AV Conduction Research Articles

Reduction of Right Ventricular Pacing in Patients with Sinus Node Dysfunction Using an Enhanced Search AV Algorithm

Dual chamber pacing typically results in a high percentage of ventricular pacing. A number of studies have been conducted suggesting detrimental effects of ventricular desynchronization produced by long-term RV pacing. Pacemaker algorithms that extend the AV interval to uncover intrinsic AV conduction have been utilized to reduce ventricular pacing. These algorithms are often limited to AV intervals below 250 ms limiting the ventricular pacing reduction. We hypothesized that by allowing AV intervals to extend beyond 300 ms, a marked reduction in RV pacing can be achieved. A total of 30 patients (17 men, mean age 71 +/- 9) with standard Brady indications, and implanted with a Medtronic Kappa 700 pacemaker, were randomized to 2-week treatments with default Search AV (KSAV) parameters or Enhanced Search AV (ESAV) parameters. The Enhanced Search AV algorithm included the capability for continuous adjustment of AV delays and the ability to auto disable in patients with persistent AV block. Among patients with intact AV conduction, percent VP was greater in KSAV versus ESAV (70 +/- 40% vs 19 +/- 28%, P < 0.001). In patients with persistent AV block, the algorithm suspended appropriately and there was no significant change in the percent VP between both arms of the study. In 18/22 patients, percent VP was reduced below 40%. Substantial reduction in ventricular pacing can be achieved by allowing the AV interval parameters to extend beyond 300 ms using the ESAV algorithm. In patients with AV block, ESAV suspended and patients were paced at their nominal settings.

25 Determining optimal dual chamber algorithm to favor spontaneous AV conduction: preliminary results of the Saver study

25 Determining optimal dual chamber algorithm to favor spontaneous AV conduction: preliminary results of the Saver study

Outcome of pacing in different indications

Outcome of pacing in different indications

678 The incidence of ventricular pacing in patients with sinus node dysfunction and preserved AV conduction can be reduced using long AV delays and the DDIR mode

678 The incidence of ventricular pacing in patients with sinus node dysfunction and preserved AV conduction can be reduced using long AV delays and the DDIR mode

678 The incidence of ventricular pacing in patients with sinus node dysfunction and preserved AV conduction can be reduced using long AV delays and the DDIR mode

678 The incidence of ventricular pacing in patients with sinus node dysfunction and preserved AV conduction can be reduced using long AV delays and the DDIR mode

25 Determining optimal dual chamber algorithm to favor spontaneous AV conduction: preliminary results of the Saver study

25 Determining optimal dual chamber algorithm to favor spontaneous AV conduction: preliminary results of the Saver study

Calmodulin kinase II activity is required for normal atrioventricular nodal conduction

Multifunctional Ca2+/calmodulin-dependent protein kinase II (CaMKII) is abundant in myocardium. CaMKII activity is augmented by catecholamine stimulation, which enhances AV nodal conduction, suggesting the hypothesis that CaMKII also contributes to AV nodal conduction properties. The purpose of this study was to test the potential role of CaMKII in regulating AV nodal conduction in heart. We developed a novel mouse with genetic CaMKII inhibition by cardiac-specific expression of autocamtide 3 inhibitory peptide (AC3-I) mimicking a conserved sequence of the CaMKII regulatory domain. We also engineered a control transgenic mouse with cardiac expression of an inactive, scrambled version of AC3-I (autocamtide 3 control peptide [AC3-C]) and performed electrophysiologic measurements in vivo and in Langendorff-perfused isolated hearts. AC3-I and AC3-C were abundantly expressed in AV nodal cells. AC3-I mice with implanted ECG telemeters showed enhanced Wenckebach-type AV conduction block after isoproterenol (present in 9/9 mice) compared with AC3-C mice (present in 1/5 mice, P = .005). Intracardiac recordings showed significant PR and AH interval prolongation in AC3-I mice at baseline and after isoproterenol compared with AC3-C mice. HV durations were not different. Langendorff-perfused AC3-I hearts had significantly prolonged Wenckebach cycle lengths and AV nodal effective refractory periods compared with AC3-C hearts, whereas sinus node recovery time and left ventricular effective refractory times were similar between these genotypes. These studies define CaMKII as a critical determinant of normal and catecholamine-stimulated AV nodal conduction responses.

Reduction of unnecessary right ventricular pacing due to the managed ventricular pacing (MVP) mode in patients with symptomatic bradycardia: Benefit for both sinus node disease and AV block indications

Clinical evidence suggests that frequent, unnecessary right ventricular apical pacing may have adverse long-term effects including an increased risk of developing atrial fibrillation or congestive heart failure. Many patients who receive a pacemaker for SND have intact AV conduction. Some patients who receive a pacemaker for AVB have intermittent intact AV conduction. A managed ventricular pacing (MVP) mode which switches between AAI/R and DDD/R has been developed to reduce unnecessary right ventricular pacing (RVP). This feature was tested in the EnRhythm clinical study, a multicentre randomized single-blind crossover evaluation, conducted in 13 European and 5 Canadian centres. Subjects (n=149) receiving an EnRhythm Model P1501 DR pacemaker were randomized to MVP or DDD/R pacing mode for 1 month and crossed over to the alternate mode for a second month. An initial cohort of 65 patients, aged 71.8 ± 9.8 years and predominantly male (70.8%), had complete crossover data. Primary pacemaker indication was AVB in 29 (44.6%) patients and SND in 36 (55.4%) patients. Intact AV conduction was present at device implant in 41 (63.1%) patients. The MVP mode was associated with a median of 58.7% (p < 0.001) absolute reduction in percent RVP compared to the DDDR mode. The effect was observed in both patients with AVB or sinus node disease as the primary indication for pacing. Tabled 1

Circumferential reentrant pulmonary vein tachycardia - an unusual cause of left atrial “flutter”

A 46 year old man presented with recurrent symptomatic persistent atrial tachycardia (AT) four months after circumferential periostial pulmonary vein (PV) isolation for atrial fibrillation (AF). An out-patient ECG during tachycardiaand and on the day of ablation showed atrial tachycardia with cycle length of 273 ms and 2:1 AV conduction block. At electrophysiology study no diastolic or pre-systolic activation could be found in the RA, so a 15mm circumferential decapolar catheter was placed in the right superior (RS) PV via a transseptally placed sheath. This showed macroreentry in the RSPV with a cycle length of 144 ms that was completely mapped as a circumferential reentrant circuit with 2:1 conduction to the LA (Figure). The exit point to the LA demonstrated fusion of PV potentials to LA potentials (small arrows on figure) at PV 3–4. A single application of RF energy at PV 3–4 ablated the RSPV to LA connection with restoration of sinus rhythm in the LA and RA, without disrupting RSPV tachycardia. A single further application of RF energy at PV DS/PX then terminated the RSPV tachycardia. This is the first report of a persistent circumferential reentrant PV tachycardia with a 2:1 exit block simulating left atrial tachycardia (LAT). That the entire circuit was mapped by the circumferential catheter, with termination of tachycardia by a single application of RF energy at an area of fractionation within the circuit, provides good evidence that this was a reentrant tachycardia. PV reentry should be considered as one of the causes of AF or AT after a PV isolation procedure.

Commentary on the abstracts for Cardiostim 2005 Pacing and Haemodynamics: Art of Timing Budapest, Hungary, April 6–8, 2005

The Cardiostim team and Prof. Aladar Ronaszeki organised an educational meeting in Budapest from April 6 to 8 entitled “Pacing and Haemodynamics: Art of Timing”. This European congress has been an opportunity to discuss the haemodynamic effects of the various modes of pacing available, and more specifically Cardiac Resynchronisation Therapy (CRT) for heart failure patients. The reader will find below the 101 abstracts selected among the 156 received, printed in three different sections: conventional pacing, CRT, and a small set of abstracts on ablation techniques, which will not receive comment. Many investigations have demonstrated the deleterious effects of right ventricular (RV) apical pacing. Padeletti et al. (for the WHERE study) elegantly show the benefit of preserving spontaneous AV conduction in comparison with RV apical pacing, in DDD paced patients, via PEA measurements. PEA, which has been demonstrated to be closely correlated with LV d P /d t , significantly increases when patients are not RV paced, and decreases when they are RV paced. PEA variations parallel clinical outcomes and echo parameter values. When pacing is necessary, there is still controversy about the optimal RV pacing site. Direct His bundle pacing is feasible and safe (Catanzariti et al.), but requires normal function of the bundle branches and Purkinje system. Implantation is also difficult to perform. Long term reliability of His pacing is unknown. For Kutarski et al., RV outflow tract (RVOT) pacing is preferable to RV apical pacing. But for van Gelder, RV apical pacing is preferred for CRT patients. In our experience, RVOT and RV apical pacing provide similar haemodynamic results on average, but may induce significant individual differences. To help to understand individual requirements, one of the main targets for manufacturers is to propose haemodynamic sensors that could evaluate and guide the benefits of various pacing sites, such as …

CRAVT: A Prospective, Randomized Study Comparing Transvenous Cryothermal and Radiofrequency Ablation in Atrioventricular Nodal Re-entrant Tachycardia

Background Transvenous catheter ablation of atrioventricular nodal re-entrant tachycardia (AVNRT) with radiofrequency (RF) is effective and safe, but carries a 1–3% incidence of early and potentially late heart block. Cryothermy can create transient effects, and identify potentially successful ablation sites and decrease the risk for permanent heart block. Methods In this prospective, randomized trial 102 patients with recurrent narrow QRS-complex tachycardia suggestive of AVNRT were randomized to either RF or cryoablation before a diagnostic study. Results In 63 patients with AVNRT, 33 were randomized to RF and 30 to cryoablation. Procedural success was achieved, respectively, in 30 (91%) patients in the RF and 28 (93%) in the cryoablation group. The median number of cryothermal applications was significantly lower than the number of RF applications (2 versus 7, p <0.005). No accelerated junctional rhythm was seen with cryothermy, while it was present in 31/33 RF patients. Both fluoroscopy and procedural times were comparable. The radiological position of the successful site in relation to anatomical landmarks was slightly different ( p <0.05). No cryothermy related complications were observed, and no permanent AV conduction disturbances occurred. During a mean follow up of 13±7 months long-term clinical success was seen in one additional patient in each group. In the same period, 3 patients in both groups experienced recurrent AVNRT. Conclusion Cryoablation is as effective and safe as RF for AVNRT. Significantly fewer applications are necessary, with comparable procedure times. This makes cryothermy useful for the treatment of tachyarrhythmias near the compact AV node.

Mmyocardial performance evaluation after rv apical pacing: the “where” study

BACKGROUND RV apical pacing has been shown to decrease LV performance, which can be assessed either by Echo or by a pacing system equipped with a microaccelerometer (Sorin Biomedica, Italy) able to measure Peak Endocardial Acceleration, PEA, and therefore to evaluate LVdP/dtmax. AIM This multicentre (26 European Centres), prospective, randomised, crossover, single-blind study compares, intra-patient, LV function in 2 different settings of DDDR programmation: maintained spontaneous AV conduction or RV pacing at Optimized AV Delay (OAVD). METHODS 103pts (67M, 73.1±9.1yrs) were implanted with a Sorin BEST-Living System for SSS, sinus bradycardia, with QRS<120ms, PR<220ms.After 1 month (baseline) pacemakers were randomly programmed for 2 successive periods of 6 months either pacing interval with OAVD or in spontaneous AV conduction. Group1 began with 6mos pacing; group2 with 6mos of spontaneous conduction. Echo and PEA assessments and Quality of Life (QOL) evaluation were performed (in spontaneous AV conditions) at baseline, crossover and at the end of the 2nd period. RESULTS 87pts completed the study with similar baseline values. LVEDD:47.8±5.4 (Group1-41pts) and 47.9±5.8 (Group2-46pts); PEA:0.93±0.5 (Group1) and 0.96±0.52 (Group2) (p=ns). Both in Group1 and Group2 LVEDD increased during pacing period (from 47.8±5.4 to 50.4±5.5 and from 44.9±5.7 to 47.7±6.5 respectively; p<0.05) and decrease during spontaneous conduction (from 50.4±5.5 to 46.4±5.8 and from 47.9±5.8 to 44.9±5.7 respectively; p<0.05). PEA values for both Group1 and Group 2 decreased during pacing period (from 0.93±0.5 to 0.73±0.5 and from 1.20±0.64 to 0.95±0.54 respectively; p<0.05) and increased during spontaneous conduction (from 0.73±0.5 to 1.10±0.56 and from 0.96±0.52 to 1.20±0.64 respectively; p<0.05). CONCLUSIONS 1)Echo/PEA data confirm that RV apical decreases LV performance (contractility) 2)QOL improves during spontaneous AV conduction. 3)PEA may be employed to monitor LV function evolution in paced patients, saving costs and time of Echo

Determining optimal dual-chamber algorithm to favor spontaneous AV conduction: Preliminary results of the save R study

Determining optimal dual-chamber algorithm to favor spontaneous AV conduction: Preliminary results of the save R study

Preliminary results of the save r study: which is the best dual-chamber pacing mode to favor spontaneous av conduction ?

Different dual-chamber pacing modes are available to pace Sinus Node Dysfunction (SND) patients (pts). Inappropriate ventricular pacing has been associated with clinical complications such as heart failure and atrial fibrillation (AF). SAVE R study aims to assess the respective efficacy of different pacing modes, regarding preservation of spontaneous atrio-ventricular (AV) conduction. Methods The AAIsafeR mode behaves like an AAI mode until a predefined pattern of atrioventricular block (AVB) or ventricular pause occurs and triggers a temporary switch to DDD. This mode was evaluated in a prospective randomized parallel study with 2 other pacing modes: DDD/AMC and DDD with long AV delay (250 ms). Pts with no documented persistent AVB, a PR interval<250 ms and Atrial Fibrillation (AF) duration<30% of follow-up (FU) duration were randomized after 1 month of FU in one of the 3 arms (1:1:1). Visits were planned at 3 months and 1 year after implantation. The main objective was the ventricular pacing ratio at 3 months FU, as retrieved from pacemaker statistics. Results One-hundred and one pts implanted with a Symphony DR / D pacemaker (ELA Medical, France) were randomized (59% males, 73±10 years). Indications were SND (40%), Brady-Tachy syndrome (28%), paroxysmal AVB (32%). Up to 60/101 randomized patients were controlled at 3 months. No adverse event or symptom related to the pacing system was reported during FU. [Table 1][1] displays the mean percentage of A and V pacing observed in each arm: View this table: Conclusion Conclusion. AAIsafeR appears to be the most efficient pacing mode to prevent ventricular pacing. A longer FU is necessary to analyze the effect of each mode on AF incidence. [1]: #T1

Right ventricular bifocal DDD pacing as primary choice for cardiac resynchronization in heart failure patients with severe mitral regurgitation

Right ventricular bifocal DDD pacing (RVBP), performed at apex and at the root of interventricular septum (RIVS), reduces duration of paced QRS (QRSD) and mitral regurgitation (MR). Our study is addressed to assess if chronic RVBP may assure substantial and durable benefits in pts with CHF and severe mitral regurgitation (MR). In 25 pts (17M, mean age 64 10 yrs), all with: DCM, LBBB (with or without AV conduction disturbances), MR and CHF (NYHA class 3.2), were implanted with a three chamber DDD pacing system delivering ventricular pacing in two sites: RV apex and RIVS. Before implant and 3, 6, 12 and 18 months after device implantation QRSD, LVEF, MR index (MRI), LVDD and pulmonary arterial pressure (PAP) were measured. Cardiac dynamics during conventional DDD in apex only and DDD-RVBP were evaluated with Tissue echo-Doppler Imaging (TDI). Results achieved with DDD-RVBP pacing are reported in the Table, most of variations between data are statistically significative. TDI showed that DDD-RVBP induces a ventricular resynchronization effect by a shortening both interand intraventricular delays. These data collected in a limited group of pts show that DDD-RVBS induces several benefits: avoids the LBBB induced by pacing; increases LVEF; reduces MR and LVDD; and improves patient’s NYHA functional class. In conclusion, DDD-RVBP improves hemodynamics and quality of life in DCM patient with LBBB and CHF. More pts and a longer follow-up are required to verify if such benefits, demonstrated by other investigators too, will remain stable over a long period of time.

Atrioventricular Node Ablation and Permanent Ventricular Pacemaker Implantation Without Fluoroscopy: Use of an Electroanatomic Navigation System

Non-fluoroscopy AV ablation and pacemaker implantation. Fluoroscopic guidance is the standard tool used for transvenous pacemaker implantations and for electrophysiological and ablation procedures. It implies X-ray exposure, occasionally with high dose of radiation for the patient and operator. We describe the case of a 47-year-old man with uncontrollable permanent atrial fibrillation to whom ablation of the AV conduction and a permanent ventricular pacemaker implantation were successfully performed under the guidance of an electroanatomic navigation EnSite NavX system and with no use of fluoroscopy. This case illustrates the stand-alone use of one of the new non-fluoroscopic navigation systems for a complete procedure such as AV ablation and pacemaker implantation.

Histopathologic characterization of the atrioventricular conduction axis following catheter ablation

Ablation of the AV node with placement of a permanent pacemaker is used for the management of atrial fibrillation with rapid ventricular response refractory to medical therapy. 1 Sousa J. el-Atassi R. Rosenheck S. Calkins H. Langberg J. Morady F. Radiofrequency catheter ablation of the atrioventricular junction from the left ventricle. Circulation. 1991; 84: 567-571 Crossref PubMed Scopus (97) Google Scholar Right-sided radiofrequency (RF) ablation results in successful interruption of AV conduction in 70% to 90% of cases. The retrograde transaortic approach to His-bundle ablation has become an accepted practice when the traditional right-sided approach is ineffective. 2 Kalbfleisch S.J. Williamson B. Man K.C. Vorperian V. Hummel J.D. Calkins H. Strickberger S.A. Langberg J.J. Morady F. A randomized comparison of the right- and left-sided approaches to ablation of the atrioventricular junction. Am J Cardiol. 1993; 72: 1406-1410 Abstract Full Text PDF PubMed Scopus (25) Google Scholar We report a case of penetrating AV bundle ablation using a transseptal approach with histopathologic correlation.

Electrocardiographic Follow‐Up of Biventricular Pacemakers

Multisite pacing for the treatment of heart failure has added a new dimension to the electrocardiographic evaluation of device function. During left ventricular (LV) pacing from the appropriate site in the coronary venous system, a correctly positioned lead V1 registers a right bundle branch block pattern with few exceptions. During biventricular stimulation associated with right ventricular (RV) apical pacing, the QRS is often positive in lead V1. The frontal plane QRS axis is usually in the right superior quadrant and occasionally in the left superior quadrant. Barring incorrect placement of lead V1 (too high on the chest), lack of LV capture, LV lead displacement or marked latency (exit block or delay from the stimulation site), ventricular fusion with the spontaneous QRS complex, a negative QRS complex in lead V1 during biventricular pacing involving the RV apex probably reflects different activation of an heterogeneous biventricular substrate (ischemia, scar, His-Purkinje participation in view of the varying patterns of LV activation in spontaneous left bundle branch block) and does not necessarily indicate a poor (electrical or mechanical) contribution from LV stimulation. In this situation, it is imperative to rule out the presence of coronary venous pacing via the middle cardiac vein or even unintended placement of two leads in the RV. During biventricular pacing with the RV lead in the outflow tract, the paced QRS in lead V1 is often negative and the frontal plane paced QRS axis is often directed to the right inferior quadrant (right axis deviation). In patients with sinus rhythm and a relatively short PR interval, ventricular fusion with competing native conduction during biventricular pacing may cause misinterpretation of the ECG because narrowing of the paced QRS complex simulates appropriate biventricular capture. This represents a common pitfall in device follow-up. Elimination of ventricular fusion by shortening the AV delay, is often associated with clinical improvement. Anodal stimulation may complicate threshold testing and should not be misinterpreted as pacemaker malfunction. One must be cognizant of the various disturbances that can disrupt 1:1 atrial tracking and cause loss of ventricular resynchronization. (1) Upper rate response. The upper rate response of biventricular pacemakers differs from the traditional Wenckebach upper rate response of conventional antibradycardia pacemakers because heart failure patients generally do not have sinus bradycardia or AV junctional conduction delay. The programmed upper rate should be sufficiently fast to avoid loss of resynchronization in situations associated with sinus tachycardia. (2) Below the programmed upper rate. This may be caused by a variety of events (especially ventricular premature complexes and favored by the presence of first-degree AV block) that alter the timing of sensed and paced events. In such cases, atrial events become trapped into the postventricular atrial refractory period at atrial rates below the programmed upper rate in the presence of spontaneous AV conduction. Algorithms are available to restore resynchronization by automatic temporary abbreviation of the postventricular atrial refractory period.

Short Atrioventricular Mahaim Fibers: Observations on Their Clinical, Electrocardiographic, and Electrophysiologic Profile

Short A-V manheim fiber. A short atrioventricular decrementally conducting accessory pathway is an uncommon variant of preexcitation. Available data from small series suggest that their decremental properties might not be caused by A-V nodal-like tissue. We compared clinical, electrocardiographic and electrophysiologic parameters in two groups of patients: 8 patients with a short A-V Mahaim pathway (Group A), and 33 patients with atriofascicular pathways (Group B). Radiofrequency catheter ablation was carried out guided by activation mapping at the annulus in Group A patients and targeting the "M" potential in Group B patients. After ablation of all associated rapidly conducting bypass tracts, 7 of the 8 Group A patients showed clear preexcitation. In only 1 of 8 patients the short A-V Mahaim fiber was actively engaged in a reentrant tachycardia circuit. During radiofrequency catheter ablation an automatic rhythm occurred in 4 of 8 patients. Intravenous adenosine caused conduction a block in the Mahaim fiber in 3 of the 5 patients tested. In group B, no patient showed clear preexcitation (P<00001) while 72% had a minimal preexcitation pattern. Twenty-nine of the 33 patients had a circus movement tachycardia with AV conduction over the atriofascicular fiber. During radiofrequency catheter ablation 30 of 33 patients showed accessory pathway automaticity. Adenosine caused transient block at the atriofascicular pathway in 11 (92%) of the 12 patients tested. While short decrementally conducting right-sided accessory pathways show a typical ECG pattern different from atriofascicular pathways, their electrophysiologic properties do not seem to be uniform. Those pathways can be successfully interrupted by catheter ablation.

Atrioventricular conduction in mammalian species: Hemodynamic and electrical scaling

The purpose of this study was to investigate scaling of the duration of late diastolic left ventricular (LV) filling in relation to AV conduction time (delay) (PR interval on the ECG) in mammals. From mouse to whale, AV delay increases 10-fold, whereas body mass increases one million-fold. The apparent "mismatch" results from scaling of AV delay versus body and heart mass. We measured (1) mitral orifice diameter in 138 postmortem hearts of 48 mammalian species weighing between 17 g and 250 kg and (2) transmitral diastolic flow using magnetic resonance imaging (MRI) recordings of 10 healthy human individuals. (3) We visually inspected early and late diastolic LV filling. (4) We developed two physical models to explain scaling of late diastolic LV filling time. (1) Diameter of the mitral orifice proportionally relates to heart length (third root of heart mass). (2) Atrial contraction starts at a fixed instant (+/- 80%) of the (normalized) cardiac cycle and contributes 31% +/- 5% to LV filling. (3) MRI shows that during diastole, the left atrium (LA) and LV form a single space. (4) The physical models relate the duration of late diastolic LV filling directly to heart length, the third root of heart mass. (1) Late diastolic (LV) filling time scales with heart length (third root of heart mass). (2) No "mismatch" exists between AV delay and heart size. (3) Knowledge of the actual starting time of atrial contraction may contribute to better treatment of patients with heart failure. (4) The findings suggest that in evolution of mammalian species, hemodynamics commands electrical behavior of the heart.