Authored by Sudeb Mukherjee*
Abstract
Introduction: His Bundle Pacing (HBP) is devoid of consequences of remodelling induced by Right Ventricular Apical Pacing (RVAP). Septal pacing has also been studied in several studies. Complications of heart failure, chamber dilatation and QRS prolongation are not seen in HBP and less in septal pacing. This study was done to evaluate outcomes of HBP versus Septal pacing versus RVAP in those patients requiring pacing.
Methods:
Total 100 patients with atrio ventricular block with syncope who required pacing were included in this study. 50 patients underwent RVAP, 38 patients septal pacing and 12 patients underwent His bundle pacing. Detail echocardiogram-based parameters were obtained before and post pacing 6 months. All data collected appropriately and analysed accordingly using SPSS software by 1-way ANOVA with the use of the Holm-Sidak method for pairwise multiple comparisons or by the χ2 test, as appropriate. The statistical test of main treatment effect was an adjusted F test with Kenward-Roger type adjustment of denominator degrees of freedom.Results: HBP was associated with improvements in Left Ventricular Ejection Fraction (LVEF) and other chamber dimension which was statistically significant. Septal pacing was found to be better (not statistically significant although numerically better) compared to RVAP group which showed deterioration of LVEF, chamber dimension and QRS duration.
Conclusion: HBP was found to be more physiological than septal and RVAP group although technically challenging and required expertise.
Keywords: His Bundle Pacing (HBP); Septal pacing; Right Ventricular Apical Pacing RVAP); Left Ventricular Ejection Fraction (LVEF)
Introduction
The cardiac conduction system is a collection of nodes and specialised conduction cells that initiate and co-ordinate contraction of the heart muscle. It consists of sinoatrial (SA) node, atrioventricular (AV) node, atrioventricular bundle (bundle of His) amd purkinje fibres. The sequence of electrical events during one full contraction of the heart muscle starts from SA node spreads across the atria to the AV node, into the bundle of His, down the interventricular septum and via the Purkinje fibres spread along the ventricles, causing them to contract. This rapid conduction allows coordinated ventricular contraction (ventricular systole) and blood is moved from the right and left ventricles to the pulmonary artery and aorta respectively [1-3]. Since the era of Hippocrates (460-375BC) physicians were aware of syncope. Innovative works by different scientists at different times enriched the history of pacemakers gradually. It started from McWilliam [4] to Lidwell (who developed first external pacemaker) [5] to Hyman’s device (used DC current through a bipolar needle electrode) and finally to Zoll [6] who modernized the concept of pacing radically. Over the time through the hand of Earl E. Bakken the first battery-operated wearable pacemaker came into availability later that year for the treatment of heart bloc [7-9]. Microprocessor-driven pacemakers appeared in around 1990. These became very complex devices capable of detecting and storing events utilising several algorithms. The rate-response pattern also adjusted itself automatically to the patient’s activity level.
From the first human implantation the right ventricular (RV) apical pacing has saved millions of lives, but within one decade it was proved to be non-physiological as several deleterious hemodynamic effects were noted during follow up [10]. Chronic RVAP causes left ventricular dilatation and reduction of left ventricular ejection fraction [11]. During RVAP the conduction of the electrical wave front propagates through the myocardium, rather than through the His-Purkinje conduction system as a result the electrical wave form propagates more slowly and induces heterogeneity in electrical activation of myocardium comparable to left bundle branch block [12]. Left ventricular diminished dp/dt changes (pressure changes) has also been found with chronic RVAP [13]. Decrease in contractile sate of LV myocardium leading to LV systolic dysfunction has also been noted in several studies. Subcellular anatomical changes have also been demonstrated in several previous studies that includes various histopathologic abnormalities in paced patients. Histopathological alterations in biopsy samples following pacing include myofiber variation, fibrosis, fat deposition, sclerosis, and mitochondrial morphological changes [14]. Unfavourable effects of right ventricular (RV) pacing include ventricular remodelling, dilation, elevated diastolic filling pressure, increased functional mitral regurgitation, myocardial perfusion defects, and reduced LV ejection fraction. Of all ventricular sites, the RV apex seems to be the most hemodynamically unfavourable [15]. Right ventricular apical pacing (RVAP) has been shown to increase morbidity and mortality in patients receiving a high percentage of cumulative pacing [16]. All these factors lead to search for alternative pacing site. Various alternative pacing sites has been explored that includes Right Ventricular Outflow Tract pacing, Septal Pacing, Biventricular Pacing, Atrial Pacing, Dual Pacing and His Bundle pacing.
Septal pacing
The idea of septal pacing is based on the fact that the septal region of the RVOT and mid RV are the first zones of the ventricle to depolarise, suggesting that pacing from these areas on the right side of the septum would achieve as normal a contraction pattern as possible.
Evolution of his bundle pacing
The term ‘physiological’ was used in Canadian Trial of Physiological pacing (CTOPP) to reflect the terminology at the time of development of the trial [17]. However atrial pacing was considered physiological at that time. Later it was thought that pacing the atrium and ventricle sequentially may solve the problem of unsynchronised contraction and prevent atrial bradycardia but the ventricular activation sequence is clearly not physiological. Studies using biventricular pacing have suggested improvement in patients of left bundle branch block. The dual chamber and VVI implantable defibrillator (DAVID study) randomised patients receiving implantable defibrillators (ICD) either to backup pacing at the rate of 40 bpm or to DDDR pacing at the at the rate of 70 per minutes. The composite end point of death or hospitalisation with heart failure was greater in the group receiving DDDR pacing than in the back up pacing group [18]. There was a very similar benefit with regard to reduction of atrial fibrillation and a significant but weak benefit with regard to hospitalisation for heart failure. Two probable solutions to this problem are: first involves manipulation of pacing modes and timing cycle operation among patients with reliable atrio-ventricular conduction to minimise unnecessary ventricular pacing and preserve normal ventricular conduction and the second involves pacing at alternative ventricular site to attenuate the adverse effects imposed by ventricular desynchronization when ventricular pacing can’t be avoided.
The main purpose of permanent cardiac electrostimulation is to maintain an adequate cardiac rhythm, trying to restore the physiology of the normal excito-conductive physiology of the heart as much as possible. Up until now, importance had been given to two elements that were considered fundamental for physiological pacing: maintenance of the atrioventricular Sequence and the rateresponsive function. If the aim is to mimic physiological activation patterns, the HBP may provide the ideal site. During the last several years there was much work done in the field of DHBP, to extend the indications and to improve the technique. Here in this study the comparative analysis among RVAP, His Bundle Pacing and Septal pacing has been done.
Objective
To find out outcomes of different parameters in 3 different types of pacing, His bundle vs Septal vs RV Apical in selected group of patients. This was a short term follow up study with detail analysis in respect of various parameters mentioned below.
1. To look for ECG QRS duration shortening.
2. To look for Left ventricular Ejection Fraction (LVEF) immediately, after 1 month and after 6 months.
3. To look for Left ventricular Internal Diameter (LVIDD) change at 1 month and at 6 months.
4. To look for Tricuspid Regurgitation (TR) in different group of pacing.
5. To assess biochemical parameters in different groups following pacing.
LV dimensions were measured from the parasternal long-axis M-mode and expressed as Z scores with the use of weight-related normal limits. LV shortening fraction was calculated.
LV volumes were measured from the apical 4- and 2-chamber views with the Simpson biplane method. LV ejection fraction (EF) was calculated and graded as follows: normal
(LV EF ≥55%), subnormal (LV EF <55%), and significantly decreased (LV EF <45%)
Methods
All patients with atrio ventricular block presented/admitted to IPGME&R Hospital in the department of cardiology were included in this study. It was an prospective observational study for total patients of, who were followed for 6 months and all details parameters were documented and analysed accordingly.
Inclusion criterias
For HBP: Only patients who met the following inclusion criteria were considered candidates for permanent HBP:
a) Indication of permanent pacing for AV conduction disturbance or left ventricular resynchronization not possible via the coronary sinus.
b) Potential for elimination of AV block or bundle-branch block by HBP, leading to a narrow QRS complex (120 ms).
c) Maximum hisian capture threshold of 2.5 V/1 ms.
d) 1:1 His-ventricular conduction at a minimum pacing rate of 120 b.p.m.
d) 1:1 His-ventricular conduction at a minimum pacing rate of 120 b.p.m.
B. Potential for elimination of AV block or bundle-branch block (LBBB) by HBP, leading to a narrow QRS complex (120 ms).
For RVAP pacing: For all other patients needed pacing included in this category.
Exclusion criterias
For HBP and Septal Pacing:
1. Complete Heart Block.
2. Wide Complex Tachycardia during any episode before and after admission.
Parameters used
Echocardiographic criterias: 1)Left Ventricular Internal Dimension in Systole and Diastole (LVIDs, LVIDd), 2)Left Ventricular Posterior Wall Thickness (LVPWD), 3)Left Ventricular Ejection Fraction (LVEF), 4) Left Atrial Diameter 5) Right Atrial Diameter 6) Right Ventricular Diameter 7) Tricuspid Regurgitation (TR).
Electrocardiographic criterias: QRS duration, QRS morphology.
Blood investigations: N-Terminal pro Brain Natriuric Peptide.
Study technique: Patients of all ages are going to be included in this study. So, after taking a valid consent from the patients, a detailed history and clinical examination was carried out.
HBP: Procedure HBP was performed using the Medtronic pacing lead delivered through a fixed curve sheath. The delivery sheath was inserted into the right ventricle beyond the tricuspid annulus over a guide wire through left cephalic or axillary vein. Subsequently, the pacing lead was advanced through the sheath such that only the distal electrode /screw is beyond the tip of the catheter. A unipolar electrogram was recorded from the lead tip at again setting of 0.05mV/ mm and displayed on a Medtronic pacing system. The preformed double curve of this catheter points the tip toward the superior AV septum. An HB electrogram was identified by mapping the AV septum. The lead was then screwed in this position by means of 4–5 clockwise rotations. The HB capture threshold was assessed and accepted if found to be 2.5 V at 1.0 ms. If an acceptable HB capture could not be achieved after 5 attempts at lead positioning or a fluoroscopy duration of 30 minutes ,the lead was then placed in the RV mid-septum.
RVAP: RV leads were implanted in a standard fashion at the RV apex . Traditional tined-tip pacing to anchor a lead in the RV apex in those group of patients.
Septum: Septal pacing was done by the methods as described by Mond et, al. Under fluoroscopic imaging in the right anterior oblique view of 30 degrees, the RV was divided into 3 zones as follows: (1) an upper zone (one-third from the top of the RV) between the pulmonary artery bulge and the roof of the tricuspid valve; (2) a middle zone; and (3) a lower zone (one-third from the bottom of the RV). Then, the ventricular lead was anchored in the middle zone of the RV. After fixation of the ventricular lead, the left anterior oblique view of 45 degrees was used to confirm that the lead was successfully placed on the RV septum and not the free wall. Surface and device electrocardiography, and echocardiograpic examination studies were done by be performed at 24 hours after pacemaker implantation using a Vivid 7 Dimension ultrasound machine (GE Healthcare) with an M4S probe and again at 6 months. Echocardiographic parameters were recorded immediately after 1 months and after imlantaton and again at 6 months.
Analysis of data
All data collected appropriately and analysed accordingly. SPSS software latest version was used for demographic as well as objective analysis. ANOVA was done and analysed properly. Continuous data are presented as raw means (SDs). Differences in demographic and informative variables between pacing sites were evaluated by 1-way ANOVA with the use of the Holm-Sidak method for pairwise multiple comparisons or by the χ2 test, as appropriate. The continuous outcome variables characterizing LV function and synchrony were analysed with the use of a linear mixed model approach. Each model included the set of clinically informative additive covariates in addition to the main factor tested. The continuous covariates included age at implantation pacing duration, and QRS duration. The statistical test of main treatment effect was an adjusted F test with Kenward-Roger type adjustment of denominator degrees of freedom.
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