6% during an 8-year follow-up. The incidence of new onset of pacemaker dependency varied among pacing indications, and was significantly higher in patients with AV block than patients with SSS.     

Determining Optimal Atrial Sensitivity Settings for Single Lead VDD Pacing: The Importance of the P Wave Histogram

In order to provide atrioventricular synchrony, VDD pacing systems require reliable atrial sensing. Variations in atrial signals with exercise and daily activities may lead to undersensing, with loss of physiological pacing. The aim of this study was to determine, for a single lead VDD pacing system, the maximal variation in atrial signals in order to facilitate optimal programming of atrial sensitivity. Fifteen patients underwent implantation of a Vitatron Saphir VDD pacemaker with a Vitatron Brilliant electrode. At a mean (± SD) follow-up of 67.3 ± 38.8 days, resting P wave amplitude was compared with the P wave amplitude histogram obtained from the pacemaker, which recorded atrial signals over the preceding 30 days. Resting P wave amplitude was also compared with P wave amplitudes during variations in posture, respiration, and during exercise. P wave amplitude showed great variation with changes in posture and respiration, but there was no consistent increase or reduction. During exercise, the mean P wave amplitude fell hy 36.6%± 31.3% compared with the resting value (P < 0.05). During daily activities, 22.6% of P wave amplitudes recorded on the P wave histogram were < 0.5 mV. The smallest P wave amplitudes were detected by the P wave histogram in 11 (79%) of 14 patients. These data suggest that atrial sensitivity may need to be programmed higher than that indicated by single readings or exercise. The P wave amplitude histogram is the most reliable indicator of the smallest atrial signal and should be used to opthnize atrial sensitivity settings.     

Abnormal right atrial electrograms predict the transition to chronic atrial fibrillation in paced patients with sick sinus syndrome

Although pacing therapy for sick sinus syndrome (SSS) is established, the risk of developing chronic atrial fibrillation (CAF) makes pacing therapy infeasible in some patients. We evaluated whether electrophysiological characteristics of atrial muscle can serve as predictors of the transition to CAF after pacemaker implantation in patients with SSS. Eighty-nine patients with SSS underwent electrophysiological study before pacing therapy. Catheter mapping of 12 right atrial sites was performed during sinus rhythm during electrophysiological. An abnormal atrial electrogram was defined as having a duration of 100 ms or longer, or eight or more fragmented deflections, or both. Right atrial extrastimulation was also performed for atrial vulnerability. After electrophysiological study, all patients underwent pacemaker implantation and were followed up. During the follow-up period of 85 +/- 50 months, development of CAF was observed in 12 patients (group A). The remaining 77 patients remained in sinus rhythm (group B). There were significantly more abnormal atrial electrograms in group A than group B (2.7 +/- 2.3 vs 0.8 +/- 1.2; P < 0.001). The distribution of abnormal atrial electrograms was also greater in group A; patients in group A had more abnormal atrial electrograms than patients in group B in both the high and middle right atrium (P < 0.005 and P < 0.01, respectively). Kaplan-Meier analysis showed that almost 50% of the paced patients with abnormal atrial electrograms (n = 42) developed CAF (P < 0.005). Our data suggest that the existence of abnormal atrial electrograms is predictive of the transition to CAF in paced patients with SSS.     

Electrophysiological characteristics of the atrium in sinus node dysfunction with and without postpacing atrial fibrillation

In patients with sinus node dysfunction (SND) with or without associated paroxysmal atrial fibrillation (AF), the effectiveness of atrial pacing in reducing the incidence of AF is not definitive. In addition, despite several studies involving large populations of implanted patients, little attention has been paid to the electrophysiological (EP) atrial substrate and the effect of permanent atrial pacing. The aim of this study is to correlate EP data and the risk of AF after DDD device implantation. We reviewed EP data of 38 consecutive patients with SND, mean age 70 +/- 8 years, who were investigated free of antiarrhythmic treatment, for the evaluation of the atrial substrate. We also considered as control group 25 subjects, mean age 63 +/- 14 years, referred to our EP laboratory for unexplained syncope or various atrioventricular disturbances. Following pharmacological washout and at a drive cycle length of 600 ms, effective and functional refractory periods (ERP, FRP), S1-A1 and S2-A2 latency, A1 and A2 conduction duration, and latent vulnerability index (ERP/A2) were measured. AF induction was tested with up to three extrastimuli at paced cycle lengths of 600 and 400 ms in 20 patients. Induction of sustained AF (> 30 seconds) was considered as the endpoint. P wave duration on the surface ECG in lead II/V1 was also measured. DDD pacing mode was chosen in all patients with the minimal atrial rate programmed between 60 and 75 beats/min (mean 64 +/- 4 beats/min). After implantation, the patients were followed-up for 29 +/- 17 months and clinically documented occurrence of AF was determined. When comparing patients with SND and subjects of the control group, we did not find any significant statistical differences in terms of ERP (237 +/- 33 vs 250 +/- 29 ms), FRP (276 +/- 30 vs 280 +/- 32 ms) and S1-A1 (39 +/- 16 vs 33 +/- 11 ms) and S2-A2 latency (69 +/- 24 vs 63 +/- 25 ms). In contrast, we observed significant differences regarding A1 (55 +/- 19 vs 39 +/- 13 ms; P < 0.001), A2 (95 +/- 34 vs 57 +/- 18 ms; P < 0.001) and P wave duration (104 +/- 18 vs 94 +/- 15 ms; P < 0.05), and ERP/A2 (2.8 +/- 1.2 vs 4.8 +/- 1.6; P < 0.001). When comparing patients with (n = 11) or without (n = 27) postpacing AF occurrence, we did not find any difference with reference to ERP, FRP, S1-A1, S2-A2, A1 duration, or follow-up duration. In patients with postpacing AF occurrence, A2 was longer (116 +/- 41 vs 87 +/- 27 ms; P < 0.01), ERP/A2 lower (2.1 +/- 0.4 vs 3.1 +/- 1.4; P < 0.05), P wave more prolonged (116 +/- 22 vs 99 +/- 14 ms; P < 0.01), and preexisting AF history predominant (6/11 vs 5/27 patients; P < 0.05). No difference was observed between patients with (n = 8) and without (n = 12) AF induction during the EP study. In patients with SND, the atrial refractoriness appears normal and the most important abnormality concerns conduction slowing disturbances. Persistence of AF despite pacing stresses the importance of mechanisms responsible for AF not entirely brady-dependent. In this setting, more prolonged atrial conduction disturbances, responsible for a low vulnerability index, and a preexisting history of AF enable us to identify a high risk patient group for AF in the follow-up.     

Relationship between P-wave duration and atrial electromechanical delay assessed by tissue Doppler echocardiography

Background: The aim of the study was to assess the relationship between P‐wave duration on the surface electrocardiogram (ECG) and echocardiographic parameters of atrial electromechanical delay (EMD), as well as contraction synchrony during different atrial pacing modalities. Methods: In 57 patients with sinus node disease and prolonged sinus P‐wave duration treated with multisite atrial pacing (MSAp), the EMD was measured by tissue Doppler in several left and right atrial sites during sinus rhythm, MSAp, and single‐site pacing at right atrial appendage (RAAp), Bachmann's bundle (BBp) region, and coronary sinus (CSp) ostium. Regional atrial synchrony was calculated on the basis of EMD. Results: P‐wave duration was 141 ± 16, 120 ± 17, 138 ± 17, 144 ± 16, and 160 ± 19 ms during sinus rhythm, MSAp, BBp, CSp, and RAAp, respectively (P < 0.001 RAAp and MSAp vs other). P‐wave duration correlated with all atrial EMDs as well as interatrial and intraleft atrial parameters of dyssynchrony. In multivariate analysis, the EMD in lateral left atrial wall was the strongest predictor of P‐wave duration (β 0.41; P < 0.001). The relationship between P‐wave duration and the atrial EMDs was most prominent during RAAp (all left atrial walls r > 0.51; P < 0.01) and BBp (all atrial walls r > 0.42; P < 0.05), while during sinus rhythm and CSp, only weak correlation between echo and ECG was found. Neither of the tissue Doppler parameters correlated with P‐wave duration during MSAp. Interatrial dyssynchrony correlated with P‐wave duration during sinus rhythm and RAAp and intraleft atrial dyssynchrony only during sinus rhythm. Conclusions: P‐wave duration of the surface ECG is highly correlated with the atrial EMD, the relationship is specific for each pacing modality. (PACE 2011; 23–31)     

Predictors and clinical impact of atrial fibrillation after pacemaker implantation in elderly patients treated with dual chamber versus ventricular pacing

The Pacemaker Selection in the Elderly (PASE) trial was a prospective, multicenter, single blind, randomized comparison of single chamber, rate adaptive, ventricular pacing (VVIR) with dual chamber, rate adaptive pacing (DDDR) in 407 patients aged > or =65 years(mean 76 +/- 7 years, 60% male)with standard bradycardia indications for dual chamber pacemaker implantation. The incidence, predictors, and clinical consequences of atrial fibrillation (AF) developing after pacemaker implantation in the PASE trial were studied prospectively. During a median follow-up of 18 months, AF developed in 73 (18%) patients. Kaplan-Meier estimated cumulative incidences of AF in patients with sinus node dysfunction (n=176) at 18 months were 28% in the VVIR and 16% in the DDDR groups (P=0.08). After adjustment for other clinical variables using a Cox multivariate regression model, randomization to VVIR compared with DDDR pacing mode among patients with sinus node dysfunction was independently associated with a 2.6-fold increased relative risk (RR) of developing AF after pacemaker implantation (P=0.01). Other independent clinical risk factors for development of postimplant AF included a preimplant history of hypertension (P=0.02) or supraventricular tachyarrhythmias(P<0.04). Patients who developed AF had similar health related quality of life scores and cardiovascular functional status after 18 months of pacing as patients who remained free of AF. The RR of death, stroke, or heart failure hospitalization was not increased in patients who developed AF. Thus, in the elderly patients with sinus node dysfunction requiring permanent pacing, DDDR pacing mode protected against the development of AF. However, development of AF after pacemaker implantation in this population was not associated with a significant impact on quality-of-life, functional status, or other clinical endpoints during 18 months of follow-up.     

Atrial Fibrillatory Electrogram Measurement Allows Atrial Lead Placement in Patients Who Develop Atrial Fibrillation During Permanent Dual Chamber Pacemaker Implantation

The benefit of DDD(R) pacing is proven even in patients with intermittent atrial fibrillation. Atrial fibrillation developing during dual chamber pacemaker implantation creates a difficult problem. Maneuvers to reestablish a stable atrial rhythm often are required if atrial fibrillation sets in. This study was performed to determine if atrial lead placement can be performed with acceptable long-term results in the presence of atrial fibrillation. Twenty-one patients in whom atrial fibrillation developed during permanent pacemaker implantation were included in this study. In 12 patients, episodes of intermittent atrial fibrillation had been documented before the procedure. Screw-in leads were used in 15 patients and J-shaped passive fixation leads in 6 patients. AH leads were bipolar. The intraoperative atrial fibrillation electrogram amplitudes ranged from 0.9 to 3.2 mV (mean 1.8 ± 0.6 mV). One patient required lead revision due to a high atrial pacing threshold after conversion to SR. One patient remained in atrial fibrillation at 3-month follow-up. The other 20 patients converted to SR, 11 of whom had intermittent atrial fibrillation with successful mode switch activation. P wave amplitudes were 2.8 ± 6 mV (range 1.4 to 4.0 mV) after conversion to SR. The mean atrial pacing threshold was 1.1 ± 0.5 V (range 0.5 to 3.5 V). Placement of atrial leads in patients who develop atrial fibrillation during pacemaker implantation is feasible; fibrillatory electrogram amplitudes showed a good correlation with the atrial signal after conversion to an organized atrial rhythm (r = 0.698). Acceptable atrial pacing thresholds can be expected as well.     

Incidence and Predictive Factors of Atrial Fibrillation in Paced Patients

We have designed a prospective observational study to analyze the incidence and predictive factors of atrial fibrillation (AF) during a long follow-up, in a large population. Atrial fibrillation episodes were documented by the fallback mode switch (FMS) provided by implanted pacemakers. We have included 377 patients (61% men). The pacing indications were atrioventricular (AV) block (49%), sinus node disease (SND, 16%), bradycardia-tachycardia syndrome (BTS, 5%), AV block + SND (19%), AV block + BTS (6%), and BTS + SND (5%). The mean age at implant was 75 ± 12 (range 28–95). Atrial fibrillation before inclusion was documented in 10% of patients. Drug therapy at first follow-up included beta-adrenergic blockers (17% of the patients), amiodarone (13%), and others (16%). The mean follow-up was 30 ± 24 weeks. At least one AF episode was stored during follow-up in the memory of 169 pacemakers (45%). Among patients without history of AF at implant, 46% had documented FMS during follow-up. Patients with AF received more antiplatelet medications than patients without AF (P = 0.03). In patients with AF, New York Heart Association functional class was slightly higher, amiodarone and sotalol were more often prescribed, and the proportion of hypertension was higher than in patients without AF. However, these trends were not statistically significant. A significant higher incidence of premature atrial beats was observed in patients with AF than patients without AF (P < 0.0002). Patients with AF had a lower atrial percentage of paced events (55%) than patients without AF (63%, P < 0.02). These preliminary results confirm the high incidence of AF in paced patients and suggest a preventive effect of atrial pacing. The effects of other clinical variables may be confirmed with a longer follow-up in a larger population.     

Symptoms, Cardiovascular Risk Profile and Spontaneous ECG in Paced Patients: A Five-Year Follow-Up Study

GRIMM, W., ET AL.: Symptoms, Cardiovascular Risk Profile and Spontaneous ECG in Paced Patients: A Five-Year Follow-Up Study. Only few data are available about the course of symptoms, cardiac diseases, and spontaneous rhythm in pacemaker patients. Therefore, we followed the course of 308 paced patients (age 72 ± 11 years) with a mean implantation time of 63 ± 45 months. Results: The symptom triad of syncope, dizziness, and dyspnea improved remarkably in 93% of patients. Thirty-nine percent suffered from coronary heart disease. The risk factors of hypertension (47%), nicotine (37%), and diabetes mellitus (25%) were found significantly more often than in a normal population with the same age and sex profile. In VVI paced patients with sick sinus syndrome (SSS, n = 67) atrial fibrillation (AF) occurred significantly more often (42%) than in patients with AV block (n = 80, 23%, p < 0.05). Only one out of 41 DDD paced patients showed AF at follow-up. VVI stimulation seems to favor AF due to retrograde conduction in SSS. Only 3% of patients with SSS developed second- or third-degree AV block. Therefore, atrial pacing is preferable in most patients with SSS.     

Acute Atrial Endocardial P Wave Amplitude and Chronic Pacemaker Sensitivity Requirements: Relation to Patient Age and Presence of Sinus Node Disease

Data are reviewed from 88 patients who received double, passive-fixation unipolar endocardial leads for DDD pacemaker treatment. Identical electrodes were used in the right atrium and the right ventricle. Intra-atrial P wave amplitudes, intraventricular QRS complex amplitudes, and atrial and ventricular pacing thresholds were determined at implantation. The intra-atrial P wave amplitudes were not significantly correlated to the intraventricular QRS complex amplitudes. No significant correlation was found between the atrial stimulation thresholds and the ventricular pacing thresholds. The intra-atrial P wave amplitude showed a significant inverse and logarithmic correlation with patient age (P = 0.007). Furthermore, patients with sinus node disease had significantly lower intra-atrial P wave amplitudes (P = 0.04) than patients without this abnormality. The acute atrial and ventricular pacing thresholds and the intraventricular QRS complex amplitude were not correlated to patient age or presence of sinus node disease. Patients requiring higher atrial amplifier sensitivity settings during follow-up were significantly older (P less than 0.05) than those in whom lower atrial sensitivities were sufficient. A postoperative attenuation of the atrial electrogram was detectable by sensitivity programming procedures in 29 of the patients (35%). This phenomenon did not significantly relate to patient age or presence of sinus node disease. No case of permanent atrial undersensing occurred. It is suggested that the lower intra-atrial P wave amplitudes in older patients and patients with sinus node disease reflect degenerative changes in the atrial myocardium. The statistical relations found appear to motivate special attention to atrial sensing in these patient groups.     

P wave dispersion on 12-lead electrocardiography in patients with paroxysmal atrial fibrillation

The prolongation of intraatrial and interatrial conduction time and the inhomogeneous propagation of sinus impulses have been shown in patients with atrial fibrillation. Recently P wave dispersion (PWD), which is believed to reflect inhomogeneous atrial conduction, has been proposed as being useful for the prediction of paroxysmal atrial fibrillation (PAF). Ninety consecutive patients (46 men, 44 women; aged 55 +/- 13 years) with a history of idiopathic PAF and 70 healthy subjects (42 men, 28 women; mean age 53 +/- 14 years) were studied. The P wave duration was calculated in all 12 leads of the surface ECG. The difference between the maximum and minimum P wave duration was calculated and this difference was defined as P wave dispersion (PWD = Pmax-Pmin). All patients and controls were also evaluated by echocardiography to measure the left atrial diameter and left ventricular ejection fraction (LVEF). There was no difference between patients and controls in gender (P = 0.26), age (P = 0.12), LVEF (66 +/- 4% vs 67 +/- 5%, P = 0.8) and left atrial diameter (36 +/- 4 mm vs 34 +/- 6 mm, P = 0.13). P maximum duration was found to be significantly higher in patients with a history of PAF (116 +/- 17 ms) than controls (101 +/- 11 ms, P < 0.001). P wave dispersion was also significantly higher in patients than in controls (44 +/- 15 ms vs 27 +/- 10 ms, P < 0.001). There was a weak correlation between age and P wave dispersion (r = 0.27, P < 0.001). A P maximum value of 106 ms separated patients with PAF from control subjects with a sensitivity of 83%, a specificity of 72%, and a positive predictive accuracy of 79%. A P wave dispersion value of 36 ms separated patients from control subjects with a sensitivity of 77%, a specificity of 82%, and a positive predictive accuracy of 85%. In conclusion, P maximum duration and P wave dispersion calculated on a standard surface ECG are simple ECG markers that could be used to identify the patients with idiopathic paroxysmal atrial fibrillation.     

P Wave Recognition and Atrial Stimulation with Fractally Iridium Coated VDD Single Pass Leads

The bottleneck of VDD systems is the reliable detection of the small atrial signals by a floating atrial electrode. Fractally iridium coated electrodes offer excellent sensing and pacing performance. In this study, the performance of such a floating atrial lead in P wave sensing and synchronous ventricular stimulation was examined. Atrial pacing was also used as a test of atrial wall contact. Patients and Methods : A fractally iridium coated VDDlead was implanted in 18 patients. In 15 patients it was interfaced with a VDD pacemaker and in 3 patients with a DDD system depending on the P wave amplitude measured acutely (≥ 2 mV). Simultaneous recordings of the surface ECG and pacemaker telemetry were used to analyze P wave amplitudes and AV synchrony in different body positions, and during normal and deep breathing. Additionally, exercise tests based on daily life activities and 24-hour ECG monitoring were performed to test the pacemaker function. Results : During implantation P wave amplitudes were 1.86 mV ± 1.08 mV (range 0.5–4.9 mV) and during follow-up (6.6 ± 5.6 weeks) 0.18–3.8 mV. Holter recordings revealed reliable P wave sensing at a sensitivity setting of 0.5 mV (95.5%). P wave sensing was further improved by a higher atrial sensitivity. AV synchronous pacing ± 99.9% was achieved in all patients. In 7 patients the atrial electrode could be positioned close to the atrial wall enabling atrial stimulation thresholds at an average of 4.3 volts. Conclusion : This fractally iridium coated VVD lead allowed consistent and reliable P wave sensing at an atrial sensitivity as low as 0.5 mV in selected patients.     

Detection of Atrial Activation By Intraventricular Electrogram Morphology Analysis: A Study to Determine the Feasibility of P Wave Synchronous Pacing From a Standard Ventricular Lead

The detection of atrial activation from a standard ventricular pacing lead with standard ventricular electrodes would provide patients with VVI and VVIR pacing systems atrial rate response and atrial synchrony. In addition to potentially increasing cardiac output appropriately in these patients at rest and during moderate exercise, P wave sensing with such a device could help reduce pacemaker syndrome. In this study, unipolar signals from distal and proximal intraventricular electrodes were recorded from the right ventricular apex in 20 patients. Unipolar eJectrograms from 16 patients were recorded using temporary electrophysiology catheters and in four patients using permanent pacemaker leads. Approximately 3 minutes of data per patient were acquired and analyzed. After selection of a P wave template, the difference in baseline normalized area between the template and signal was calculated on a point-by-point basis. The percent of atrial depolarizations correctly detected was determined for each patient and lead configuration at the optimal threshold. Far-field P wave accuracy was better at the proximal electrode (74 ± 25%) than at the distal electrode (57 ± 34%) (P < 0.025). At the proximal electrode, 15/20 (75%) patients had > 70% accuracy and 11/20 (55%) patients had > 80% accuracy. At the distal electrode, 10/21 (48%) patients had > 70% accuracy and 7/21 (33%) patients had > 80% accuracy. In conclusion, far-field detection of atrial activation at the ventricular proximal electrode appears possible with sufficient accuracy to provide periods of atrial rate response and synchrony in patients with a single standard lead.     

Recording Atrial Monophasic Action Potentials Using Standard Pacemaker Leads:

AF leads to electrophysiological changes, but it is not known if similar alterations also appear before the onset of the first episode of AF because invasive electrophysiological studies are not justified in otherwise symptom-free patients. To address this question requires a safe method of obtaining atrial electrophysiological parameters at no extra risk or discomfort for the patient. The aim of this study was to test if recording of monophasic action potentials (MAPs) is feasible during pacemaker implantation. The study included 22 patients undergoing pacemaker implantation for symptomatic bradycardia without any history of AF. Using a custommade amplifier and a minor modification of the routine procedure for intraoperatively measured P waves, atrial electrograms could be recorded using a standard active pacemaker lead. MAP-like electrograms were obtained in 15 patients. MAP amplitude was 2.6 +/- 0.3 mV, mean action potential duration was 316 +/- 12 ms at a spontaneous heart rate of 67.2 +/- 3.2 beats/min. MAP duration was decreased when atria were stimulated at shorter cycle lengths (249 +/- 12 ms at 150 beats/min, P <0.05 vs sinus rhythm). In about two thirds of patients undergoing pacemaker implantation, recording of MAP-like electrograms was feasible with only minor modification of the atrial electrogram recording technique. The method should allow screening patients for electrophysiological alterations even before the onset of AF.