Pacing Pulse Research Articles

Transient pacing pulse on the T-wave: What is the mechanism?

A patient with a dual-chamber pacemaker for sick sinus syndrome was hospitalized for heart failure. The electrocardiography (ECG) during hospitalization displayed seemingly abnormal pacing artifacts. This report focuses on the problem-solving of an abnormal-looking paced ECG and identifies the pacemaker's operational behavior as the underlying reason.

Pacing on the tail of paced QRS: What is the mechanism?

An electrocardiogram on the day after implantation of a dual-chamber pacemaker revealed 2 closely coupled pacing spikes at 100-ms intervals, with the latter being on the trailing edge of the paced QRS complex. Differential diagnoses of such closely coupled pacing pulses include atrial lead displacement, lead reversal on the pulse generator, ventricular premature complex in the post–atrial ventricular blanking period, and backup pacing pulse following a loss of capture. Critical analysis of the pacemaker timing intervals led to the mechanism and cause of the problem.

High-Energy Pacing in the Jejunum Elicits Pulsatile Segmental Contractions.

Compromised bowel function is associated with a range of motility disorders such as post-operative ileus and chronic intestinal pseudo-obstruction. Disordered or weak motility compromise the efficient movement of luminal contents necessary for digestion and nutrient absorption. This study investigated the potential of high-energy pacing to enhance contractions in the proximal jejunum of the small intestine. Pacing pulse parameters (pulse-width: 100 ms, 200 ms, 400 ms, pulse-amplitude: 4 mA, 6 mA, 8 mA) were systematically varied in the in vivo porcine jejunum (n = 7) and the induced contractile responses were evaluated using a video mapping system. Localized segmental contractions were quantified by measuring the intestinal diameter and thereby computing the strain. The impact of pacing parameters on contractile strain was investigated. Finally, histological studies were conducted on paced tissue to assess for potential tissue damage. Segmental contractions were successfully induced at all pulse-settings and evaluated across 67 pacing sessions. In response to pacing, the intestine segment at the site of pacing contracted, with diameter reduced by 6-18%. Contractile response significantly increased with increasing pulse-amplitude. However, with increasing pulse-width, the increase in contractile response was significant only between 100 ms and 400 ms. Histology showed no tissue damage occurred when maximal pacing energy (pulse-amplitude = 4-8 mA, pulse-width = 400 ms, 5 minute duration) was applied. High-energy pacing induced periodic segmental contractions in response to pacing pulses and the contractile strain was proportional to the energy applied on the intestine. The ability to enhance motility through pacing may hold promising therapeutic potential for bowel disorders and awaits clinical translation. Small intestine pacing elicits localized segmental contractions which increase in magnitude with increasing pulse settings. This study marks the first adaptation of video mapping techniques to track the pacing response in the small intestine.

Abstract 13899: Engineered Tissue Graft Electrically Couples With Swine Host Heart

Introduction: Adult mammalian hearts are unable to replenish myocytes lost in myocardial infarction (MI). Recent therapies that implant myocytes derived from human induced pluripotent stem cells (hiPSC-CMs) have shown structural integration of the graft, improved cardiac function, and reduced scar size. However, to successfully remuscularize the heart, implanted tissue must integrate electrically. Here, we directly image electrical coupling between engineered grafts and the host. Methods: We created anterior LV MI in 3 immunosuppressed pigs using ischemia-reperfusion. Cardiac spheroids engineered from hiPSC-CMs were implanted into the border zone right after the procedure. Spheroids were transfected with a calcium indicator (GCaMP6). One week post implantation, the animal was sacrificed, and 0.6 mm thick slices of myocardium containing spheroids were obtained (Fig. A). The slices were stained with a voltage-sensitive dye (VSD) for optical mapping. GCaMP6 and the VSD have different emission spectra allowing electrical activation of the host tissue and spheroids to be imaged independently. The slices were activated with both global field stimuli and focal stimuli applied distant from the spheroids. Results: During field stimulation, action potentials in the slice and calcium transients (CaT) in the spheroids were simultaneous. However, during focal pacing, there was propagation across the slices and latency between the pacing pulses and spheroid CaTs (Fig. B, C). This indicates spheroid activation arose from electrical coupling with the host myocardium and not from direct stimulation by the pacing pulse. We observed coupling at 12 spheroid sites in 10 slices. At 6 sites, 1:1 coupling could be maintained at pacing rates up to 4 Hz (Fig. D). Conclusions: To our knowledge, this is the first demonstration of swine host myocardium coupling electrically with a human engineered tissue graft. Coupling occurred within 1 week and enabled the host to drive the graft.

Evaluation of Pacing Parameters to Induce Contractions in the Small Intestine.

Postoperative ileus and chronic intestinal pseudo-obstruction are intestinal motility disorders that can compromise bowel function resulting in a significant reduction in quality of life and prolonged hospital stays. While medication and nutritional support provides relief for some patients, a significant patient population remains untreated. Therefore, alternative treatment options are required. A novel framework that enables small intestine pacing and video mapping of the contractile response was developed. Pacing pulse parameters (pulse-period: 2.7, 10 s, pulse-width: 100, 400 ms, and pulse-amplitude: 4, 6, 8 mA) were systematically varied to investigate the effect of pacing on the small intestine contractility. The contractile response was quantified by computing the strain of the intestinal diameter at the pacing site. The framework was applied in vivo on porcine jejunal loops (n=4) where segmental contractions were induced in response to pacing pulses. Strain increased with increasing pulse-amplitude and pulse-width, while pacing at a period of 2.7 s elicited higher contractile strains compared to pacing at a period of 10 s at all settings (e.g., -0.18 ± 0.06 vs 0.12 ± 0.06 at 8 mA, 400 ms). For a pulse-width of 100 ms, the contractile strain continued to increase with increasing pulse-amplitude, while the induced strain was comparable for all pulse-amplitudes when paced with high pulse-width (400 ms). Therefore, pacing is an effective tool in modulating the intensity of segmental contractions.Clinical Relevance- Different pacing parameters can define contraction intensity and frequency in the small intestine. This is of therapeutic potential for treating motility disorders such as post-operative ileus and chronic intestinal pseudo-obstruction.

Successful Clindamycin Therapy of an Infected Subcutaneous Permanent Pacing Lead in a Dog after a Failed Course with Potentiated Amoxicillin and Enrofloxacin

Though permanent pacemaker implantation is the only effective therapy for certain bradyarrhythmias in dogs, it is not without risks. Bacterial infection of the device is one of the most common complications. Human guidelines recommend besides systemic antibiotics, surgical explantation of the pacing lead and pulse generator in case of device-infection. This report describes a 13.5-year-old dog that received a transvenous endocardial permanent pacemaker because of syncopal episodes resulting from paroxysmal third-degree atrio-ventricular block. Five days after an uneventful surgery, a painful swelling appeared around the subcutaneous part of the lead where this was inserted into the jugular vein. A 4-week course of amoxicillin and clavulanic acid combined with enrofloxacin failed to clear the infection on long-term. Ultrasound-guided puncture of the abscess was performed to gain a sample for bacterial culture and antibiogram. Oral clindamycin of 4 weeks' duration successfully resolved the infection with Staphylococcus aureus without having to explant the device. Repeated ultrasonographic examinations and fine-needle aspiration biopsies were used to evaluate for persistent local inflammation, guiding the length of the antibiotic therapy. Though the described approach has traditionally been ill-advised because of the risk of introducing bacteria and damaging the pacemaker lead, it was successful in our case.

Design and Stability Analysis of an Adaptive Neuro-Fuzzy Inference System (ANFIS)-Based Pacemaker Controller in MATLAB Simulink.

We present the design and stability analysis of an adaptive neuro-fuzzy inference system (ANFIS)-based controller of a pacemaker in MATLAB Simulink. ANFIS uses learning and speed properties of fuzzy and neural networks. Based on body states and preprogrammed situations of patients (age and sex, etc.), heart rate and amplitude of pacing pulse are changed. Output signal that is fed backed from heart is compared to the reference fuzzy bases ANFIS signals. After designing ANFIS based controller, the stability of the proposed system has been tested in both the time (step response) and trequency (Bode diagram and Nichols chart) domains. In our previous study, the step response analyzed and compared with other works. For frequency domain, all the possible frequency analysis methods have been tested but because of nonlinear properties of ANFIS, after linearization, just the Bode diagram achieved good results. The step response results in time domain is compared with previous work's results including optimum heart pulse rate for each particular patient. In the frequency domain, the Bode diagram stability analysis showed gain and phase margin as follows: GM (dB) = 42.1 and PM (deg) = 100.

PO-687-07 NOVEL PACING TECHNIQUE FOR A PATIENT WITH COMPLETE HEART BLOCK AND NO VENOUS ACCESS, UTILIZING THE WISE-CRT SYSTEM

n/a Wise-CRT for unconditional pacing n/a 30-year-old man with medical history significant for hypertension, system lupus, coronary artery disease s/p CABG in 2019, chronic kidney disease on hemodialysis, with multiple dialysis catheter placement in the past, currently has a transhepatic catheter, which has gotten infected multiple times, who presented after a syncope episode, and found to be in complete heart block with junctional escape rhythm at 35 bpms. Attempts to implant a leadless pacemaker was unsuccessful because both his common iliacs (right and left) were completely closed likely because of multiple dialysis catheter placement, decision was made to go to the right internal jugular however again his SVC was chronically closed. At this point the patient had two options, wither to have a transhepatic approach and place a ventricular lead through that access however, given his infection history with MRSA, VRE, and multiple transhepatic catheter infection it would be inevitable for him to develop endocarditis, or to have an epicardially placed leads. He was taken to the OR and THREE epicardial leads were placed, one of which was capturing in the OR with acceptable thresholds ∼ 2 mV however next day, non or the three epicardial leads are capturing and the patient remains in complete heart block with junctional escape rhythm at 35 beats per minutes. FDA compassionate one time use and IRB approval were obtained. In this case, the novel pacing techniques was implanting Wise-CRT system via a retrograde aortic access, and placed in the lateral wall of the left ventricular endocardially under TEE and Fluoroscopy Guidance (Picture). The device transmitter programmed to sense the pacing pulse (spikes) from currently placed non-capturing epicardial lead and send ultrasound energy signals to the endocardiac receiver electrode which in turn paced the ventricular. Procedure was done successfully without any complications. Wise-CRT can be used as a single pacing system in patient with no Venous Access

Interactive Effects of HRV and P-QRS-T on the Power Density Spectra of ECG Signals.

Different from the traditional methods of assessing the cardiac activities through heart rhythm statistics or P-QRS-T complexes separately, this study demonstrates their interactive effects on the power density spectrum (PDS) of ECG signal with applications for the diagnosis of ST-segment elevation myocardial infarction (STEMI) diseases. Firstly, a mathematical model of the PDS of ECG signal with a random pacing pulse train (PPT) mimicking S-A node firings was derived. Secondly, an experimental PDS analysis was performed on clinical ECG signals from 49 STEMI patients and 42 healthy subjects in PTB Diagnostic Database. It was found that besides the interactive effects which are consistent between theoretical and experimental results, the ECG PDSs of STEMI patients exhibited consistently significant power shift towards lower frequency range in ST-elevated leads in comparison with those of reference leads and leads of health subjects with the highest median frequency shift ratios at 51.39 ± 12.94% found in anterior MI. Thirdly, the results of ECG simulation with systematic changes in PPT firing statistics over various lengths of ECG data ranging from 10 s to 60 mins revealed that the mean and median frequency parameters were less affected by the heart rhythm statistics and the data length but more depended on the alterations of P-QRS-T complexes, which were further confirmed on 33 more STEMI patients in European ST-T Database, demonstrating that the frequency indexes could be potentially used as alternative indicators for STEMI diagnosis even with ultra-short-term ECG recordings suitable for wearable and mobile health applications in living-free environments.

Stimulation and propagation of activation in conduction tissue: Implications for left bundle branch area pacing

Characterizing wavefront generation and impulse conduction in left bundle (LB) has implications for left bundle branch area pacing (LBBAP). The purpose of this study was to describe the pacing characteristics of LB and to study the role of pacing pulse width (PW) in overcoming left bundle branch block. Twenty fresh ovine heart slabs containing well-developed and easily identifiable tissues of the conduction system were used for the study. LB stimulation, activation, and propagation were studied under baseline conditions, simulated conduction slowing, conduction block, and fascicular block. The maximum radius of the LB early activation increased up to 13.4 ± 2.4 mm from the pacing stimulus, and the time from stimulus to evoked potential shortened when pacing PW was increased from 0.13 to 2 ms at baseline. Conduction slowing and block induced by cooling could be resolved by increasing pacing PW from 0.25 to 1.5 ms over a distance of 10 ± 1.5 mm from the pacing stimulus. The LB strength-duration (SD) curve was shifted to the left of the myocardial SD curve. Increasing PW resolved conduction slowing and block and bypassed the experimental model of fascicular block in LB. Precise positioning of the LB lead in left ventricular subendocardium is not mandatory in LBBAP, as the SD curve of LB was shifted to the left of the myocardium SD curve and could be captured from a distance by optimizing PW.

An in vitro Evaluation of the Effect of Transient Electromagnetic Fields on Pacemakers and Clinical Mitigation Measures

Background: The effect of transient electromagnetic fields on the function of pacemakers is not well-evaluated. There is a lack of effective methods for clinicians to reduce electromagnetic susceptibility (EMS) during implantation of pacemakers. This study aimed to evaluate whether a novel method of handling the excess leads in the pocket can lower the EMS of pacemakers and consequently reduce the effect of electromagnetic interference caused by transient electromagnetic fields on pacemakers.Methods: An in vitro chest model was established to simulate the clinical condition of dual-chamber pacemaker implantation. Three different intertwining patterns of excess leads were examined: parallel, twisted once, and multiple twisted-pair. Oscillated currents were injected into a copper electrical wire set horizontally above the model to create a radiated magnetic field to simulate the transient daily electromagnetic exposure of pacemakers. The electromagnetic induction of current was measured. The occurrence of EMS-related adverse events was evaluated when the induced pulsed voltage was applied.Results: Transient electromagnetic fields can induce electromagnetic noise in the pacing loop and inhibit the release of pacing pulses. The multiple twisted-pair intertwining pattern of excess leads was associated with a lower induced voltage amplitude than both the parallel and once-twisted patterns (P < 0.001). Even once twisted could significantly reduce induced voltage amplitude compared to not twisted (P < 0.001). A lower incidence of pacing inhibition was also observed in the multiple twisted-pair group than in the other two groups (P < 0.001).Conclusions: Transient electromagnetic fields can cause pacing inhibition. Twisting the excess leads for multiple turns in the pocket is an effective method to reduce the EMS of the dual-chamber pacemaker.

The radiofrequency interference on CRT-D functioning during AV node ablation: An educational case.

We have described some unusual findings of radiofrequency interference with ICD functioning during AV nodal ablation, guiding the reader to the possible explanation of the phenomena.

Investigation of safety for electrochemotherapy and irreversible electroporation ablation therapies in patients with cardiac pacemakers

BackgroundThe effectiveness of electrochemotherapy of tumors (ECT) and of irreversible electroporation ablation (IRE) depends on different mechanisms and delivery protocols. Both therapies exploit the phenomenon of electroporation of the cell membrane achieved by the exposure of the cells to a series of high-voltage electric pulses. Electroporation can be fine-tuned to be either reversible or irreversible, causing the cells to either survive the exposure (in ECT) or not (in IRE), respectively. For treatment of tissues located close to the heart (e.g., in the liver), the safety of electroporation-based therapies is ensured by synchronizing the electric pulses with the electrocardiogram. However, the use of ECT and IRE remains contraindicated for patients with implanted cardiac pacemakers if the treated tissues are located close to the heart or the pacemaker. In this study, two questions are addressed: can the electroporation pulses interfere with the pacemaker; and, can the metallic housing of the pacemaker modify the distribution of electric field in the tissue sufficiently to affect the effectiveness and safety of the therapy?ResultsThe electroporation pulses induced significant changes in the pacemaker ventricular pacing pulse only for the electroporation pulses delivered during the pacing pulse itself. No residual effects were observed on the pacing pulses following the electroporation pulses for all tested experimental conditions. The results of numerical modeling indicate that the presence of metal-encased pacemaker in immediate vicinity of the treatment zone should not impair the intended effectiveness of ECT or IRE even when the casing is in direct contact with one of the active electrodes. Nevertheless, the contact between the casing and the active electrode should be avoided due to significant tissue heating at the site of the other active electrode for the IRE protocol and may cause the pulse generator to fail to deliver the pulses due to excessive current draw.ConclusionsThe observed effects of electroporation pulses delivered in close vicinity of the pacemaker or its electrodes do not indicate adverse consequences for either the function of the pacemaker or the treatment outcome. These findings should contribute to making electroporation-based treatments accessible also to patients with implanted cardiac pacemakers.

Electrode Model and Simulation of His- Bundle Pacing for Cardiac Resynchronization Therapy

Abstract A disturbed synchronization of the ventricular contraction can cause a highly developed systolic heart failure in affected patients with reduction of the left ventricular ejection fraction, which can often be explained by a diseased left bundle branch block (LBBB). If medication remains unresponsive, the concerned patients will be treated with a cardiac resynchronization therapy (CRT) system. The aim of this study was to integrate His-bundle pacing into the Offenburg heart rhythm model in order to visualize the electrical pacing field generated by His-Bundle-Pacing. Modelling and electrical field simulation activities were performed with the software CST (Computer Simulation Technology) from Dessault Systèms. CRT with biventricular pacing is to be achieved by an apical right ventricular electrode and an additional left ventricular electrode, which is floated into the coronary vein sinus. The non-responder rate of the CRT therapy is about one third of the CRT patients. His- Bundle-Pacing represents a physiological alternative to conventional cardiac pacing and cardiac resynchronization. An electrode implanted in the His-bundle emits a stronger electrical pacing field than the electrical pacing field of conventional cardiac pacemakers. The pacing of the Hisbundle was performed by the Medtronic Select Secure 3830 electrode with pacing voltage amplitudes of 3 V, 2 V and 1,5 V in combination with a pacing pulse duration of 1 ms. Compared to conventional pacemaker pacing, His-bundle pacing is capable of bridging LBBB conduction disorders in the left ventricle. The His-bundle pacing electrical field is able to spread via the physiological pathway in the right and left ventricles for CRT with a narrow QRS-complex in the surface ECG.

Effect of Percentage Reduction in Action Potential Duration of M-cells on Re-entry in Short QT Syndrome.

Increase in transmural dispersion of repolarisation along with a diminished QT interval have been known to aid in the development of arrhythmia during KCNQ1-linked short QT syndrome type 2 (SQTS2). However, the percentage by which action potential duration (APD) shortens in the different cell types that make up the ventricular wall are not fully understood. In this study, the percentage of APD shortening of M-cells was varied to determine the conditions under which re-entry occurs during SQTS2. A 2D transmural section of the heart with anisotropic properties is considered. Slight modifications to the TP06 equations are used to simulate the electrophysiology of the endocardial (endo), midmyocardial (M) and epicardial (epi) cells. A discrete network of 250×100 cells are interconnected using gap junction conductances and from this, a pseudo ECG is generated. On pacing the tissue with premature beats in the midst of normal pacing pulses and on including SQTS, it is observed that re-entry is sustained for a longer duration when the APD shortening in M-cells is more compared to the epi or endo cells while the percentage reduction in APD of M-cells is about 5% to 7% lesser than that in epi and endo cells. Further, when the percentage reduction in APD of M-cells is similar to epi or endo cells, no re-entry is generated. This analysis highlights the key role of percentage reduction in APD of M-cells compared to epi and endo cells in maintaining the re-entrant waves.

Proarrhythmic effect of automatic threshold testing algorithm in dual chamber devices.

Operation of auto-threshold testing (ATT) algorithmin current dual chamber cardiac devices require temporary shortening of atrio-ventricular (AV) delay to accurately measure evoked potential (capture) after a pacing pulse. Near simultaneous AV pacing causes atrial pressure elevation and may be associated with atrial arrhythmias. We evaluated the prevalence of atrial arrhythmias induced by ATT in Abbott devices. Device clinic records were reviewed at a single center for patients with dual chamber Abbott pacemaker/ICD. ATT-induced atrial fibrillation (AF)cases were defined as new appropriate mode switch episodes while the ATT was operating. The auto-capture test trends were defined as unstable if there were deviations >1 V in capture threshold trend events that did not correlate with routine in-office testing. One hundred and seventy patients were programmed in dual chamber pacing mode. The ventricular ATT was active in 118 patients and of these 78 had true mode switch episodes. Six patients developed AF during ventricular ATT. Three patients had most recorded atrial arrhythmias in close association with ATT (63%, 66%, 100% vs2%,9%, 33% in other patients with known prior AF). An unstable auto-capture trend curve was seen in 33 patients (6 showing ATT-induced AF) versus85 patients with stable auto-capture curve and no ATT-induced AF (P = .0001, the χ2 test). Ventricular auto-capture algorithm use is associated with induction of AF in dual chamber Abbott devices with a prevalence of over 5%. AF occur more frequently (18%) in patients with erratic ventricular ATT trend results.

P1488Autonomic nervous system optimized cardiac resynchronization therapy

Abstract Introduction. Traditional Cardiac Resynchronization Therapy, CRT, relies on bi-ventricular, bi-V, pacing. For left bundle branch block, LBBB, patients with good atrial-right ventricular conduction, A-RVc, alternatives have been proposed that use left-ventricular only pacing, LVoP, with adaptive atrio-ventricular delay, AVD, that is updated every minute from A-RVc measurements. The key advantage is extended device longevity since the RV pacing pulse is not emitted. Purpose. In this paper we present a CRT alternative using fixed AVD LVoP + RV sense trigger (an LV pulse is triggered when an RV depolarization is sensed), RVsT, that can be used with LBBB patients with good A-RVc. Intrinsic RV depolarization is used. The longevity of the device is expected to approach that of a dual chamber device since AVD adaption is not needed. Method. 5 CRT patients with LBBB and good A-RVc, previously programmed to bi-V pacing, were reprogrammed to fixed AVD LVoP + RVsT. The devices are standard CRT pacemakers, CRT-P, with RVsT. They are normally operated in LVoP mode. In response to atrial tachycardia, mode switching to bi-V will be required. So, 3 chamber devices are still required. Results. Nightly at about 02:00 the CRT-P collects Ax-Vs (Ax = As &amp; Ap) statistics for 35 consecutive heart cycles with AVD of 300 ms, while the patient is asleep. A typical plot of these timing statistics at the time of reprogramming to LVoP is shown in Fig. 1. After a self-training period of 2 weeks to 9 months, these statistics coalesce in a narrow range of values, 20 ms wide, as illustrated in Fig. 2 for our super responder (2 weeks). This 20 ms wide pattern persisted for the next 9 months. In the case of the index patient this lasted 3+ years. This persistent A-RVc pattern across all 5 patient can only be explained by a tight dromotropic control by the Autonomic Nervous System, ANS. Fig. 3 illustrates RVsT. As the RVs arrives earlier than the LVp, there is no longer synchronicity improvement since the LVp now follows the RVs immediately. In Fig. 4, we see long periods with high %RVs associated with high heart rates. Increased hemodynamic demand can only be met by increased contractility. Thus inotropic modulation by the ANS is now active and effective. The patients were put on remote monitoring with nightly follow-ups. Over a period of 6.5 months RVs (pre LVp) statistics were collected. A daily median of 11% was reported for this patient. On a particular day, it can be as high as 50%. Dromotropic action to pull in the RVs cannot be explained without concurrent inotropic modulation. Conclusions. Traditional CRT leads to ineffective ANS modulation due to bi-V pacing for &amp;gt;95-98% of the cycles. In our 5 patients the fixed AVD LVoP + RVsT program has allowed nervous system remodeling and the ANS is back in control of hemodynamics. Thus we have ANS optimized CRT! It is an attractive CRT alternative for LBBB patients with good A-RVc since device longevity is also improved. Abstract Figure. Fixed delay LV-only + RVs trigger

Real-Time Closed-Loop Suppression of Repolarization Alternans Reduces Arrhythmia Susceptibility In Vivo.

Repolarization alternans (RA) has been implicated in the pathogenesis of ventricular arrhythmias and sudden cardiac death. We have developed a real-time, closed-loop system to record and analyze RA from multiple intracardiac leads, and deliver dynamically R-wave triggered pacing stimuli during the absolute refractory period. We have evaluated the ability of this system to control RA and reduce arrhythmia susceptibility, in vivo. R-wave triggered pacing can induce RA, the magnitude of which can be modulated by varying the amplitude, pulse width, and size of the pacing vector. Using a swine model (n=9), we demonstrate that to induce a 1 µV change in the alternans voltage on the body surface, coronary sinus and left ventricle leads, requires a delivered charge of 0.04±0.02, 0.05±0.025, and 0.06±0.033 µC, respectively, while to induce a one unit change of the Kscore, requires a delivered charge of 0.93±0.73, 0.32±0.29, and 0.33±0.37 µC, respectively. For all body surface and intracardiac leads, both Δ(alternans voltage) and ΔKscore between baseline and R-wave triggered paced beats increases consistently with an increase in the pacing pulse amplitude, pulse width, and vector spacing. Additionally, we show that the proposed method can be used to suppress spontaneously occurring alternans (n=7), in the presence of myocardial ischemia. Suppression of RA by pacing during the absolute refractory period results in a significant reduction in arrhythmia susceptibility, evidenced by a lower Srank score during programmed ventricular stimulation compared with baseline before ischemia. We have developed and evaluated a novel closed-loop method to dynamically modulate RA in a swine model. Our data suggest that suppression of RA directly reduces arrhythmia susceptibility and reinforces the concept that RA plays a critical role in the pathophysiology of arrhythmogenesis.

Accuracy of cardiac ablation catheter guidance by means of a single equivalent moving dipole inverse algorithm to identify sites of origin of cardiac electrical activation.

We have developed a system that could potentially be used to identify the site of origin of ventricular tachycardia (VT) and to guide a catheter to that site to deliver radio-frequency ablation therapy. This system employs the Inverse Solution Guidance Algorithm based upon Single Equivalent Moving Dipole (SEMD) localization method. The system was evaluated in in vivo swine experiments. Arrays consisting of 9 or 16 bipolar epicardial electrodes and an additional mid-myocardial pacing lead were sutured to each ventricle. Focal tachycardia was simulated by applying pacing pulses to each epicardial electrode at multiple pacing rates during breath hold at the end-expiration phase. Surface potentials were recorded from 64 surface electrodes and then analyzed using the SEMD method to localize the position of the pacing electrodes. We found a close correlation between the locations of the pacing electrodes as measured in computational and real spaces. The reproducibility error of the SEMD estimation of electrode location was 0.21 ± 0.07cm. The vectors between every pair of bipolar electrodes were computed in computational and real spaces. At 120bpm, the lengths of the vectors in the computational and real space had a 95% correlation. Computational space vectors were used in catheter guidance simulations which showed that this method could reduce the distance between the real space locations of the emulated catheter tip and the emulated arrhythmia origin site by approximately 72% with each movement. We have demonstrated the feasibility of using our system to guide a catheter to the site of the emulated VT origin.

Design of Cardiac Pacemaker Based on Low Power MCU

In order to improve the accuracy of the pacemaker's parameter adjustment and to avoid the surgical replacement of the pacemaker when the battery is exhausted, this paper designs a novel single-chamber pacemaker circuit based on low-power single-chip microcomputer. The circuit uses digital control to accurately control the amplitude, pulse width and frequency of the pacing pulse. The circuit is also designed with wireless charging function, and wireless communication with the programmer can wirelessly charge the pacemaker and know the charging information in real time. Wireless charging function can reduce the number of times the patient replaces the pacemaker or even completely avoid it.