Leadless Pacing of the Heart Using Induction Technology: A Feasibility Study

Emerging Technologies in Electrophysiology: From Single Chamber to Biventricular Leadless Pacemakers

BACKGROUND

Transvenous pacemakers have been shown to improve quality of life and mortality in patients with bradycardia and cardiac conduction blocks. However, they possess inevitable drawbacks as they have a relatively high incidence of lead and device pocket-related complications. Therefore, leadless pacemakers have emerged as a solution to reduce the complications seen with conventional pacemakers. However, there have been no clinical trials to date comparing transvenous to leadless pacemakers.

SUMMARY

Currently, the Micra TPS or AV device has been approved for commercial use worldwide but is limited to single-chamber pacing with single or dual-chamber sensing. Although the leadless pacemaker, Nanostim, was initially promising, it has been recalled due to concerns of battery failures and is no longer approved in Europe. In addition, the lack of defibrillation capabilities with leadless pacemakers has been a limiting factor; therefore, a leadless pacemaker with the already approved subcutaneous cardioverter-defibrillator system is currently being studied in humans. Moreover, the WiSE-CRT device has been approved in Europe, with the capabilities for leadless cardiac resynchronization therapy (CRT), to provide CRT for patients with unsuitable coronary sinus anatomy. Furthermore, retrieval of leadless pacemakers has been an area of concern; however, clinic data has signaled towards safe extraction of these devices with minimal complications. Key messages: This review will encompass the current literature regarding clinical safety and outcomes of these novel leadless pacemakers and discuss the evolving technologies in the field of cardiac pacing.

Cardiac Implantable Electronic Device Therapy in Heart Failure

The population of patients with heart failure continues to grow, which introduced significant challenges in clinical practice related to the management of cardiac arrhythmia and advanced heart failure syndromes. Device therapy has increasingly become essential in the management of life-threatening arrhythmia and clinical heart failure in this population. This review will discuss the use of cardiac implantable electronic devices in heart failure with primary focus on sudden cardiac death prevention and cardiac resynchronization, including published evidence and evolving technologies.

Long-term outcome of transvenous pacemaker implantation in infants: a retrospective cohort study

AIM

Evaluation of long-term outcome of transvenous pacemaker (PM) implantation in infants.

METHODS AND RESULTS

A retrospective analysis of all transvenous PM implantations in infants <10 kg between September 1997 and October 2001 was made. Indications for PM implantation, age at implantation, and determinants of long-term outcome including cardiac function, PM function, and PM (system) complications were noted. Seven patients underwent transvenous VVI(R) PM implantation. Median age at implantation was 3 days (range: 1 day to 14 months), median weight 3.5 kg (range: 2.3-8.7 kg), and median follow-up 14 years (range: 12.3-16.3 years). Pacemaker indications were congenital complete atrioventricular block (n = 4), long QT syndrome with heart block (n = 2), and post-operative complete atrioventricular block with sinus node dysfunction (n = 1). No procedural complications were noted. Today all patients are alive and symptom free with good PM and cardiac function. Two patients underwent PM generator relocation for imminent skin necrosis and skin traction. Two patients suffered from asymptomatic left subclavian vein occlusion and developed thrombosis on the PM electrode. Three patients were converted to an epicardial PM system, due to atrial perforation after upgrading procedure (n = 1), syncope with need for implantable cardioverter defibrillator implantation (n = 1), and systolic dysfunction with development of dilated cardiomyopathy, which normalized under cardiac resynchronization therapy pacing (n = 1). Two patients needed atrioventricular (AV) valve repair for severe insufficiency. Two patients underwent repositioning of dysfunctional PM leads. In five patients, transvenous leads were removed. Indications were elective lead replacement (n = 1), atrial perforation (n = 1), and switch to an epicardial system (n = 3).

CONCLUSION

Transvenous PM implantation in infants (<10 kg) is associated with a high incidence of vascular occlusion, thrombosis, and severe atrioventricular valve regurgitation during long-term follow-up. We advocate an epicardial approach for PM implantation in small children.

Leadless pacemakers: A new era in cardiac pacing

Cardiac pacemakers are a critical management option for patients with rhythm disorders. Current efforts to develop leadless pacemakers have two primary goals: to reduce lead-associated post-procedural morbidity and to avoid the surgical scar associated with placement. After extensive studies on animal models and technological advancements, these devices are currently under investigation for human use. Herein, we review the evidence from animal studies and the technological advancements that have ushered in the era of use in humans. We also discuss different leadless pacemakers currently under investigation, along with limitations and future developments of this innovative concept.

Pre-Implant Assessment For Optimal LV Lead Placement In CRT: ECG, ECHO, or MRI?

Cardiac resynchronization therapy (CRT) improves cardiac function in many patients with ventricular dyssynchrony. The optimal use of imaging for pre-implantation assessment remains a subject of debate. Here, we review the literature to date on the utility of echocardiography and cardiac MR, as well as conventional ECG, in choosing the best site for LV lead implantation. Prior to the use of imaging for pre-implantation evaluation, LV leads were placed empirically, based on average responses from population-level studies. Subsequently, patient-specific approaches have been used to maximize response. Both echocardiography and cardiac MR allow determination of areas of latest mechanical activation. Some studies have found improved response when pacing is applied at or near the site of latest mechanical activation. Similarly, both echocardiography and cardiac MR provide information about the location of any myocardial scar, which should be avoided when placing the LV lead due to variable conduction and high capture thresholds. Alternative approaches include targeting the region of latest electrical activation via measurement of the QLV interval and methods based on intraoperative hemodynamic measurements. Each of these modalities offers complementary insights into LV lead placement, so future directions include multimodality pre-implantation evaluation, studies of which are ongoing. Emerging technologies such as leadless implantable pacemakers may free implanting electrophysiologists from the constraints of the coronary sinus, making this information more useful and making non-response to CRT increasingly rare.

State of the art of leadless pacing

Despite undisputable benefits, conventional pacemaker therapy is associated with specific complications related to the subcutaneous device and the transvenous leads. Recently, two miniaturized leadless pacemakers, Nanostim™ (St. Jude Medical) and Micra™ (Medtronic), which can be completely implanted inside the right ventricle using steerable delivery systems, entered clinical application. The WiCS™-cardiac resynchronisation therapy (CRT) system (wireless cardiac stimulation for CRT, EBR Systems) delivers leadless left ventricular endocardial stimulation for cardiac resynchronization. In addition to obvious cosmetic benefits, leadless pacing systems may have the potential to overcome some complications of conventional pacing. However, acute and long-term complications still remains to be determined, as well as the feasibility of device explantation years after device placement.

Permanent leadless cardiac pacing: results of the LEADLESS trial

BACKGROUND

Conventional cardiac pacemakers are associated with several potential short- and long-term complications related to either the transvenous lead or subcutaneous pulse generator. We tested the safety and clinical performance of a novel, completely self-contained leadless cardiac pacemaker.

METHODS AND RESULTS

The primary safety end point was freedom from complications at 90 days. Secondary performance end points included implant success rate, implant time, and measures of device performance (pacing/sensing thresholds and rate-responsive performance). The mean age of the patient cohort (n=33) was 77±8 years, and 67% of the patients were male (n=22/33). The most common indication for cardiac pacing was permanent atrial fibrillation with atrioventricular block (n=22, 67%). The implant success rate was 97% (n=32). Five patients (15%) required the use of >1 leadless cardiac pacemaker during the procedure. One patient developed right ventricular perforation and cardiac tamponade during the implant procedure, and eventually died as the result of a stroke. The overall complication-free rate was 94% (31/33). After 3 months of follow-up, the measures of pacing performance (sensing, impedance, and pacing threshold) either improved or were stable within the accepted range.

CONCLUSIONS

In a prospective nonrandomized study, a completely self-contained, single-chamber leadless cardiac pacemaker has shown to be safe and feasible. The absence of a transvenous lead and subcutaneous pulse generator could represent a paradigm shift in cardiac pacing.

CLINICAL TRIAL REGISTRATION URL

http://clinicaltrials.gov. Unique identifier: NCT01700244.

Pacing device therapy in infants and children: a review

The number of pediatric pacemakers implanted is still relatively small. Children requiring pacing therapy have characteristics that are distinct from those of adults, including physical size, somatic growth, and cardiac anomalies. Considering these features, long-term follow-up of pediatric pacemaker implantation is necessary. Selection of appropriate generators, pacing modes, pacing sites, and leads is important. Generally, epicardial leads are commonly used in small infants. On the other hand, the use of endocardial leads in children is increasing worldwide because of their benefits over epicardial leads, such as minimal invasiveness, lower pacing threshold, and longer generator longevity. Endocardial leads are not suitable for patients with intracardiac shunts because of the high risk of systemic thrombosis. Venous occlusion is another significant problem with endocardial leads. With the increase in the number of pacing device implantations, the incidence of infection from such devices is also increasing. Complete device removal is sometimes recommended to treat device infection, but experience in the removal of endocardial leads in children is still scarce. This article gives an overview of pacing therapy in the pediatric population, including discussions on new pacing systems, such as remote monitoring systems, magnetic imaging compliant pacemaker systems, and leadless pacing devices.

Leadless pacing using induction technology: impact of pulse shape and geometric factors on pacing efficiency

AIMS

Leadless pacing can be done by transmitting energy by an alternating magnetic field from a subcutaneous transmitter unit (TU) to an endocardial receiver unit (RU). Safety and energy consumption are key issues that determine the clinical feasibility of this new technique. The aims of the study were (i) to evaluate the stimulation characteristics of the non-rectangular pacing pulses induced by the alternating magnetic field, (ii) to determine the extent and impact of RU movement caused by the beating heart, and (iii) to evaluate the influence of the relative position between TU and RU on pacing efficiency and energy consumption.

METHODS AND RESULTS

In the first step pacing efficiency and energy consumption for predefined positions were determined by bench testing. Subsequently, in a goat at five different ventricular sites (three in the right ventricle, two in the left ventricle) pacing thresholds using non-rectangular induction pulses were compared with conventional pulses. Relative position, defined by parallel distance, radial distance, and angulation between TU and RU, were determined in vivo by X-ray and an inclination angle measurement system. Bench testing showed that by magnetic induction for every alignment between TU and RU appropriate pulses can be produced up to a distance of 100 mm. In the animal experiment pacing thresholds were similar for non-rectangular pulses as compared with conventional pulse shapes. In all five positions with distances between 62 and 102 mm effective pacing was obtained in vivo. Variations in distance, displacement and angle caused by the beating heart did not cause loss of capture. At pacing threshold energy consumptions between 0.28 and 5.36 mJ were measured. Major determinants of energy consumption were distance and pacing threshold.

CONCLUSION

For any given RU position up to a distance of 100 mm reliable pacing using induction can be obtained. In anatomically crucial distances, up to 60 mm energy consumption is within a reasonable range.

Long-term follow-up after steroid-eluting epicardial pacemaker implantation in young children: a single centre experience

AIMS

The purpose of this paper is the retrospective investigation of the clinical outcome and modes of failure leading to reoperation, as well as the report of the long-term results, in a group of young children who underwent epicardial pacemaker implantation.

METHODS AND RESULTS

Between 2000 and 2008, 45 young children underwent epicardial pacemaker implantation at 3.2 +/- 2.5 years of age for congenital (n = 27) or post-operative (n = 18) atrioventricular block. The follow-up time was 5.7 years +/- 5 months (range: 6 months to 7.3 years). Five lead malfunction events (11%) were detected during the follow-up time, three of which were due to ventricular lead fracture. All revisions could be performed without complications, and all revised pacemakers showed stable pacing and sensing parameters during long-term follow-up. The actuarial freedom from reoperation at 6 years was 88.8 +/- 2%. Median epicardial ventricular and atrial pacing thresholds were stable and excellent at the latest follow-up, with means of 1.1 +/- 0.5 V and 0.7 +/- 0.8 V, respectively.

CONCLUSION

In our patient cohort of 45 young children, epicardial pacing was associated with a satisfactory clinical outcome and acceptable long-term results. The major cause of reoperation in our series was lead fracture. Reoperations were performed at a low risk.