Pacemaker Features Research Articles

An approach towards individualized lower rate settings for pacemakers.

Author(s): Infeld, Margaret; Avram, Robert; Wahlberg, Kramer; Silverman, Daniel N; Habel, Nicole; Lustgarten, Daniel L; Pletcher, Mark J; Olgin, Jeffrey E; Marcus, Gregory M; Meyer, Markus

A Battery‐ and Leadless Heart‐Worn Pacemaker Strategy

AbstractOver the past half‐century, cardiac pacing technology has adhered to one basic system. However, many pacemaker‐related complications are related to this system, particularly in terms of the power supply and leads. Here, for the first time a heart‐worn pacemaker strategy is presented, which allows batteryless powering and leadless pacing. The batteryless feature is attained via heart‐extrusion energy scavenging through a micromachined piezoelectric thick film transducer. A record in vivo output current of 30 µA is obtained in an adult swine by the implanted piezoelectric transducer, which can effectively drive a commercial cardiac pacemaker. The exocardial pacing method is demonstrated by this batteryless pacemaker functions without a device or leads placed within the cardiac chambers. Lead‐ or batteryless options are being explored as new basic features of cardiac pacemakers. The presented heart‐worn pacemaker strategy may be useful in future pacing technology.

P6544A real world study of high frequency atrial anti-tachycardia pacing in new algorithm for atrial arrhythmia

Abstract Background Advanced pacemakers feature atrial antitachycardia pacing (aATP) therapies for terminating atrial arrhythmia. Previous studies showed the efficacy of combined atrial preventive pacing and aATP in patients with pacemakers. The independent effect of aATP and the impact for patients outside the clinical trials has not been well elucidated. Methods In a single center, prospective, all-comers trial, we enrolled 567 patients implanted cardiac devices with Reactive ATP function. History of permanent atrial fibrillation (AF) was not included. After device interrogation of the AF burden and the longest AF duration in the last 6 months, aATP was programmed as a bit more aggressive setting than MINERVA trial (time interval was set as every 2 hours). As for newly implanted devices, aATP was activated after at least 3 months run-in period. Primary and secondary outcomes were the longest AF duration and cumulative percentage of progression into permanent AF, respectively. Results Of 541 eligible patients, aged 75.3±10.7 years, 356 pacemaker, 82 ICD and 103 CRT patients, the longest single episode of AF lasted ≤6 min in 439 patients (81.1%), >6 min to 6 h in 43 (8.0%), >6–24 h in 33 (6.1%), and >24 h in 26 (4.8%) at the enrollment. During mean follow-up of 1.9 years, the longest AF episode lasted >24 h in 49 patients (9.1%) and 14 patients (2.6%) progressed into permanent AF. According with baseline longest single episode of AF, patients with AF ≤6 min developed an episode >24 h in 0.8% at 1 year and 3.2% at 2 years follow up; patients with AF >6 min to 6 h developed an episode >24 h in none at 1 year and 7% at 2 years follow up; and patients with AF >6–24 h developed an episode >24 h in 19% at 1 year and 42% at 2 years follow up, respectively. In a subgroup analysis of in 192 patients with at least 1 aATP, 46 patients with high efficacy (>44%) did not developed an episode >24 h. Only one patient developed into permanent AF without aATP therapy. On multivariate analysis, neither ICD nor CRT was independent risk factor for developing the longest AF episode >24 h. Conclusions The independent use of aATP without atrial preventive pacing was effective for preventing AF progression in a real world cohort. Even without the previous AF episodes, aATP could prevent AF development, especially in patients showing high aATP efficacy. Future research is required to enhance the aATP success rate.

Maintenance of ß-Cell Heterogeneity Is Required for Normal Islet Function

Aim: Recent studies have shown the existence of discrete β-cell subpopulations with differing levels of maturity and function. We sought here to understand how this diversity may influence islet function and insulin secretion using a ‘loss of heterogeneity‘ model. Material and Methods: Overexpression was achieved using an adenoviral polycistronic construct for Pdx1, MafA, Ngn3 and mCherry (Ad3-NPM). Pdx1 was silenced using short hairpin RNAs (shRNA). Gene and protein levels were detected by qPCR and immunohistochemistry (IHC), respectively. Ca2+ fluxes, ATP/ADP ratios and cAMP levels were analysed using dyes/biosensors and high-speed spinning disk microscopy. Glucose- (GSIS) and incretin-stimulated insulin secretion (ISIS) were measured using HTRF assays. Results: Ad3-NPM increased Pdx1 (12-fold vs. CT; P<0.01) and MafA levels (2-fold vs. CT) without affecting Ngn3. IHC showed that Pdx1 overexpression occurred predominantly in Pdx1low β-cells, forcing higher uniformity throughout the β-cell complement. The α/β-cell ratio did not change, indicating absence of transdifferentiation. Ca2+ responses to glucose were markedly blunted (ΔF=0.81 vs. 0.44 AU, CT vs. Ad3-NPM; P<0.01), and this was accompanied by a decrease in β-cell-β-cell cell connectivity and hub number (12.6 vs. 5.6 % hubs, CT vs. Ad3-NPM; P<0.05), the latter previously shown to be relatively immature cells with pacemaker features. ATP/ADP ratios and cAMP levels were unaffected. Glucose- and incretin-stimulated insulin secretion was impaired (% content secreted = 8.7 vs. 5.2 for GSIS and 56.4 vs. 29.02 for ISIS, CT vs. Ad3-NPM; both P<0.01). Similar results for Ca2+ dynamics, cellular connectivity and insulin secretion were obtained in islets treated with Pdx1 shRNA to increase the size of the Pdx1low population. Conclusion: Loss of β-cell heterogeneity, whether due to increased or decreased maturity, leads to islet failure and impaired insulin secretion. Thus, cellular diversity appears necessary for normal islet function. Disclosure D. Nasteska: None. G.A. Rutter: Research Support; Self; Servier. Q. Zhou: None. D. Hodson: None.

38Leadless cardiac dual-chamber pacing

Background: Recently introduced leadless cardiac pacemakers effectively overcome all lead-related limitations of conventional pacemaker systems. However, these devices only feature single-chamber pacing capability although dual-chamber pacing is highly desirable due to physiologic reasons. Implanting a leadless pacemaker into the right atrium and a second one into the right ventricle would enable leadless dual chamber pacing but requires wireless communication for device synchronization. Conventional radiofrequency telemetry is not suitable for this purpose due to its high energy consumption. Thus, an ultra-low power wireless communication method is crucial to preserve the pacemaker’s longevity (modern pacemakers consume only 5-10 µW of power). Purpose: Dual-chamber pacing capability for leadless pacemakers. Methods: Two pacemakers were developed that feature bidirectional wireless communication. Intra-body communication was implemented as communication method. This method uses the electrical conductivity of blood and tissue: the data from one device is modulated and applied as a small alternating current signal to the myocardial tissue and blood via electrodes. The signal is registered almost simultaneously by the other device. The communication frequency is ~100 kHz and therefore does not influence the heart’s functioning. The pacemakers feature an electrode pair for bipolar stimulation, the communication is performed over the same electrodes. The pacemakers were tested in an acute in-vivo trial on a 60 kg domestic pig. One pacemaker paced the right atrium, the other one the right ventricle. The atrial pacemaker served as master device and dictated the actual pacing rate, the atrioventricular (AV) pacing delay and pacing activity to the ventricular pacemaker in a wireless manner. Results: The pacemakers successfully performed dual-chamber pacing (D00) with wireless intra-body communication using the myocardium and blood as transmission path. No interference with the cardiac function was observed. The ECG sequence in Figure 1 shows the onset of leadless dual-chamber pacing recorded during the in-vivo trial: the atrial (A) and ventricular (V) pacing spikes are indicated by the arrows. The pacing rate was set to 120 bpm and the AV delay to 50 ms. Less than 1 µW average power was applied to the tissue for wireless communication. Conclusion: To our knowledge, this is the first report on successful leadless dual-chamber pacing during an in-vivo trial. Intra-body communication was integrated into a pacemaker system and has proven to be a promising, power-efficient wireless communication method for leadless dual-chamber pacemakers.

Variability in obstructive sleep apnea: Analysis of pacemaker-detected respiratory disturbances

Obstructive sleep apnea (OSA) is associated with several cardiovascular conditions. Some pacemakers feature specific algorithms detecting respiratory cycles and deriving indices well correlated with the identification of polysomnography-confirmed severe OSA. The purposes of this study were to analyze respiratory disturbances measured by a validated algorithm in clinical practice and to describe their variability over time and their association with atrial fibrillation. Fifty-eight patients implanted with dual-chamber LivaNova REPLY 200 DR or KORA 100 DR pacemakers measuring a respiratory disturbance index (RDI) were included. An RDI >20 events per hour of sleep is well correlated with severe OSA as determined by polysomnography. Patients with >10% nights with invalid RDI measurements were excluded. The RDI could be measured during 98% of nights. During a mean follow-up of 187 ± 123 days, the individual mean RDI was 19.9 ± 12.7 and was superior to 20 in 24 patients (41%). An RDI >20 events/h in at least 1 night was observed in 52 patients (90%). The mean day-to-day RDI variability in individual patients was 19% ± 21%. Patients with the highest burden of severe OSA (as defined by ≥75% of nights with RDI >20 events/h) were older, had a higher prevalence of hypertension, and were more often implanted for atrioventricular block than patients with lower burden of severe OSA. No RDI burden or cutoff was a predictor of atrial fibrillation occurrence. OSA is frequent in patients with a pacemaker and is reliably detected by pacemakers. OSA is highly variable and could probably be best analyzed in terms of burden.

Sudden shortening of the paced AV delay: is this normal pacemaker function?

The 200 ms paced AV delay is equal to the native AV conduction time, which leads to the phenomenon called ventricular pseudofusion as the ‘paced QRS’ morphology is identical to the native QRS morphology (QRS complexes marked with an asterisk, Fig. 1) [1]. This is an important observation for two reasons. First, the pacemaker should be reprogrammed to an extended paced AV delay to avoid unnecessary ventricular pacing. Secondly, the presence of ventricular pseudofusion is the clue to answer the question about the short paced AV delay of the third beat. Fig. 1 Postoperative standard 12-lead ECG (1 mV/10 mm, 25 mm/s paper speed). The pseudofusion QRS complexes are marked with an asterisk. See text for details There are various pacemaker features that can shorten the paced AV delay from the set parameter, e.g. ventricular safety pacing [2]. However, in this case, there is no need for knowledge about pacemaker features. If this was a normal pacemaker feature, we should see fully paced QRS morphology when the pacemaker shortens the AV delay to 110 ms (third beat on Fig. 1). The only potential physiological explanation is a junctional ectopy, occurring exactly on time with the ventricular pacing spike, exactly at the time the paced AV delay is shortened, which is extremely unlikely. Therefore, this has to be an artifact. When one examines the printed text above the ECG, the letters are squeezed together right above the part of the tracing with the shortened paced AV delay (rectangular frame in Fig. 1). The ECG machine intermittently stopped rolling the paper for about 90 ms at a time, effectively cutting out 90 ms segments from the ECG tracing. Since the paper had a pre-printed grid, this unusual artifact was not easily detectable.

MRI-conditional pacemakers: current perspectives

Use of both magnetic resonance imaging (MRI) and pacing devices has undergone remarkable growth in recent years, and it is estimated that the majority of patients with pacemakers will need an MRI during their lifetime. These investigations will generally be denied due to the potentially dangerous interactions between cardiac devices and the magnetic fields and radio frequency energy used in MRI. Despite the increasing reports of uneventful scanning in selected patients with conventional pacemakers under close surveillance, MRI is still contraindicated in those circumstances and cannot be considered a routine procedure. These limitations prompted a series of modifications in generator and lead engineering, designed to minimize interactions that could compromise device function and patient safety. The resulting MRI-conditional pacemakers were first introduced in 2008 and the clinical experience gathered so far supports their safety in the MRI environment if certain conditions are fulfilled. With this technology, new questions and controversies arise regarding patient selection, clinical impact, and cost-effectiveness. In this review, we discuss the potential risks of MRI in patients with electronic cardiac devices and present updated information regarding the features of MRI-conditional pacemakers and the clinical experience with currently available models. Finally, we provide some guidance on how to scan patients who have these devices and discuss future directions in the field.

Atrial antitachycardia pacing and managed ventricular pacing in bradycardia patients with paroxysmal or persistent atrial tachyarrhythmias: the MINERVA randomized multicentre international trial.

AimsAtrial fibrillation (AF) is a common comorbidity in bradycardia patients. Advanced pacemakers feature atrial preventive pacing and atrial antitachycardia pacing (DDDRP) and managed ventricular pacing (MVP), which minimizes unnecessary right ventricular pacing. We evaluated whether DDDRP and MVP might reduce mortality, morbidity, or progression to permanent AF when compared with standard dual-chamber pacing (Control DDDR).Methods and resultsIn a randomized, parallel, single-blind, multi-centre trial we enrolled 1300 patients with bradycardia and previous atrial tachyarrhythmias, in whom a DDDRP pacemaker had recently been implanted. History of permanent AF and third-degree atrioventricular block were exclusion criteria. After a 1-month run-in period, 1166 eligible patients, aged 74 ± 9 years, 50% females, were randomized to Control DDDR, DDDRP + MVP, or MVP. Analysis was intention-to-treat.The primary outcome, i.e. the 2-year incidence of a combined endpoint composed of death, cardiovascular hospitalizations, or permanent AF, occurred in 102/385 (26.5%) Control DDDR patients, in 76/383 (19.8%) DDDRP + MVP patients [hazard ratio (HR) = 0.74, 95% confidence interval 0.55–0.99, P = 0.04 vs. Control DDDR] and in 85/398 (21.4%) MVP patients (HR = 0.89, 95% confidence interval 0.77–1.03, P = 0.125 vs. Control DDDR). When compared with Control DDDR, DDDRP + MVP reduced the risk for AF longer than 1 day (HR = 0.66, 95% CI 0.52–0.85, P < 0.001), AF longer than 7 days (HR = 0.52, 95% CI 0.36–0.73, P < 0.001), and permanent AF (HR = 0.39, 95% CI 0.21–0.75, P = 0.004).ConclusionIn patients with bradycardia and atrial tachyarrhythmias, DDDRP + MVP is superior to standard dual-chamber pacing. The primary endpoint was significantly lowered through the reduction of the progression of atrial tachyarrhythmias to permanent AF.ClinicalTrials.gov IdentifierNCT00262119.

Detection of occult atrial fibrillation by pacemaker interrogation in cryptogenic stroke

Atrial fibrillation (AF) is a major cause of ischemic strokes, and it is assumed that occult intermittent episodes of AF are responsible for some of the seemingly cryptogenic strokes. Cardiac pacemakers feature rhythm diagnostic capabilities and data storage. We investigated whether pacemaker memory interrogation led to identification of undetected AF episodes prior to cryptogenic strokes. The study enrolled all patients admitted between June 2010 and July 2013 for an acute cryptogenic stroke and who were implanted with a permanent pacemaker. Patients with a history of AF and a history of stroke with an identifiable origin were excluded. Pacemaker memories were interrogated to determine the presence of AF prior to the stroke and its temporal relationship with the stroke. Fourteen patients (nine men and five women) with a median (interquartile range) age of 84.5 (82.25-87.5) years were included. Median CHADS2 and CHA2DS2-VASc scores were 2 (1-2.75) and 3.5 (3-4), respectively. Pacemaker memories were activated in 13 patients with atrial arrhythmia detection based on an atrial cutoff rate in 8 patients and on the detection of atrial rate acceleration in 5 patients. Electrograms were available for review in 10 patients. Unknown AF or atrial flutter was diagnosed previous to the stroke in six (43 %) patients. Four patients experienced more than one arrhythmia episode. The last episode occurred in the 48 h prior to stroke in three patients and in the previous 4 weeks in five patients. Anticoagulation was started after the stroke in all of these six patients. Pacemaker interrogation has a high diagnostic yield in seemingly cryptogenic stroke, with frequent detection of occult AF. The causal link between AF and stroke is convincingly reinforced by their close temporal proximity, and anticoagulation is warranted in this clinical situation.

Reflections of Hunger and Satiation in the Structure of Temporal Organization of Slow Electrical and Spike Activities of Fundal and Antral Stomach Muscles in Rabbits

Manifestations of hunger and satiation in myoelectric activity patterns in different portions of the stomach were studied in chronic experiments. The state of hunger manifested in the structure of temporal organization of slow electric activity of muscles in the stomach body and antrum in the form of bimodal distributions of slow electric wave periods, while satiation as unimodal distribution. In hunger-specific bimodal distribution of slow electric wave periods generated by muscles of the stomach body and antrum, the position of the first maximum carries the information about oncoming food reinforcement, since this particular range of slow wave fluctuations determines temporal parameters of slow electric activity of muscles in all stomach regions in the course of subsequent successive food-procuring behavior. Under conditions of hunger, the pacemaker features of muscles in the lesser curvature are realized incompletely. Complete realization is achieved in the course of food intake and at the state of satiation.

Body Sensors Applied in Pacemakers: A Survey

This paper presents a survey of the body sensors applied in pacemakers and recent advances in modern pacemaker systems. New features of modern pacemakers that are commercially available are briefly described. Body sensors incorporated in pacemakers are illustrated with their rationales, sensing signals, advantages, limitations and applications. Their further improvements are needed to better serve patients.

Pacing technology: advances in pacing threshold management

Over the last five decades, pacemaker therapy has undergone remarkable technological advances with increasing sophistication of pacemaker features. However, device longevity has remained one of the major issues in pacemaker design ever since the first endocardial pacing lead implantation in 1958. In addition to various hardware design to enhance device longevity, software-based solutions to minimize pacing energy and yet with good safety margin have also been developed. Together with desire and need of fully automatic pacing system in increasingly busy pacemaker clinic, several manufacturers have introduced different automatic threshold management algorithm. This article summarizes the current state-of-the-art management in pacing threshold in the modern pacemakers.

Pacing Technology: Advances in Threshold Management

Over the last 5 decades, pacemaker therapy has undergone remarkable technological advances with increasing sophistication of pacemaker features. However, device longevity has remained one of the major issues in pacemaker design ever since the first endocardial pacing lead implantation in 1958. In addition to various hardware design to enhance device longevity, software-based solutions to minimize pacing energy and yet with good safety margin have also been developed. Together with desire and need of fully automatic pacing system in increasingly busy pacemaker clinic, several manufacturers have introduced different automatic threshold management algorithm. This article summarizes the current state of art in pacing threshold management in the modern pacemakers.

Modern Pacemakers: Hope or Hype?

In recent years, the role of implantable pacing devices has expanded beyond the arrhythmia horizon and contemporary pacemakers' attempt to meet the physiological needs of patients. Modern pacemakers' functions include various modes of dual-chamber pacing, rate-response algorithms with dual sensors for optimum physiological response, cardiac resynchronization therapy (CRT), arrhythmia-prevention algorithms, antitachycardia pacing, and hemodynamic monitoring. The automaticity features of pacemakers enable continuous or intermittent monitoring of various pacemaker parameters including battery voltage, pacing impedance, sensing levels, pacing thresholds, and daily activity log. Modern pacemakers offer "physiological pacing" algorithms that minimize ventricular pacing and reduce the incidence of atrial fibrillation significantly. Ventricular pacing in patients with intact atrioventricular (AV) conduction or intermittent advanced AV block should be minimized with a hope to reduce heart failure hospitalization and mortality. A reduction in all-cause mortality due to physiological pacing, except for the CRT, has yet to be demonstrated in a randomized trial. Overall, modern pacemakers have acceptable performances to fulfill the clinical needs and have a reasonable safety margin. Promising new technologies are currently under development and offer hope to patients who may one day derive both symptomatic and mortality benefit from these devices.

YIA Abstracts: Best abstracts on clinical studies

YIA Abstracts: Best abstracts on clinical studies

Heart Rhythm Society Policy Statement Update: Recommendations on the Role of Industry Employed Allied Professionals (IEAPs)

R ntroduction n 2001, the North American Society of Pacing and Elecrophysiology (Heart Rhythm Society) published a policy tatement to provide guidance for industry employed allied rofessionals (IEAPs) who render technical assistance durng pacemaker/Implantable Cardioverter Defibrillator (ICD) mplantations, programming, analysis of malfunctions, and ollow-up. These principles were incorporated in a recent onsensus document on the monitoring of implanted cariovascular electronic devices. The term IEAP is applied o persons who are employed or contracted manufacturer epresentatives, field clinical engineers, and industry emloyed technical specialists. These individuals often have xpertise about specific features of pacemakers or ICDs that s unique to the manufacturer’s product. This expertise may e extremely valuable to physicians and the clinical allied rofessionals (CAPs) they employ. In some instances, CAPs ay be employed by the institution incident to the practice f the responsible physician. The physician bears the reponsibility for assessing effectiveness of device programing and any device malfunctions and recommending speific courses of action. The Heart Rhythm Society sponsored an Industry Forum n July 2007 to discuss the role of industry in the care of atients with heart rhythm disorders. One topic of discusion was the role of IEAPs and the need to update the uidelines published in 2001. The meeting was attended by enior Heart Rhythm Society (HRS) staff, officers of HRS, nd executives representing several leading manufacturers f technology used in the care of heart rhythm disorders. broader scope of devices is in widespread use today. lthough pacemakers and ICDs remain central to this disussion, the guidelines must also account for technical asistance supporting intra-cardiac echocardiography, electronatomic mapping systems, remote navigation, and other echnologies that are evolving to assist complex procedures

Minimizing Ventricular Pacing to Reduce Atrial Fibrillation in Sinus-Node Disease

Conventional dual-chamber pacing maintains atrioventricular synchrony but results in high percentages of ventricular pacing, which causes ventricular desynchronization and has been linked to an increased risk of atrial fibrillation in patients with sinus-node disease. We randomly assigned 1065 patients with sinus-node disease, intact atrioventricular conduction, and a normal QRS interval to receive conventional dual-chamber pacing (535 patients) or dual-chamber minimal ventricular pacing with the use of new pacemaker features designed to promote atrioventricular conduction, preserve ventricular conduction, and prevent ventricular desynchronization (530 patients). The primary end point was time to persistent atrial fibrillation. The mean (+/-SD) follow-up period was 1.7+/-1.0 years when the trial was stopped because it had met the primary end point. The median percentage of ventricular beats that were paced was lower in dual-chamber minimal ventricular pacing than in conventional dual-chamber pacing (9.1% vs. 99.0%, P<0.001), whereas the percentage of atrial beats that were paced was similar in the two groups (71.4% vs. 70.4%, P=0.96). Persistent atrial fibrillation developed in 110 patients, 68 (12.7%) in the group assigned to conventional dual-chamber pacing and 42 (7.9%) in the group assigned to dual-chamber minimal ventricular pacing. The hazard ratio for development of persistent atrial fibrillation in patients with dual-chamber minimal ventricular pacing as compared with those with conventional dual-chamber pacing was 0.60 (95% confidence interval, 0.41 to 0.88; P=0.009), indicating a 40% reduction in relative risk. The absolute reduction in risk was 4.8%. The mortality rate was similar in the two groups (4.9% in the group receiving dual-chamber minimal ventricular pacing vs. 5.4% in the group receiving conventional dual-chamber pacing, P=0.54). Dual-chamber minimal ventricular pacing, as compared with conventional dual-chamber pacing, prevents ventricular desynchronization and moderately reduces the risk of persistent atrial fibrillation in patients with sinus-node disease. (ClinicalTrials.gov number, NCT00284830 [ClinicalTrials.gov].).

Ventricular Pacing Threshold Variations in the Young

Ventricular Capture Management (VCM) is a Medtronic Kappa pacemakers (PM) feature that automatically measures pacing threshold through detection of the evoked response after a pacing stimulus. The aim of this study was to evaluate the range of variation of ventricular pacing threshold in pediatric patients with endocardial and epicardial pacing leads. Thirty-one patients (median age 6.5 years) were implanted with a Kappa 901 PM for atrioventricular block or sinus node dysfunction. Congenital heart defects (CHD) were present in 58% of patients. Ventricular leads were epicardial in 52% of patients. VCM was programmed to automatically measure threshold every 2 hours. In a median follow-up of 12 months, 27,110 threshold measurements, 72% of which were successful, have been taken in 94% of patients. Measurement success was 99% in the endocardial leads group (age at implantation 12 +/- 6 years) and 31% in epicardial leads (age 4 +/- 5 years) (P < 0.05). Main reasons for unsuccessful measurements were high heart rate and, in a patient with an endocardial lead, competition with intrinsic rhythm. Undersensing or oversensing of the evoked responses was not detected. In all successful VCM measurements, epicardial pacing and CHD contributed to stability of thresholds (multivariate analysis). Pacing threshold showed specific circadian patterns: higher thresholds were found between 00.00 and 06.00 a.m., but the variation was low, 0.03 +/- 0.01 V. In conclusion, children and young patients show stable ventricular thresholds, especially in presence of CHD, and epicardial leads are at least as stable as endocardial leads. Ventricular pacing threshold showed a circadian variability similar to that described in adults, that does not seem to influence VCM functioning and PM programming.

New Insights Into the Initiation of Atrial Fibrillation

This study investigated onset scenarios of atrial fibrillation (AF), the first phase of the Atrial Fibrillation Therapy (AFT) trial, to determine potential arrhythmogenic triggers as targets for atrial pacing algorithms that have been proposed for prevention of AF. Ninety-eight patients (58 men; age 65+/-11 years) with recurrent, symptomatic, drug-refractory AF and a conventional pacemaker indication in 31 of 98 received a dual-chamber pacemaker. Using novel diagnostic pacemaker features AF onset scenarios were prospectively evaluated in 612 AF episodes during a 2-month monitoring period, with atrial pacing limited to 40 bpm. The most common onset scenario was premature atrial complexes (PACs) before AF (48% onsets per patient), followed by bradycardia (33%), sudden onset (17%), and tachycardia (0%). Combinations of onset scenarios were frequent (median 2 different scenarios per patient). A main study finding was the significance of repetitive AF, with 33% of onsets per patient being initiated within 5 minutes of a previous AF episode. Sudden onsets were more frequent among patients with than without repetitive AF (24% versus 0% onsets per patient, P=0.011), whereas the proportion of PACs before AF was not statistically different (50% versus 37%, P=0.52); however, patients with repetitive AF had more PACs per hour (72 versus 29, P=0.023) and a higher number of AF episodes per day (17 versus 0, P=0.001) and were more likely to have at least 1 PAC-related onset (90% versus 53%, P<0.0001). Novel diagnostic pacemaker features allowed a detailed individual analysis of rate and rhythm changes before AF and thus uncovered a substantial intraindividual and interindividual variability of AF onset scenarios.