Atrial Electrodes Research Articles

Temporary Epicardial Atrial Pacing Electrodes: Duration of Effectiveness Based on Position

To investigate the duration of effectiveness in the postoperative period of temporary epicardial atrial pacing electrodes on the right atrium, based on position.The function of temporary epicardial atrial pacing electrodes were examined in 55 patients undergoing coronary artery bypass grafting from March 20, 1996, to July 31, 1996, at Allegheny University Hospitals, Hahnemann Division, Philadelphia, PA. There were 41 male and 14 female patients. The mean age was 71 years (range 35 to 86 years). Two atrial and two ventricular temporary epicardial pacing electrodes were placed at the termination of cardiopulmonary bypass. One atrial electrode was placed on the body of the right atrium at the junction of the superior vena cava (body electrode); the other was passed through the pursestring of the atrial cannulation site (appendage electrode).The mean thresholds for the atrial body electrodes on the operative day and postoperative days 1 and 2 were 4.96, 6.67, and 6.80 mA, respectively. The mean thresholds for the atrial appendage electrodes were 5.98, 7.50, and 8.59 mA, respectively.Temporary epicardial atrial pacing electrodes are more effective when the wires are placed in the atrial body of the right atrium than if they are wrapped within the pursestring of the right atrial appendage. As a result of these findings, the common practice of placing the pacing wire through pursestring tissue should be abandoned.

Temporary Atrial Electrode for the Treatment of Supraventricular Tachycardia After Cardiac Operations

Background. Supraventricular tachycardia is a common postoperative complication early after cardiac operations. A temporary atrial patch electrode for low-energy atrial defibrillation was developed in 1992 and subsequently tested.Methods. The electrode first was tested and removed intraoperatively during open heart operations in 10 patients (phase I). After the intraoperative testing, the temporary atrial patch electrode was implanted in 20 patients for postoperative termination of spontaneous episodes of supraventricular tachycardia (phase II). When supraventricular tachycardia occurred, biphasic shocks (1.2 to 5 J) were applied and the atrial defibrillation thresholds were measured.Results. In phase I, the mean intraoperative atrial defibrillation threshold was 1.6 ± 1.4 J, with a mean shock impedance of 64 ± 7.3 Ω. In phase II, 6 of 20 patients (30%) had 7 episodes of atrial fibrillation (n = 6) and atrial flutter (n = 1) after operation. In 5 patients, the supraventricular tachycardia could be converted to a sinus (n = 5) or normofrequent atrioventricular rhythm (n = 1). The mean postoperative defibrillation threshold was 2.7 ± 2.1 J, with a mean shock impedance of 50.2 ± 6.8 Ω.Conclusions. The temporary atrial patch electrode allows low-energy defibrillation of episodes of atrial fibrillation. It may serve as an alternative therapeutic option for the treatment of supraventricular tachycardia.

Limitation of Long-Term Atrial Pacing Via Floating Ring Electrode Using Overlapping Biphasic Impulse Stimulation in Ambulatory-Paced Patients

Long-term atrial pacing with overlapping biphasic impulse stimulation using floating atrial electrodes is limited in its use by the high rate of intermittent failure to capture the atrium and by the occurrence of diaphragmatic stimulation in ambulatory patients.

The Importance of the Left Atrioventricular Interval during Atrioventricular Sequential Pacing

During atrioventricular (AV) sequential pacing from the right heart, the interval between the left atrium and ventricle may vary from the programmed AV interval depending on the position of the atrial and ventricular electrodes and interatrial and interventricular conduction. The aim of this study was to determine the hemodynamic effects of altering the left AV interval while keeping the programmed AV interval constant. Four male and 17 female patients, aged 49 +/- 15 years were studied. The left AV interval was measured by a catheter in the coronary sinus. Stroke volume and mitral flow were measured by simultaneous echo Doppler during AV sequential pacing from the right atrial appendage and right ventricular apex at programmed AV intervals of 100, 60, and 6 ms. The atrial catheter was then positioned on the atrial septum and the measurements repeated. With the atrial catheter in the right atrial appendage, interatrial activation time (118 +/- 20 ms) was similar to interventricular activation time (125 +/- 21 ms) and the left AV interval was almost identical to the programmed right AV interval. There was a significant correlation between interatrial and interventricular activation times (r = 0.8; P < 0.001). Positioning the atrial electrode on the septum decreased interatrial activation time by 39 +/- 12 ms and increased the left AV interval by a similar amount. At a programmed AV interval of 60 ms, the left AV interval increased from 67 +/- 15 ms to 105 +/- 17 ms after the atrial catheter was repositioned from the appendage to the septum (P < 0.001). Compared to pacing from the right atrial appendage, atrial septal pacing increased mitral A wave velocity integral (2.8 +/- 1.4 vs 4.4 +/- 1.7 cm at a programmed AV interval of 60 ms, P < 0.01), decreased E wave velocity integral (8.1 +/- 2.2 vs 6.1 +/- 2.4 cm, P < 0.001) but did not alter stroke volume (44.8 +/- 10.6 vs 44.9 +/- 10.1 mL). In contrast, a 40 ms decrease in the programmed right AV interval from 100 to 60 ms decreased stroke volume from 48.0 +/- 10.0 to 44.9 +/- 10.2 mL (P < 0.001). There was a strong relationship between interatrial and interventricular conduction so that patients with prolonged interatrial conduction still had equivalent left and right AV intervals during atrioventricular sequential pacing from the right atrial appendage and right ventricular apex. Positioning the atrial electrode on the septum decreases interatrial activation time and increases the left AV interval by about 40 ms but has minimal hemodynamic effect in patients without heart failure.

Electrical remodeling due to atrial fibrillation in chronically instrumented conscious goats: roles of neurohumoral changes, ischemia, atrial stretch, and high rate of electrical activation.

Recently, we developed a goat model of chronic atrial fibrillation (AF). Due to AF, the atrial effective refractory period (AERP) shortened and its physiological rate adaptation inversed, whereas the rate and stability of AF increased. The goal of the present study was to evaluate the role of (1) the autonomic nervous system, (2) ischemia, (3) stretch, (4) atrial natriuretic factor (ANF), and (5) rapid atrial pacing in this process of electrical remodeling. Twenty-five goats were chronically instrumented with multiple epicardial atrial electrodes. Infusion of atropine (1.0 mg/kg; n=6) or propranolol (0.6 mg/kg; n=6) did not abolish the AF-induced shortening of AERP or interval (AFI). Blockade of K+(ATP) channels by glibenclamide (10 micromol/kg; n=6) slightly increased the AFI from 95+/-4 to 101+/-5 ms, but AFI remained considerably shorter than during acute AF (145 ms). Glibenclamide had no significant effect on AERP after electrical cardioversion of AF (69+/-14 versus 75+/-15 ms). Volume loading by 0.5 to 1.0 L of Hemaccel (n=12) did not shorten AERP. The median plasma level of ANF increased from 42 to 99 pg/mL after 1 to 4 weeks of AF (n=6), but ANF infusion (0.1 to 3.1 microg/min, n=4) did not shorten AERP. Rapid atrial pacing (24 to 48 hours; n=10) progressively shortened AERP from 134+/-10 to 105+/-6 ms and inversed its physiological rate adaptation. Electrical remodeling by AF is not mediated by changes in autonomic tone, ischemia, stretch, or ANF. The high rate of electrical activation itself provides the stimulus for the AF-induced changes in AERP.

Clinical Shock Tolerability and Effect of Different Right Atrial Electrode Locations on Efficacy of Low Energy Human Transvenous Atrial Defibrillation Using an Implantable Lead System

Objectives. The objectives of this study were 1) to evaluate the effect of different right atrial electrode locations on the efficacy of low energy transvenous defibrillation with an implantable lead system; and 2) to qualitate and quantify the discomfort from atrial defibrillation shocks delivered by a clinically relevant method.Background. Biatrial shocks result in the lowest thresholds for transvenous atrial defibrillation, but the optimal right atrial and coronary sinus electrode locations for defibrillation efficacy in humans have not been defined.Methods. Twenty-eight patients (17 men, 11 women) with chronic atrial fibrillation (AF) (lasting ≥1 month) were studied. Transvenous atrial defibrillation was performed by delivering R wave-synchronized biphasic shocks with incremental shock levels (from 180 to 400 V in steps of 40 V). Different electrode location combinations were used and tested randomly: the anterolateral, inferomedial right atrium or high right atrial appendage to the distal coronary sinus. Defibrillation thresholds were defined in duplicate by using the step-up protocol. Pain perception of shock delivery was assessed by using a purpose-designed questionnaire; sedation was given when the shock level was unacceptable (tolerability threshold).Results. Sinus rhythm was restored in 26 of 28 patients by using at least one of the right atrial electrode locations tested. The conversion rate with the anterolateral right atrial location (21 [81%] of 26) was higher than that with the inferomedial right atrial location (8 [50%] of 16, p < 0.05) but similar to that with the high right atrial appendage location (16 [89%] of 18, p > 0.05). The mean defibrillation thresholds for the high right atrial appendage, anterolateral right atrium and inferomedial right atrium were all significantly different with respect to energy (3.9 ± 1.8 J vs. 4.6 ± 1.8 J vs. 6.0 ± 1.7 J, respectively, p < 0.05) and voltage (317 ± 77 V vs. 348 ± 70 V vs. 396 ± 66 V, respectively, p < 0.05). Patients tolerated a mean of 3.4 ± 2 shocks with a tolerability threshold of 255 ± 60 V, 2.5 ± 1.3 J.Conclusions. Low energy transvenous defibrillation with an implantable defibrillation lead system is an effective treatment for AF. Most patients can tolerate two to three shocks, and, when the starting shock level (180 V) is close to the defibrillation threshold, they can tolerate on average a shock level of 260 V without sedation. Electrodes should be positioned in the distal coronary sinus and in the high right atrial appendage to achieve the lowest defibrillation threshold, although other locations may be suitable for certain patients.

Induction of Atrial Fibrillation With Low-Energy Defibrillator Shocks in Patients With Implantable Cardioverter Defibrillators

In a population of 151 consecutive patients who received an implantable cardioverter defibrillator, we found that atrial fibrillation was induced by low-energy shocks in 19% and was most common in patients with lead systems that included a right atrial electrode. Our finding that there was a fixed relation between the energy required to fibrillate (< or = 3 J) and defibrillate (> 3 J) suggests the presence of an upper limit of vulnerability in the human atrium.

Spontaneous Atrial Flutter in a Chronic Canine Model of the Modified Fontan Operation

Objectives. This study sought to 1) establish whether the atrial flutter (AFL) inducible acutely occurs spontaneously in a chronic canine model, and 2) characterize any reentrant circuits present chronically.Background. We previously demonstrated, in an acute canine model of the modified Fontan operation, that the lateral tunnel suture line creates a sufficient electrophysiologic substrate for AFL.Methods. Using cardiopulmonary bypass, a suture line was placed through a right atriotomy in adult dogs (n = 7) to simulate the lateral tunnel of the Fontan operation. Holter recordings were made preoperatively, on the first postoperative day and 2, 4 and 6 weeks postoperatively. At 6 to 8 weeks, through bilateral ventriculotomies, 253-point unipolar atrial electrodes were inserted. AFL was induced using atrial burst pacing, and endocardial activation sequence maps were created.Results. Preoperatively, all dogs were in sinus rhythm. Spontaneous AFL occurred in all dogs postoperatively, with a mean (±SD) cycle length of 192 ± 22 ms. At 6 weeks postoperatively, of six dogs that survived, four had intermittent AFL, and two had incessant AFL. At reoperation, sustained AFL was inducible in six of six dogs, with a mean cycle length of 194 ± 17 ms. Activation sequence maps demonstrated conduction block at the lateral tunnel suture line, which facilitated unidirectional conduction critical for propagation of the reentrant circuit. The AFL circuit was similar to that observed acutely.Conclusions. In a chronic canine model of the modified Fontan operation, the lateral tunnel suture line alone, in the absence of atrial stretch or hypertension, provides an electrophysiologic substrate that promotes spontaneous AFL. This model may be useful for evaluating various forms of treatment and prevention of AFL after the Fontan operation.

Toward optimizing a preshaped catheter and system parameters to achieve single lead DDD pacing.

P wave electrogram amplitudes and atrial stimulation thresholds were determined in eight Hanford miniature swine using a preshaped catheter with an "S" curve in the SVC, and a major lobe in the atrium to enhance electrode contact with the atrial wall. The catheter was designed for pacing and sensing in the DDD mode. P wave amplitudes were also ascertained with two commercially available VDD leads and compared to the data from the experimental catheters. The preshaped catheter used two 6-mm2 platinum iridium atrial electrodes with a 7-mm separation. Both atrial electrodes are on the same side of the catheter, facing outward on the major atrial lobe formed in the catheter. The P wave amplitudes were tested only in the differential bipolar configuration. For the eight preshaped catheters, the mean was 6.6 +/- 3.8 mV while for the conventional leads it was 2.9 +/- 1.6 mV. The mean atrial stimulation thresholds ranged from 1.1 +/- 0.2 V to 2.3 +/- 1.2 V, with still lower thresholds of 0.9-1.3 V when using the parallel unipolar atrial electrode configuration, in which both parts of the bipolar atrial electrode are configured as a unipolar electrode. The data suggest that bipolar simulation may be effective if sequential reverse polarity pulses are used to achieve cathodal stimulation from each electrode of the bipolar pair, on a beat-to-beat basis.

Clinical results with single lead VDD pacing.

For patients with atrioventricular block single lead atrial synchronous ventricular pacing (VDD) may have advantages compared to conventional dual chamber pacing (DDD) since it eliminates the need for an atrial lead. The purpose of this study was to investigate the clinical performance of a novel VDD pacemaker and the reliability of atrial sensing via the "floating' atrial electrode. 31 patients (10 females; age 64 +/- 13 years) underwent an implantation of a VDD pacemaker system (Intermedics UNITY). The patients were analyzed with regard to implantation parameters, complications and postoperative atrial sensing performance using the diagnostic data of the pacemaker memory. The mean follow-up was 6.3 (1-18) months. The implantation procedure did not differ from that of conventional single chamber pacemakers. Dislocation of a ventricular electrode was the only complication observed. The P wave at implantation was 1.6 +/- 0.9 mV and dropped to 0.9 +/- 0.4 mV at predischarge. During follow-up the atrial sensing threshold remained stable. The atrial sensing performance (percentage of atrial synchronous ventricular complexes) after reprogramming the highest atrial sensitivity was 99.7%. Two patients (6%) developed atrial fibrillation. 29 patients (94%) remained in VDD mode as primarily intended. From these results it is concluded that VDD pacing represents an excellent alternative in patients with atrioventricular block and intact sinus node function. The atrial sensing was found to be reliable.

Unipolar Pectoral Defibrillation Systems

Over the past 15 years, the implantation of automatic defibrillations has evolved from an obscure, impractical, and often morbid procedure to nearly a routine therapy. Initial large abdominally implanted generators with multiple epicardial leads have given way to much smaller, pectorally implanted systems utilizing only a single lead. These systems are better accepted by physicians and patients and rival recent-generation pacemakers in their implantation simplicity. Outcomes with single lead defibrillator implantation have been excellent. They are 99% effective at eliminating sudden death in large cohorts of patients, with overall survival of 94.4% at 18 months. Previously significant perioperative complications and mortality associated with epicardial systems have been virtually eliminated. Transvenous single lead systems now provide defibrillation efficacy at a level that makes epicardial leads unnecessary in most patients. Although inappropriate shocks are not a morbid complication, they still occur in approximately 15%-30% of patients. This is an area for improvement in defibrillator therapy, which, though invisible in total mortality statistics, is significant in terms of patient comfort and acceptance. Incremental improvements in pulse generator design and defibrillator lead technology are being made. Perhaps the most interesting new development will be the dual chamber device, incorporating and atrial electrode for sensing, pacing, and perhaps, atrial defibrillation. Such improvements will continue to make device therapy of all arrhythmias more versatile and improve patient comfort both in terms of device size and inappropriate shocks. It is unlikely, however, that further technological advances can further diminish the already small complication rate or improve the already excellent efficacy of current single lead systems. Defibrillator technology has already reached a maturity where technological improvements are less significant than efforts to better define the patient population who will benefit from the therapy.

Estimulação DDD com eletrodo único usando estimulação atrial bifásica simultânea: primeiros resultados clínicos

A estimulação de dupla câmara (DDD) com eletrodo único usando eletrodo atrial flutuante está limitada em função dos altos limiares encontrados para captura atrial. Avaliamos um sistema novo de cabo eletrodo para estimulação atrial que utiliza dois anéis atriais com pulsos de onda quadrada simultâneos unipolares lançados com polaridade oposta. O primeiro pulso é aplicado ao pólo distal do eletrodo e é positivo, o segundo pulso é aplicado ao pólo proximal do eletrodo e é negativo, ambos em relação à carcaça do gerador. O atraso entre os dois pulsos é programável entre 0,0 ms e 1,0 ms. A distância entre os anéis a nível atrial é de 10 mm e a distância entre o pólo distal atrial e o eletrodo ventricular unipolar pode ser selecionado entre 11, 13 e 15 cm. O posicionamento dos anéis a nível atrial é selecionado de acordo com a medida do limiar de estimulação do pulso bifásico simultâneo, incluindo manobras respiratórias para confirmar a captura/sense contínuos. O gerador de pulso tem uma única conexão para o eletrodo e a capacidade de aplicar os pulsos programáveis de onda quadrada com polaridades opostas, com atrasos programáveis de 0,0 a 1,0 ms. O gerador pode ser programado para estimulação VDD com eletrodo único. Este sistema foi implantado em 4 pacientes com bloqueio AV total e função sinusal normal. Os limiares de estimulação atrial e diafragmático foram medidos com várias configurações do pulso, larguras e atrasos, intra e pós-operatórios. A porção média do átrio direito foi selecionada como a melhor posição para os anéis atriais com captura contínua durante inspiração profunda. As medidas intra-operatórias e pós-operatórias (48 horas) foram: Limiar Intra-operatório Pós-operatório atrial unipolar 3,2 + 0,47 V não realizada atrial (bifásico simultâneo) 1,6 + 0,37 V 3,37 + 0,84 V diafragmático acima de 7 V 5,21 + 0,3 V sense de onda P 2,35 + 1,3 mV 1,27 + 0,8 mV Os pacientes tiveram alta com o gerador programado no modo VDD. A evolução de 30 dias após o implante mostrou perda de captura atrial transitória durante inspiração em 1 paciente, apesar da ausência de outras variações no limiar, comparado com a evolução de 48 horas pós implante. Em conclusão, a estimulação bifásica simultânea reduz o limiar de estimulação atrial, ao mesmo tempo em que mantém o sense atrial adequado com uma margem de segurança em relação à estimulação diafragmática.

Dual chamber pacing with a single lead system: initial clinical results.

A new mode of biphasic pacing was used in 26 patients to assess the feasibility of atrial pacing by means of the floating atrial ring electrodes of a single lead VDD permanent pacing system. During implantation, atrial pacing was possible in 25 patients with a 1-ms total pulse duration, a mean atrial threshold of 1.70 +/- 0.60 V (range, 0.6-3.0), and a mean diaphragmatic threshold of 6.7 +/- 2.5 V (range, 2.5-10.0). At 3 months, the atrial threshold had increased beyond 4.8 V in three patients. In the 22 other patients, the mean atrial threshold was 2.2 +/- 0.5 V (range, 1.50-3.50) in the supine position and 2.5 +/- 0.8 V (range, 1.5-4.8) in the sitting position. Stable atrial capture without diaphragmatic stimulation was achieved in 76% of patients.

Role of cardiac output in mediating arterial blood pressure oscillations.

The objective of this study was to determine the role of cardiac output in mediating spontaneous fluctuations in mean arterial pressure (MAP) conscious dogs. Dogs were chronically instrumented to monitor MAP and cardiac output. Atrioventricular (AV) block was induced, and left ventricular and right atrial electrodes were implanted. After recovery, MAP was observed for 5 min under two conditions: 1) normal variation in heart rate and cardiac output via triggering the ventricular stimulator with each atrial depolarization (effectively reversing the AV block, AV-linked stimulation) and 2) computer control of ventricular rate to maintain cardiac output constant on a by-beat basis at the same level as observed during normal variations in heart rate and cardiac output. When cardiac output was held constant, large-amplitude, low-frequency oscillations in MAP were readily apparent. Spectral analysis by fast Fourier transform revealed that during constant cardiac output the power observed at low frequencies in the MAP spectrum represented 95.0 +/- 2.7% of the total power compared with 75.5 +/- 4.6% during normal variations in heart rate and cardiac output (P < 0.05). In addition, when cardiac output was held constant, the power observed at higher frequencies markedly decreased from 24.5 +/- 4.6% of total power during AV-linked stimulation to only 5.0 +/- 2.7% of total power during constant cardiac output (P < 0.05). We conclude that low-frequency oscillations in MAP are due to changes in peripheral resistance, whereas a significant amount of high-frequency changes in MAP stems from spontaneous changes in cardiac output.

Pacemaker Upgrade for Recurrent Pacemaker Syndrome Using a Redundant Contralateral Electrode in a Patient with Bilateral Venous Stenoses

Following His-bundle ablation and VVIR pacemaker implantation, severe pacemaker syndrome developed and was treated with DDDR pacing, in a 70-year-old woman. Due to bilateral subclavian vein stenoses, DDDR pacing could not be maintained and an unusual method of restoring atrioventricular synchrony is described using the contralateral redundant atrial electrode connected to the ipsilateral dual chamber pacemaker and ventricular electrode.

Dependence of atrial sensing function on posture in a single-lead atrial triggered ventricular (VDD) pacemaker.

The influence of body posture on atrial sensing was examined in a single-lead VDD pacemaker in 16 patients. At implantation, a position was searched for the floating atrial bipolar sensor to obtain an adequate atrial signal amplitude. After 1-12 months the atrial signals were measured by programming the sensitivity in five postures: supine, sitting, and standing and lying on the right and left sides. The group mean amplitudes of the atrial signal were equal in all postures, and comparable to the supine value (1.01 +/- 0.51 mV). However, the values within each individual varied considerably according to position, by a range of 0.46 +/- 0.41 mV on average. Testing only supine did not always predict decent sensing when upright, e.g., in 3 patients the atrial signal decreased more than 0.5 mV. In 24-hour ambulatory electrocardiography, with the sensitivity (0.15-0.30 mV) set to cover all postures, atrial beats were undersensed not at all in 4 patients, < 0.01% in 6 patients, and < 0.1% in the remaining 6 patients. Thus, with a floating atrial electrode, sensitivity testing in various postures is advisable to ascertain proper sensing function.

Initial implant function and longevity of atrial pacing electrodes in children following cardiac surgery

Initial implant function and longevity of atrial pacing electrodes in children following cardiac surgery

Atrial activation during chronic atrial fibrillation in patients with isolated mitral valve disease

A computerized 32-channel mapping system has been developed to investigate the characteristics of the atrial activation sequence. The system is capable of displaying sequential atrial maps and provides a rapid and dynamic means of verifying the activation sequence of atrial fibrillation. Using this system, we performed intraoperative atrial activation mapping in 10 patients with chronic atrial fibrillation who were undergoing isolated mitral valve operations. Regular and repetitive activation (cycle length ranged from 131 to 228 milliseconds) originated in the left atrium in all 10 patients. Two patterns of repetitive activation in 2 patients and three patterns in 1 patient appeared alternately during the observation period in the left atrium. In contrast to the repetitive activation in the left atrium, the activation sequence of the right atrium was extremely complex and chaotic. In 7 of the 10 patients, the same pattern of right atrial activation was never repeated during the observation period. In 2 patients, revolution of repetitive activation in the right atrium sporadically appeared, but the pattern of activation immediately deteriorated to a complex and chaotic pattern. In 1 patient, repetitive activation emerged from the low lateral portion of the right atrium. Because our mapping technique was limited by the number of available atrial electrodes, discrete reentrant circuits or ectopic foci could not be demonstrated in the present study. However, the activation sequences during chronic atrial fibrillation suggested that (1) the left atrium would act as an electrical driving chamber for atrial fibrillation in the majority of the patients and (2) atrial activation patterns are different in each case. Computerized intraoperative mapping should guide surgeons in determining the appropriate surgical procedure and facilitate operation for chronic atrial fibrillation associated with mitral valve disease.

Premature atrial beat eliciting atrial fibrillation after coronary artery bypass grafting

Of patients undergoing coronary artery bypass grafting 30% develop atrial fibrillation (AF) or flutter. To determine if AF is initiated from the right or left atrium, atrial electrograms were continuously recorded in patients undergoing this procedure. In addition, to study whether the prematurity index of premature atrial contractions (PACs) eliciting AF differs from PACs not provoking AF, the distribution of prematurity indices was evaluated from R-R interval analysis. The right and left atrial recording electrodes were first activated by the ectopic beat provoking AF in six and eight patients, respectively. The prematurity index of the PAC eliciting AF was located in the middle (in half of the patients) or to the left of the median distribution of prematurity indices. The variability in activation of the atrial electrodes suggests that the PAC provoking AF can have its origin in the right, the septal, or the left region of the atrium. The initiation of AF depends on the prematurity index of the PAC.

Pseudo-Malposition of Permanent Pacemaker Electrodes Caused by Pneumothorax

A fifty-two-year-old man received a dual-chamber pacemaker with appropriate positioning of the leads via the right subclavian vein. About four days later he was noted to have developed a large right-sided pneumothorax. The roentgenogram showed displacement of the heart to the left and apparent displacement of the pacemaker leads with loss of the normal “J” configuration of the atrial electrode. On resolution of the pneumothorax, the electrode configurations returned to normal.