Effects of Internal Defibrillation on an Implanted Pacing System with Programmable Polarity

Management of multiple cardiac arrhythmias in some patients with both an implantable cardioverter defibrillator (ICD) and a pacemaker has demonstrated several advantages. In such circumstances, it is imperative that pacemaker function and its programmed parameters be preserved following a deftbrillation shock. This article describes the effects encountered by a specific programmable polarity pacemaker (Relay® 294–03) when subjected to electrical defibrillation in a canine model. Three pacemakers were repeatedly tested in three separate dog experiments. Each pacemaker, with its leads implanted in the right atrium and the right ventricle, was subjected to a minimum total number of 24 high energy biphasic and monophasic shocks (600–700 V) delivered by a coexisting ICD system using three different defibrillating lead configurations. None of the pacemaker systems showed any failure in function; all pacemakers continued to function within preshock specification and conversion to unipolar pacing and/ or backup mode was not observed in any of the tests. Intracardiac electrical potentials measured directly off the ICD and the pacemaker leads, during a defibrillation shock (mean 566.6 V; 23.7 J), showed that potentials measured in a bipolar configuration (tip-ring: mean 21.0 V in atrium, 12.0 V in ventricle) were significantly less than potentials measured in a unipolar configuration (tip-can: mean 387.9 V in atrium, 394.0 V in ventricle; ring-can: mean 405.6 V in atrium, 395.4 V in ventricle). Our compatibility tests demonstrate that use of this programmable-polarity pacemaker in concert with an ICD system appears to be safe. Testing similar to the present study should be conducted prior to complete clinical acceptance of combined ICD and pacemaker implantation.     

Treatment of superior vena cava obstruction secondary to pacemaker wires with balloon venoplasty and insertion of metallic stents.

AIMS: Pacemaker wires can result in stenosis of the superior vena cava and other central veins. The aim of this study is to demonstrate the safety and effectiveness of treating stenoses of the superior vena cava (SVC) and central veins with balloon venoplasty and metallic stent insertion in the presence of cardiac pacemaker wires. METHODS AND RESULTS: Three patients were referred to the department after developing symptomatic SVC obstruction following implantation of a cardiac pacemaker several years earlier. They were examined with duplex ultrasound and venography, which revealed significant stenoses of the central veins. These patients subsequently underwent endovascular treatment which involved balloon dilation and stent insertion. The treatment was successful in all three patients, without any complications. Long-term patency of up to 4 years is recorded. No pacemaker function dysfunction was encountered. CONCLUSION: SVC stenting is safe and effective in patients who develop the SVC obstruction after cardiac pacemaker insertion.     

Necrotizing vasculitis: a cause of aortic insufficiency and conduction system disturbance

Cardiac involvement in vasculitis syndromes is uncommon. We describe a 50-year-old male who presented with progressive dyspnea and myalgies. Echocardiogram revealed significant thickening of aortic root, aortic cusps, and anterior mitral valve leaflet, with severe aortic regurgitation that required aortic valve replacement. Furthermore, this patient suffered progressive atrioventricular block that needed implantation of a pacemaker. The study performed disclosed the presence of necrotizing vasculitis positive for perinuclear antineutrophil cytoplasmic antibody.     

Safety considerations for magnetic resonance imaging of pacemaker and ICD patients

Summary Magnetic resonance imaging (MRI) has evolved as an important diagnostic tool in medicine. However, due to safety concerns the presence of an implanted cardiac pacemaker is considered to be a contraindication to MRI in most medical centers. Previous in vitro and in vivo studies showed that strong electromagnetic fields in the MRI environment may cause asynchronous pacing, inhibition of a demand pacemaker, induced currents in the pacemaker system and pacing of the heart, or potential risk of thermal myocardial injury around the pacing lead tip. ICDs in addition are not able to charge and apply a therapy in the strong magnetic field. There are reported lethal consequences of MRI in patients with pacemakers. However, there are also recent reports of small series of pacemaker patients who have safely undergone MRI. At present time, non-MRI modalities should be considered, whenever possible, to make a diagnosis in pacemaker recipients. If other imaging modalities are not adequate, MRI at low field strengths (0.5 Tesla or less) with careful monitoring and preparation for adverse events may be considered only in experienced centers. The device should be programmed to an asynchronous, or if possible to a non-pacing mode, during MRI. Pacemaker mode changes, inappropriate pacing behavior due to induced voltages, and localized heating at the lead tip are the primary issues that remain to be fully investigated in future studies.This work is supported by a grant from the Bakken Research Center, Medtronic Inc., Maastricht, the Netherlands.     

永久性心脏起搏器植入早期左心室重构的研究

目的分析起搏器植入后早期左心室重构特点.方法全组患者27例,其中,起搏心室感知心室R波抑制型(VVI)起搏器组15例,起搏双腔感知双腔P波/R波抑制型(DDD)起搏器组12例.采用双探头门控单光子发射计算机断层摄影系统(GSPECT)采集心肌显像资料,测定患者起搏器植入前及植入后随访时(随访期4.6±1.5个月)自身心律状态时下列左心室参数值:左心室射血分数(LVEF),左心室舒张末容积(EDV),左心室收缩末容积(ESV).EDV增加或降低10%及以上者,为重构.结果13例(48.1%)出现重构,VVI组10例(66.7%),DDD组3例(25%).其中,EDV增大7例(25.9%),VVI组5例(33.3%),DDD组2例(16.7%);EDV减少者6例(22.2%),VVI组5例(33.3%),DDD组1例(8.3%).结论起搏器植入后早期,即可出现左心室重构,表现在EDV增大或缩小.本研究提示,永久性心脏起搏器植入在获得电生理学益处的同时,可能对左心室结构带来某些不利影响.     

Electrocardiographic evidence of ischemia during ventricular paced rhythms

Exercise-induced electrocardiographic (ECG) changes are the most widely recognized noninvasive means for detecting myocardial ischemia. The specificity of these changes depends on the normalcy of the resting ECG. Right ventricular pacing produces major QRS and ST-T changes very similar to those of complete left bundle-branch block. They alter the resting ECG such that ischemic changes are considerably difficult to detect. Because of these resting abnormalities, ECG changes during treadmill exercise testing usually do not facilitate the diagnosis of ischemia or coronary artery disease. The following are two cases of ischemic ECG changes that occurred during right ventricular pacing. To our knowledge, there have been no reports of the classic ECG changes of ST-segment depression suggestive of ischemia which occurred during right ventricular pacing and which were discemible from the resting ECG changes.     

Conscious Sedation Versus General Anesthesia in Transcatheter Aortic Valve Replacement: The German Aortic Valve Registry

Objectives

The aims of this study were to report on the use of local anesthesia or conscious sedation (LACS) and general anesthesia in transcatheter aortic valve replacement and to analyze the impact on outcome.

单根电极导管VDD起搏系统的临床应用和随访

对１３例窦房结功能正常的高度房室传导阻滞患者植入单根电极导管ＶＤＤ起搏系统，并进行随访观察。结果显示：术中所测Ａ波平均振幅为２．４±１．４ｍＶ；随访期间（平均１１±４．９个月）Ａ波感知阈值无显著性变化（Ｐ＞０．０５），房室同步起搏率保持在１００％，无心房感知不良、肌电干扰和起搏器介导性心动过速等并发症。表明单电极导管ＶＤＤ起搏系统具有植入简便和房室同步功能稳定的特点，是高度房室传导阻滞伴窦房结功能正常者的理想治疗方法。     

Hyperpolarization-activated Cyclic nucleotide-gated Channel and Cardiac Biological Pacemaker:Part Ⅰ

Hyperpolarization-activated cyclic-nucleotide-gated (HCN) channels in the heart modulate cardiac automaticity via the hyperpolarization-activated cation current ( named Ⅰf, Ⅰh, or Ⅰq). Recent studies have unveiled the molecular identity of HCN (HCN1-4) channels. HCN isoforms are unevenly expressed in the heart, even in the sinoatrial node. Features of HCN currents have been characterized in cardiac and other types of cells or in cell lines transfected with the HCN isoforms. The factors modulating Ih and the physiological significance of HCN channels in the heart have been extensively investigated in recent years. The hypothesis for transplanting and/or creating biological pacemakers to replace diseased sinoatrial and/or atrioventricular nodes has been postulated and tested in animal models. Local overexpression of HCN2 channels in the left atrium or in the left conductive bundle branch of the left ventricle via gene delivery induced significant Ⅰh and escape rhythms during vagal stimulation in canines. In addition, implantation of human mesenchymal stem cells with overexpression of HCN2 channels to the canine left ventricular wall was associated with formation of spontaneous escape rhythms of left-sided origin during vagal-stimulation-induced sinus arrest. This preliminary data suggest that the use of HCN channels may hold great promise in,the development of biological pacemakers.