Hemodynamic Findings During Sinus Rhythm, Atrial and AV Sequential Pacing Compared to Ventricular Pacing In a Dog Model

The hemodynamic responses of atrial lAF], atrioventricu-lar sequential (AVP) and ventricuJar pacing (VP) were compared to sinus rhythm (SfiJ in seventeen anesthetized dogs with intact AV conduction. The atrium and/or ventricle were paced at fixed rates above the control sinus rate. An AV interval shorter than normal conduction was selected to capture the ventricle. The changes of pulmonary capillary wedge pressure (PCWP, mmHg). mean aortic pressure (MAP, mmHg), cardiac output (CO, L/min), systemic vascular resistance (SVR, dynes/s/cm⁻⁵), left ventricular stroke work index (SWI) and mean systolic ejection rate (MSER, ml/s) during sinus rhythm, atrial pacing and atrio-ventricular sequential pacing (expressed in percentages of the individual values during ventricular pacing) were:
The importance of atrial systole for cardiac performance was clearly demonstrated in dogs with normally compliant hearts. In both atrial and atrioventricular sequential pacing compared to ventricular pacing there was a reduction of pulmonary capillary wedge pressure (PCWP) (p < 0.01) and systemic vascular resistance (SVR) (p < 0.01) despite an increase in cardiac output (CO). The lesser mean systolic ejection rate (MSER) found during atrioventricular sequential pacing compared to sinus rhythm and atrial pacing may be explained by the abnormal ventricular depolarization in this pacing mode; nevertheless, the mean systolic ejection rate was still greater than that found during ventricular pacing (p < 0.05).     

Severe mitral regurgitation with right ventricular pacing, successfully treated with left ventricular pacing

A case of severe mitral regurgitation with refractory heart failure, after atrioventricular junction ablation and pacemaker implant, was solved with left ventricular pacing. Mitral regurgitation was related to a change in segmental left ventricular motion during right ventricular pacing.     

Determination of the optimal atrioventricular interval in sick sinus syndrome during DDD pacing

BACKGROUND: Although the AAI pacing mode has been shown to be electromechanically superior to the DDD pacing mode in sick sinus syndrome (SSS), there is evidence suggesting that during AAI pacing the presence of natural ventricular activation pattern is not enough for hemodynamic benefit to occur. Myocardial performance index (MPI) is a simply measurable Doppler-derived index of combined systolic and diastolic myocardial performance. The aim of this study was to investigate whether AAI pacing mode is electromechanically superior to the DDD mode in patients with SSS by using Doppler-derived MPI. METHODS: Thirty-nine SSS patients with dual-chamber pacing devices were evaluated by using Doppler echocardiography in AAI mode and DDD mode. The optimal atrioventricular (AV) interval in DDD mode was determined and atrial stimulus-R interval was measured in AAI mode. The ratio of the atrial stimulus-R interval to the optimal AV interval was defined as relative AV interval (rAVI) and the ratio of MPI in AAI mode to that in DDD mode was defined as relative MPI (rMPI). RESULTS: The rMPI was significantly correlated with atrial stimulus-R interval and rAVI (r = 0.57, P = 0.0002, and r = 0.67, P < 0.0001, respectively). A cutoff point of 1.73 for rAVI provided optimum sensitivity and specificity for rMPI >1 based on the receiver operator curves. CONCLUSIONS: Even though the intrinsic AV conduction is moderately prolonged, some SSS patients with dual-chamber pacing devices benefit from the ventricular pacing with optimal AV interval. MPI is useful to determine the optimal pacing mode in acute experiment.     

The influence of atrial and ventricular pacing on the incidence of atrial fibrillation: a meta-analysis

Background: The effect of atrial pacing on the incidence of atrial fibrillation (AF) is unknown. Furthermore, the threshold of ventricular pacing that is associated with a higher incidence of AF has yet to be determined. Thus, we set out to determine the optimal pacing modality in patients with sinus node dysfunction (SND) for the prevention of AF. Methods: Individual patient data from four contemporary pacemaker studies were gathered and analyzed. Since AF would inherently lead to a reduction in atrial pacing, percent atrial and ventricular pacing (%AP and %VP) were determined at the first follow‐up visit and then used as a surrogate for all endpoints. Patients with >5 minutes of AF at the first visit were excluded. The primary endpoint was defined as 7 consecutive days of AF. Results: A total of 1,507 patients were included. During a mean follow‐up of 14.3 ± 8.7 months, 77 patients developed AF (annual rate of 4.3%). The incidence of AF in the first (0–32%), second (32–66%), third (66–89%), and fourth (89–100%) quartiles of %AP was 1.3%, 5.3%, 5.8%, and 8.0%, respectively (P < 0.001). A multivariable analysis found that pacing above the first quartile was associated with a relative risk of 2.93 (95% confidence interval 1.16–7.39, P = 0.023). The grouping of %VP into first (0–2%), second (2–7%), third (7–84%), and fourth (84–100%) quartiles yielded an AF incidence of 2.4%, 3.4%, 6.6%, and 8.0%, respectively (P = 0.001). Conclusion: We demonstrated that in patients with SND both atrial and ventricular pacing are associated with a higher incidence of AF. (PACE 2011; 34:1593–1599)     

Reduction of right ventricular pacing with advanced atrioventricular search hysteresis: results of the PREVENT study

Background: Right ventricular pacing predisposes to the development of heart failure and atrial fibrillation. Automatic atrioventricular search hysteresis (AVSH) is a commonly used strategy to decrease the percentage of right ventricular pacing (%VP) in patients without permanent AV block, but the results have not been optimal. Methods: The randomized, crossover PREVENT study evaluated whether an enhanced AVSH with two new features can reduce %VP compared with standard AVSH. The new features are the repetitive hysteresis [switch from extended to basic AV delay after a consistent loss of intrinsic AV conduction (IAVC) lasting for six consecutive atrial cycles] and the scan hysteresis (periodic IAVC search extension over six consecutive atrial cycles). Both standard AVSH and enhanced AVSH performed a periodic IAVC search every 180 cardiac cycles and operated with a basic AV‐delay of 225 ms and a rate‐independent maximum AV‐delay of 300 ms for paced and sensed atrial events. Results: Among 178 patients, 53.4% had no evidence of AV block at enrollment and 46.6% had history of intermittent AV block. The median %VP was decreased by enhanced AVSH compared to standard AVSH (4.0% vs 5.5%, P < 0.001), particularly in patients with a history of AV block (21.4% vs 25.5%, P < 0.001). The primary study hypothesis that 25% of all patients would experience > 20% relative %VP reduction was not met as 46 (25.8%) patients (95% confidence interval, 20.5–31.8%) presented such relative reduction. Conclusion: The enhanced AVSH algorithm reduces %VP compared with standard AVSH in patients with intermittent AV block. (PACE 2011; 34:975–983)     

Microdislodgment of ventricular pacing lead undetectable during rapid pacing one year after implantation

A 71-year-old woman had undergone valvular heart surgery in 1981, and implantation of a permanent ventricular pacemaker for ventricular pauses during atrial fibrillation in 2001. One year after pacemaker implantation, she complained of faintness. When pacing at 100 beats/min the pacemaker functioned properly. However, pacing and sensing failure was detected at a pacing rate of 60 beats/min. At rapid pacing rates, the lead tip was in closer contact with the endocardium, and its microdislodgment was undetectable. The symptoms have resolved since the lead was repositioned.     

Increased capture threshold in permanent His-bundle pacing associated with flecainide

A 64-year-old man underwent implantation of a permanent His-bundle pacemaker. A marked rise in the selective His-bundle capture threshold was noted 1 month after the patient started flecainide acetate for rhythm control of recurrent, symptomatic atrial flutter and atrial fibrillation. The capture threshold subsequently normalized 4 days after discontinuing flecainide and switching to dofetilide. To our knowledge, this is the first documented case of a rise in selective His-bundle capture threshold associated with flecainide acetate. Further studies are needed to characterize this association which could result in higher capture thresholds, decreased battery longevity, and mimic His-bundle lead failure.     

Effects of continuous and triggered atrial overdrive pacing on paroxysmal atrial fibrillation in pacemaker patients

Background: The aim of the study was to compare the effects of different pacing strategies to prevent paroxysmal atrial fibrillation (AF): triggered atrial overdrive pacing versus the combination of triggered and continuous overdrive pacing.
Methods : Patients with an indication for dual-chamber pacing (Selection 9000, Prevent AF; Vitatron B.V., Arnhem, the Netherlands) and a history of paroxysmal AF were randomized to triggered atrial pacing (three pacing functions, "triggered group": PAC Suppression™, Post-PAC Response™, and Post-Exercise Response™) or to the combination of continuous (Pace Conditioning™) and triggered atrial pacing (four pacing functions, "combined group"). After 3 months, there was a crossover to the other pacemaker setting.
Results : In 171 enrolled patients, the median AF burden of the combined group was with 2.1% versus 0.1% in the triggered group (P = 0.014). Fewer AF episodes were observed in the triggered (median: 7) than in the combined group (median: 116; P = 0.016). The combined group had more frequent atrial pacing (median 97%) than the triggered group with 85% (P < 0.001), but ventricular pacing was not significantly different with 95% and 96% in the combined and triggered group, respectively. After the crossover, the AF burden increased in the triggered group to 0.3% and decreased in the combined group to 0.4%.
Conclusions : Triggered atrial pacing functions alone resulted in a low AF burden. The additional activation of continuous atrial overdrive pacing increased the percentage of atrial pacing, but had no beneficial effects on the prevention of paroxysmal AF.     

Asynchronous ventricular pacing: a rare cause of ventricular tachycardia

Asynchronous cardiac pacing may induce ventricuiar tachycardia and fibrillation, particularly in patients with ischemic heart disease and possibly other types of myocardial abnormalities. All patients with implanted asynchronous pacemakers, and those whose demand pacemakers operate in asynchronous mode for any reason, are to he considered at risk from this complication. In patients with serious myocardial abnormalities consistent demand pacing should be assured, even if it requires early pacemaker replacement. Anti-arrhythmic agents may prove useful for temporary suppression of pacemaker-induced arrhythmias. (PACE, Vol. 5, July-August, 1982)     

Single-chamber leadless pacemaker for atrial synchronous or ventricular pacing

Leadless pacing is a major breakthrough in the management of bradyarrhythmia. Results of initial clinical trials that have demonstrated a significant reduction in acute and long-term pacing-related complications have been confirmed by real-world experience in a broader spectrum of patients. Nonetheless current use of a leadless pacemaker is hampered by its limited atrial sensing and pacing capability, as well as battery life-span and retrievability. We review the current clinical outcome data, indications and contraindications, implantation and retrieval techniques, synchronous ventricular pacing, and other clinical considerations. We also provide an overview of the latest advancements in leadless pacing technology including device-to-device communication and energy harvesting technology.     

病态窦房结综合征伴房室传导延迟AAI与DDD起搏模式右心功能的超声评价

目的探讨AAI与DDD起搏模式下病态窦房结综合征伴房室传导阻滞患者的右心功能。方法 35例病态窦房结综合征伴Ⅰ度房室传导阻滞植入DDD双腔起搏器患者,先用程控仪将起搏器程控为DDD模式,最后程控为AAI模式。超声心动图检测患者2种起搏模式下的各参数变化情况。结果 DDD起搏模式下的RVPEP、RVPEP/RVET、Sm、Tei指数明显高于AAI起搏模式（P〈0.05）,E/Em低于AAI起搏模式（P〈0.05）。结论 AAI起搏模式右心的收缩和舒张功能均优于AV间期优化的DDD起搏模式。     

Physiologic pacing: new modalities and pacing sites

Right ventricular (RV) apical pacing impairs left ventricular function by inducing dys-synchronous contraction and relaxation. Chronic RV apical pacing is associated with an increased risk of atrial fibrillation, morbidity, and even mortality. These observations have raised questions regarding the appropriate pacing mode and site, leading to the introduction of algorithms and new pacing modes to reduce the ventricular pacing burden in dual chamber devices, and a shift of the pacing site away from the RV apex. However, further investigations are required to assess the long-term results of pacing from alternative sites in the right ventricle, because long-term results so far are equivocal. The potential benefit of prophylactic biventricular, mono-chamber left ventricular, and bifocal RV pacing should be explored in selected patients with a narrow QRS complex, especially those with impaired left ventricular function. His bundle pacing is a promising and evolving technique that requires improvements in lead technology.     

Evaluation of the early hemodynamic changes in carotid arteries during ventricular and dual chamber pacing

In spite of a wide choice of pacemakers, there are some problems in making more rational clinical decisions for individual patients since mode selection and programming is usually performed on the basis of a clinical hunch. The aim of this study was to measure the differences in carotid flow in patients with a pacemaker programmed in the dual chamber and in the single chamber pacing modes. Sixty patients with implanted bipolar DDD pacemakers were enrolled in this study. Blood peak systolic velocity (PSV) and end-diastolic velocity (EDV), cross-sectional area, resistive index (RI), and pulsatility index (PI) were measured in the common (CCA), internal (ICA), and external (ECA) carotid arteries before pacemaker implantation and after dual chamber and ventricular pacing at 60 beats/min. PSVs in the left CCA (79.3 +/- 24.9 cm/s) and right CCA (84.1 +/- 18.7) were shown to significantly decrease after VVI pacing (60.1 +/- 16.6 and 62.1 +/- 20.0, respectively). There was also a similar significant decrease in PSV in the left and right ICAs and ECAs. Besides PSV, RI, and PI in the left and right CCAs, ICAs, and ECAs significantly decreased after VVI pacing. There was no similar decrease after DDD pacing. Cross-sectional area and flow volume in the CCA, ICA, and ECA were similar after DDD and VVI pacing and before pacemaker implantation suggesting that cardiac output was similar when the measurements were recorded. Carotid artery PSVs, pulsatility, and RIs were found to be significantly decreased during VVI pacing compared to baseline and DDD pacing. The greater incidence of adverse cerebral outcomes in patients with VVI rather than DDD pacing may be partly due to decreased carotid PSVs.     

Reduction of right ventricular pacing in patients with sinus node dysfunction using an enhanced search AV algorithm

BACKGROUND: 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. METHODS: 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. RESULTS: 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%. CONCLUSIONS: 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.     

Acute Hemodynamic Effects of Alternate and Combined Site Pacing in Patients after Cardiac Surgery

We hypothesized that pacing at sites other them the right ventricular (RV) apex or at two or more ventricular sites would activate the myocardium more rapidly and improve cardiac function in patients undergoing coronary revascularization or aortic valve replacement. Epicardial electrodes were placed on the right atrium (A), RV paraseptal area close to the RV apex (B), RV outflow tract (C), LV apex (D), in patients undergoing bypass surgery. At constant rate and AV delay, we measured CO during A pacing, DV1 pacing at B, C, D, and various combinations of sites in random order in ten patients with EF > 50% and 27patients with EF ≤ 50%. When pacing at two sites, we made one electrode a cathode and one an anode and noted two distinct thresholds by careful observation of the 12-lead ECG. There were no significant differences in CO, systemic vascular resistance, systolic, or mean arterial pressure. Significant differences were noted in QRS duration, which increased progressively going from AAI to 3-site, 2-site, and single site pacing (P < 0.05 each comparison). Thus: (1) QRS duration correlated inversely with the number of ventricular sites paced; (2) despite this, CO did not improve irrespective of baseline EF; (3) multisite pacing produced multiple distinct thresholds which appeared to be related to the number of sites paced, and (4) unique ECG patterns confirmed multisite pacing.     

Validation of dual-chamber pacemaker diagnostic data using dual-channel stored electrograms

BACKGROUND: Pacemaker diagnostic counters are used to guide device programming and patient management. However, these data are susceptible to inappropriate classification of events. The aim of this multicenter study was to evaluate pacemaker diagnostic data using stored intracardiac electrograms (EGMs). METHODS: The study included 351 patients (191 males, aged 71 +/- 10 years) with standard indications for dual-chamber pacemaker implantation. EGM triggers were atrial tachycardia (AT), ventricular tachycardia (VT), sudden bradycardia response (SBR), and pacemaker-mediated tachycardia (PMT). For this study, the devices could store up to 5 EGMs of 8s each (with marker annotation and onset recording). After 3 months, the EGMs were analyzed and classified as "confirmed" if the EGM validated the trigger and as "false positive" if the EGM showed an event different from the trigger. RESULTS: Of the 1,003 EGMs available, the triggers were AT in 640 EGMs, VT in 76, SBR in 105, and PMT in 178 EGMs. Four EGMs were triggered by magnet application. The trigger was confirmed in 614 EGMs (62%): 62% of AT episodes, 18% of VT episodes, 100% of SBR episodes, and 54% of PMT episodes. In 385 cases (45%), the EGMs revealed false-positive events due to far-field sensing (39%), noise and myopotential sensing (26%), sinus tachycardias (21%), double counting (9%), exit block (4%), and undersensing (1%). CONCLUSION: This large-scale study of stored EGMs revealed their value in validating diagnostic counter data. Therapeutic decisions should not be based on diagnostic counters alone; they should be validated by sophisticated tools like stored EGMs.     

Right ventricular outflow tract endocardial pacing complicated by intercostal muscle twitching

A recipient of a dual-chamber pacing system, with a bipolar endocardial lead screwed into the right ventricular outflow tract (RVOT), developed intercostal muscle twitching. No lead perforation was identified. This observation suggests that meticulous attention should be paid to this potential complication when choosing the RVOT as a site of permanent endocardial pacing.     

Implantation of a dual-chamber pacemaker in a patient with dextrocardia and sick sinus syndrome: a case report

Dextrocardia is a congenital abnormal position of the heart in which the main part of the heart is in the right chest, and the long axis of the heart points to the lower right. Cases of a combination of dextrocardia and sick sinus syndrome are rare. A 65-year-old female patient was admitted to hospital with palpitations and dizziness for 1 week. Mirror-image dextrocardia and sick sinus syndrome were diagnosed by an electrocardiogram, echocardiography, Holter monitoring, and X-rays. Finally, we successfully implanted a dual-chamber pacemaker into the patient. The patient had an uneventful recovery and was discharged when her symptoms had greatly improved 1 week later. When dextrocardia is present, using active fixation leads in the atrial and ventricular leads is easier for finding the pacing position with optimal sensing and pacing thresholds, and they reduce the incidence of falling off.