Is right ventricular outflow tract pacing an alternative to left ventricular/biventricular pacing?

Innovations in Cardiac Implantable Electronic Devices

Cardiac implantable electronic devices (CIEDs) are essential for the management of a variety of cardiac conditions, including tachyarrhythmias, bradyarrhythmias, and medically refractory heart failure (HF). Recent advancements in CIED technology have led to innovative solutions that overcome shortcomings associated with traditional devices or address unmet needs. Leadless pacemakers, subcutaneous implantable cardioverter defibrillators (ICDs), and extravascular ICDs eliminate lead-related complications common with conventional pacemakers or ICDs. Conduction system pacing (His bundle pacing and left bundle branch pacing) is a more physiologic method of pacing and avoids the deleterious consequences associated with long-term right ventricular pacing. For HF-related devices, cardiac contractility modulation is an emerging therapy that bridges a gap for many patients ineligible for cardiac resynchronization therapy and has been shown to improve HF symptoms and decrease hospitalizations and mortality in select patients. Implantable pulmonary artery pressure monitors help guide HF management and reduce hospitalizations. Lastly, new phrenic nerve stimulating devices are being utilized to treat central sleep apnea, a common comorbidity associated with HF. While further long-term studies are still underway for many of these new technologies, it is anticipated that these devices will become indispensable therapeutics in the expanding cardiovascular armamentarium.

Right ventricular apical lead position is associated with prolonged signal-averaged P-wave duration

AIM

The study aimed to determine if right ventricular apical pacing is associated with adverse change in atrial substrate compared with right ventricular septal pacing.

METHODS

Patients with septal leads and dual-chamber devices with more than 3 months of follow-up and 70% or higher cumulative percentage of ventricular pacing were compared with a matched group of apically implanted leads with a cumulative percentage ventricular pacing of 70% or higher. Device parameters were recorded, and high-resolution recordings were obtained for signal-averaged P-wave (SAPW) analysis. Previously obtained SAPW recordings taken from 49 healthy patients and 73 patients with paroxysmal atrial fibrillation were used as negative and positive controls, respectively.

RESULTS

Ten patients with septal leads (mean age, 71.9 +/- 12.1 years; mean months implanted, 10.5 +/- 3.2 months) and 9 patients with apical leads (mean age, 71.9 +/- 5.7 years; mean months implanted, 11.4 +/- 6.4 months) were enrolled. The SAPW duration was longer in the apical cohort compared with the septal cohort (144.8 +/- 6.9 and 133.0 +/- 5.5 milliseconds, respectively; P = .001), whereas there was no significant difference between septal and normal cohorts (133.0 +/- 5.5 and 129.3 +/- 7.1 milliseconds, respectively; P = .08).

CONCLUSIONS

Apical pacing is associated with prolonged P-wave duration relative to septal pacing and controls: this may manifest as increased risk of atrial tachycardias and presents a potentially novel benefit of septal pacing.

High-Septal Pacing Reduces Ventricular Electrical Remodeling and Proarrhythmia in Chronic Atrioventricular Block Dogs

OBJECTIVES

This study was designed to analyze the relevance of ventricular activation patterns for ventricular electrical remodeling after atrioventricular (AV) block in dogs.

BACKGROUND

Bradycardia is thought to be the main contributor to ventricular electrical remodeling after complete AV block. However, an altered ventricular activation pattern or AV dyssynchrony may also contribute.

METHODS

For 4 weeks, AV block dogs were either paced from the high-ventricular septum near the His bundle at lowest captured rate (n = 9, high-septal pacing [HSP]) or kept at idioventricular rate without controlled activation (n = 14, chronic AV block [CAVB]). Multiple electrocardiographic and electrophysiological parameters were measured under anesthesia at 0 and 4 weeks. Proarrhythmia was tested at 4 weeks by I(Kr) block (25 mug/kg dofetilide intravenous).

RESULTS

At 0 weeks, the 2 groups were comparable, whereas after 4 weeks of similar bradycardia, QT duration at unpaced conditions had increased from 300 +/- 5 to 395 +/- 18 ms in CAVB (+32 +/- 6%) and from 307 +/- 8 ms to 357 +/- 11 ms in HSP (+17 +/- 4%; p < 0.05). Frequency dependency of repolarization was less steep in HSP compared to CAVB dogs after 4 weeks remodeling. Beat-to-beat variability of repolarization, a proarrhythmic parameter, increased only in CAVB from 0 to 4 weeks. Torsades de pointes arrhythmias were induced at 4 weeks in 44% HSP versus 78% CAVB dogs (p = 0.17). Cumulative duration of arrhythmias per inducible dog was 87 +/- 36 s in CAVB and 30 +/- 21 s in HSP (p < 0.05).

CONCLUSIONS

High-septal pacing reduces the magnitude of ventricular electrical remodeling and proarrhythmia in AV block dogs, suggesting a larger role for altered ventricular activation pattern in the generation of ventricular electrical remodeling than previously assumed.

Right ventricular outflow tract pacing: practical and beneficial. A 9-year experience of 460 consecutive implants

BACKGROUND

Pacing from the right ventricular apex (RVA) in patients with ventricular dysfunction has been identified as a possible contributor to deterioration of ventricular function. Therefore, alternative pacing sites such as the right ventricular outflow tract (RVOT) are receiving intensified scrutiny. An unresolved question is whether technical, procedural, and stability issues are comparable for the RVA and the RVOT.

METHODS

This report details 460 consecutive ventricular pacing lead implants with the primary intended site in the RVOT. Patients were evaluated for success, complication rates, and followed-up for stability of pacing parameters. The total patient implant population included 300 male and 170 female patients with a mean age of 70.6 years. Ten patients were excluded from the analysis, since there was a primary indication and intention to implant in the RVA, leaving a total of 460 patients for analysis. The indications for pacing were symptomatic bradycardia due to any cause and/or Mobitz II or complete heart block. There was no clinical evidence of heart failure in 420 patients. In 40 patients with heart failure, the indication for pacing was cardiac resynchronization therapy using the RVOT as an alternate site when pacing from a branch vein of the coronary sinus was not possible. Outcome information was obtained from the implanter's clinic.

RESULTS

The overall success rate in the RVOT was 84% over the total 9-year period with a 92% success rate in the last 4(1/2) years, using the RVOT technique described. At 20 months in a subgroup comparison of RVOT and RVA implants, there was no significant difference in pacing threshold, R-wave sensing, or pacing lead impedance. Dislodgment occurred in only 1 of 460 patients. Reasons for failure to implant in the RVOT include inability to find a stable position with adequate pacing and sensing thresholds (related to anatomy, scarred myocardium, pulmonary hypertension, tricuspid regurgitation), hemodynamic instability limiting time for implant, and a learning curve. Long-term stability and lead performance were excellent, and certain acute and chronic complications of RV pacing did not occur.

Pediatric cardiac resynchronization pacing therapy

PURPOSE OF REVIEW

Advances in pacemaker lead designs, permitting precise lead implantation at sites other than the ventricular apex, have provoked interest in the utilization of ventricular pacing beyond maintenance of heart rate. Select older adult patients with various cardiomyopathies may improve clinically following alternative site, biventricular and cardiac resynchronization pacing. This report reviews recent applications and directions of these pacing technologies to younger patients with congenital heart defects.

RECENT FINDINGS

Acutely, following congenital heart surgery or chronically, studies now indicate that select younger patients may demonstrate physiologic benefits from pacing preselected single ventricular or combined right and left ventricular sites. This may prevent eventual paced myocardial deterioration as well as support and even reverse existing myocardial dysfunction, deferring the need for heart transplantation.

SUMMARY

There are limited worldwide pediatric experiences, and, to date, no randomized multicenter studies. It is becoming more evident, however, that as these pacing techniques are used in younger patients, clinical improvements, comparable to older adult patients, even delaying heart transplant, may be anticipated. Since these newer techniques are more complicated and costly than simple pacemaker implantation, future directions will be for multi-institutional pediatric studies with clear definition of which pre-implant variables will define physiologic improvement.

Cardiac resynchronisation therapy for heart failure

Heart failure (HF) is increasingly common and, despite advances in pharmacotherapeutic management, often progresses. Progression is marked by structural and electrical changes-remodelling. In approximately one-third of patients, ventricular dilatation is accompanied by intraventricular conduction delays, most commonly the left bundle branch block (LBBB). The presence of LBBB is associated with mechanical dyssynchrony of the heart. Cardiac resynchronisation therapy (CRT), the use of special pacemakers with or without implantable cardioverter defibrillators, aims to resynchronise the failing heart, improving myocardial contraction without increased energetics. Several, large, randomised clinical trials have now established the benefit of CRT in a select group of HF patients, providing functional and, recently shown, mortality benefits. However, a substantial proportion of patients are considered non-responders to CRT, and studies are now underway to identify the patients most likely to respond to CRT.

Temas de actualidad en estimulación cardíaca 2005

Currently, three areas of active development in cardiac pacing are of particular interest to clinical cardiologists. Biventricular pacing is now considered a type-I indication for adjuvant treatment in advanced and refractory heart failure. Consequently, some changes in everyday clinical practice will be seen when patients with end-stage heart failure start to receive resynchronization therapy. Secondly, the Cardiac Pacing Working Group of the Spanish Society of Cardiology has developed a national consensus document on sleep apnea and cardiac rhythm abnormalities. It appears that a novel way of tackling the current growing epidemic could be to use permanent cardiac pacing in an attempt to modify the cardiac rhythm alterations, mainly bradyarrhythmias, related to sleep apnea. Finally, promising developments are taking place in systems designed to reduce the unwanted right ventricular stimulation sometimes observed with antibradycardia pacing modalities. These new systems are expected to minimize significantly the well-known deleterious hemodynamic effects sometimes seen in our patients.

Progress in Cardiovascular Disease: Technical Considerations in Cardiac Resynchronization Therapy

Cardiac resynchronization therapy (CRT) has been shown to improve symptoms, ventricular function, and survival in patients with left ventricular systolic dysfunction and ventricular conduction delay. Patients with moderate to severe drug-refractory heart failure symptoms along with ventricular dyssynchrony, manifested as prolongation of the QRS duration on the surface electrocardiogram, benefit from CRT. Owing to the growing awareness and application of CRT, a large number of patients have been identified as candidates for this therapy, making it necessary for clinicians involved in the care of such patients to be adequately knowledgeable of various aspects of CRT implementation. In particular, clinicians involved in the care of these patients must be aware of the practical considerations in preparing patients for the implantation procedure, careful surveillance for early or late procedure-related complications, and knowledge of the fundamental device features so as to tailor therapeutic and programming techniques to improve long-term response to CRT. This review addresses the technical considerations of the implantation procedure and device function with emphasis on the initial and long-term programming to ensure optimal delivery of CRT.

Benefits, unresolved questions, and technical issues of cardiac resynchronization therapy for heart failure

This review aims to provide a synthesis of the published evidence regarding the rationale and clinical benefits of cardiac resynchronization therapy (CRT) with implantable atrial-synchronized biventricular pacing (BVP) devices in patients with moderate to advanced heart failure and intra- and interventricular conduction delays. In addition, it addresses clinical and technical issues that have yet to be resolved, such as the selection of the most suitable candidates for CRT; the usefulness of combining BVP with automatic defibrillation backup; the value of CRT in patients with atrial fibrillation; the importance of alternative sites of pacing, such as the atrial septum and the right ventricular (RV) outflow tract; the harmful effects of the long-standing practice of producing an iatrogenic left bundle branch block by conventional RV pacing in patients receiving standard permanent pacemakers; the question of precisely where on the left ventricle optimal pacing is achieved; and the potential applications of CRT in patients with pediatric or congenital heart disease. Considering how major advances have been achieved since the first clinical application of CRT in 1994, one can be optimistic about the future of the electrotherapeutic management of heart failure.

Controversies in pacing: Indications and programming

This article reviews controversies in cardiac pacing in four areas: methods to prevent unnecessary right ventricular pacing and optimal ventricular pacing sites in the bradycardia population, pacing for prevention of atrial fibrillation (AF), a novel pacing technique for the treatment of heart failure, and pacing for the treatment of sleep apnea. Frequent right ventricular pacing has been reported to increase the incidence of AF and congestive heart failure. However, many patients with pacemakers for bradycardia have intrinsic atrioventricular conduction most of the time. Optimal programming of pacemakers and new algorithms designed to reduce unnecessary ventricular pacing are discussed. Pacing algorithms for prevention of AF have generally been shown to be ineffective. Atrial antitachycardia pacing has been shown to reduce the burden of atrial tachyarrhythmias in selected patients. Cardiac contractility modulation has recently been reported to be a promising new approach to the treatment of heart failure. Some pacing techniques may be effective in the treatment of sleep apnea but larger, long-term clinical trials are required to demonstrate a significant clinical benefit.