Result of the Physiologic Pacing Registry, an international multicenter prospective observational study of conduction system pacing

BACKGROUND

Conduction system pacing (CSP), including both left bundle branch area pacing (LBBAP) and His-bundle pacing (HBP) has been proposed as an alternative therapy option for patients with indication for cardiac pacing to treat bradycardia or heart failure.

OBJECTIVE

The purpose of this study was to evaluate implant success, safety, and electrical performances of HBP and LBBAP in the multinational Physiological Pacing Registry.

METHODS

The international prospective observational registry included 44 sites from 16 countries globally between November 2018 and May 2021.

RESULTS

Of 870 subjects enrolled, CSP lead implantation was attempted in 849 patients. Subjects with successful CSP lead implantation were followed for 6 months (5 ± 2 months). CSP lead implantation was successful in 768 patients (90.4%). Implant success was 95.2% (239/251) for LBBAP and 88.5% (529/598) for HBP (P = .002). Procedural duration and fluoroscopy duration were comparable between LBBAP and HBP (P = .537). Capture threshold at implant was 0.69 ± 0.39 V at 0.46 ± 0.15 ms in LBBAP and 1.44 ± 1.03 V at 0.71 ± 0.33 ms in HBP (P <.001). Capture threshold at 6 months was 0.79 ± 0.33 V at 0.44 ± 0.13 ms in LBBAP and 1.59 ± 0.97 V at 0.67 ± 0.31 ms in HBP (P <.001). Pacing threshold rise ≥1 V was observed at 6 months in 3 of 208 (1.4%) of LBBAP and 55 of 418 (13.2%) of HBP (P <.001). Serious adverse events related to implant procedure or CSP lead occurred in 5 of 251 (2.0%) with LBBAP and 25 of 598 (4.2%) with HBP (P = .115).

CONCLUSION

This large prospective multicenter study demonstrates that CSP is technically feasible in most patients with relatively higher implant success and suggests that, with current technology, LBBAP may have better pacing parameters than HBP.

Improved Outcomes of Conduction System Pacing in Heart Failure with Reduced Ejection Fraction - A Systematic Review and Meta-analysis

Conduction system pacing (CSP) - His bundle pacing (HBP) and Left bundle branch area pacing (LBBAP) - are emerging alternatives to biventricular pacing (BVP) for cardiac resynchronization therapy (CRT) in heart failure. However, evidence is largely limited to small and observational studies. We conducted a meta-analysis including a total of 15 randomized control trials (RCTs) and non-RCTs that compare CSP (HBP & LBBAP) with BVP in patients with CRT indications. We assessed the mean differences in QRS duration (QRSd), pacing threshold, left ventricular ejection fraction (LVEF), and New York Heart Association (NYHA) class score. CSP resulted in a pooled mean QRSd improvement of -20.3 ms (95% CI -26.1 - -14.5, p<0.05, I²=87.1%) versus BVP. For LVEF, a weighted mean increase of 5.2% (95% CI 3.5-6.9, p<0.05, I²=55.6) was observed following CSP versus BVP. The mean NYHA score was reduced by -0.40 (95% CI -0.6 - -0.2, p<0.05, I²=61.7) post-CSP versus BVP. Subgroup analysis of outcomes by LBBAP and HBP demonstrated statistically significant weighted mean improvements from both CSP modalities for QRSd and LVEF compared to BVP. LBBAP resulted in NYHA improvement compared to BVP without differences between CSP subgroups. LBBAP is associated with a significantly lowered mean pacing threshold of -0.51V (95% CI -0.68 - -0.38) whilst HBP had increased the mean threshold (0.62V, 95% CI -0.03 - 1.26) compared to BVP, however, this was associated with significant heterogeneity. Overall, both CSP techniques are feasible and effective CRT alternatives for heart failure. Further RCTs are needed to establish long-term efficacy and safety.

Pacing-induced cardiomyopathy: A systematic review and meta-analysis of definition, prevalence, risk factors, and management

Pacing-induced cardiomyopathy is a potential complication of right ventricular pacing. Definition varies between studies and the optimal management approach is uncertain. We aimed to characterize definition, prevalence, risk factors, and treatment strategies of pacing-induced cardiomyopathy (PiCM). We performed a systematic review and meta-analysis of studies that evaluated PiCM after pacemaker implantation identified through a literature search of PubMed and EMBASE up to March 2022. We collected data on the study definition of PiCM and calculated pooled prevalence across studies. Meta-analysis with random effects modeling was used to assess the association between potential risk factors and PiCM, reported as odds ratio with 95% confidence interval. Twenty-six studies (6 prospective studies) with a total of 57,993 patients (mean/median age range was 51-78 years; female 45%) were included in the final analysis. Fifteen unique definitions of PiCM were reported. The pooled prevalence of PiCM was 12% (95% confidence interval 11%-14%). In meta-analysis, risk factors included male sex, history of myocardial infarction, chronic kidney disease, atrial fibrillation, baseline left ventricular ejection fraction, native QRS duration, right ventricular pacing percentage, and paced QRS duration. Treatment strategies identified included biventricular cardiac resynchronization therapy (6 studies) and His-bundle pacing (3 studies). Definition of PiCM varied significantly between studies. More than 1 in 10 patients with chronic right ventricular pacing developed PiCM. Key risk factors included baseline left ventricular ejection fraction, native QRS duration, RV pacing percentage, and paced QRS duration. The optimal management strategy has yet to be defined. Further research is needed to define and treat this understated complication.

Miniaturized implantable cardiac monitor with a long sensing vector (BIOMONITOR III): Insertion procedure assessment, sensing performance, and home monitoring transmission success

BACKGROUND

Implantable Cardiac Monitors (ICMs) are used for long-term monitoring of arrhythmias. BIOMONITOR III is a novel ICM with a miniaturized profile, long sensing vector due to a flexible antenna, simplified implantation with a dedicated insertion tool for pocket formation and ICM placement in a single step, and daily automatic Home Monitoring (HM) function.

METHODS

In 47 patients undergoing BIOMONITOR III insertion for any ICM indication, 16 investigators at 10 Australian sites assessed handling characteristics of the insertion tool, R-wave amplitudes, noise burden, P-wave visibility, and HM transmission success. Patients were followed for 1 month.

RESULTS

All 47 attempted insertions were successful. Median time from skin incision to removal of the insertion tool after ICM insertion was 39 s (IQR 19-65) and to wound closure and cleaning was 4.7 min (IQR 3.5-7.8). All aspects of the insertion tool were rated as "good" or "excellent" in ≥97.9% and "fair" in ≤2.1% of patients, except for "force needed for tunnelling" (91.5% good/excellent, 8.5% fair). Based on HM data, R-waves in the first month were stable at 0.70 ± 0.37 mV. Median noise burden (disabling automatic rhythm evaluation) was 0.19% (IQR 0.00-0.93), equivalent to 2.7 min (IQR 0.0-13.4) per day. In HM-transmitted ECG strips with regular sinus rhythm, P-waves were visible in 89 ± 24% of heart cycles. Patient-individual automatic Home Monitoring transmission success was 98.0% ± 5.5%.

CONCLUSIONS

The novel ICM performed well in all aspects studied, including fast insertion, reliable R-wave sensing, good P-wave visibility, and highly successful HM transmissions.

BioMonitor 2 Pilot Study: Early Experience With Implantation of the Biotronik BioMonitor 2 Implantable Cardiac Monitor

BACKGROUND

The BioMonitor 2 Pilot Study assessed the implantation procedure, the sensing amplitude and the remote monitoring transmission success rate of the second generation implantable cardiac monitor, the BioMonitor 2 (Biotronik, Berlin, Germany).

METHODS

This was a prospective, multi-centre, single-arm, non-randomised study involving seven operators in five sites across Australia. Data were collected at implantation, during clinic visits at 1 week and 1 month post-implantation, and through wireless remote monitoring.

RESULTS

Thirty patients with indications for long-term cardiac monitoring underwent successful insertion of a study device. The median implantation time was 9 minutes (interquartile range (IQR) 5-14 mins). The mean R-wave amplitude at 1 week was 0.75±0.39mV and remained stable over the follow-up period. Within 1 day, 97% of the patients connected to the remote monitoring network and daily messages were transmitted on 93.8% of all study days. Seventy-six per cent of patients transmitted at least one subcutaneous ECG (sECG), with a median number of sECGs per patient of seven (IQR 3-37) within 28 days.

CONCLUSIONS

The results of the BioMonitor 2 Pilot study confirm the excellent sensing amplitudes afforded by this new device and the utility of the implantation tools and technique. Patient compliance with and the transmission success rate of the home monitoring system were excellent.

Ambulatory electrocardiographic monitoring

This article forms part of our 'Tests and results' series for 2011 which aims to provide information about common tests that general practitioners order regularly. It considers areas such as indications, what to tell the patient, what the test can and cannot tell you, and interpretation of results.

Histopathological and biochemical effects of green tea and/or licorice aqueous extracts on thyroid functions in male albino rats intoxicated with dimethylnitrosamine

Objective

To investigate histopathological and biochemical effects of green tea and/or licorice aqueous extracts in thyroid functions in male albino rats intoxicated with Dimethylnitrosamine.

Methods

40 Male albino rats were divided into two main groups, 20 normal rats and 20 DMN intoxicated rats. Normal rats were subgrouped into 4 equal groups, group A without treatment (controls), group B treated with green tea, group C treated with licorice, group D treated with green tea and licorice. DMN intoxicated rats were subgrouped into 4 equal groups, group E treated with DMN, group F treated with DMN and green tea, group G treated with DMN and licorice, group H treated with DMN, green tea and licorice. The rats were permitted for free access to solubilized extracts of green tea and or licorice for 4 weeks. All rats in groups E, F, G, H were treated by intraperitoneal DMN (4 mg dissolved in 2.5 ml distilled water/kg body weight) seven times every 2 days in the first two weeks. Plasma total triiodothyronine and tetraiodothyronine were determined by radioimmunoassay. Thyroxine 5^-monodeiodinase activity of liver was determined by spectrophotometeric method. Plasma thyroid stimulating hormone was determined by chemiluminometric technique. Histopathological examination was conducted.

Results

Histopathologically thyroid gland of DMN intoxicated rats showed degeneration (DG)and desquamation (DS) of the lining epithelium and atrophy of many acini with hyperemia (H) in the stromal capillaries and In comparison with control, the administration of DMN alone induced decrease in plasma levels of T3 and T4 while it induced increase in plasma levels of TSH and hepatic activity of Thyroxine 5^-monodeiodinase. Coadminstration of DMN and green tea attenuated the lowering effect of DMN on plasma levels of T3 and T4 and induced increase in these levels but values are still below normal ones while Co administration of DMN with licorice or mixture did not affect these levels. Co administration of green tea and/or licorice with DMN attenuated the rising effect of DMN on hepatic activity of Thyroxine 5^--DI while augmented the rising effect of DMN on plasma level of TSH.

Conclusion

Aqueous extract of green tea may be effective in amelioration of biochemical effects and histopathological lesions induced by DMN.

Utility of isoproterenol in unmasking latent escape rhythm in pacemaker dependent patients undergoing pacemaker replacement

Pacemaker generator replacement in dependent patients may be managed with a bridging temporary pacing lead or by replacing the generator very expediently. The 2 options involve a small risk, and temporary pacing introduces additional cost. This study was conducted to explore the utility of a graduated rate-decrease protocol with isoproterenol support in unmasking an intrinsic rhythm that would obviate the 2 strategies. The protocol was used in 100 consecutive pacemaker-dependent patients (mean age 74.4 +/- 13.7 years, 56% men) who underwent permanent pacemaker replacement. Device lower rates were decremented in 1-minute intervals to 60, 50, 40, and 30 beats/min. If no intrinsic rhythm of > or =30 beats/min was observed after 1 minute, isoproterenol was infused at 1 microg/min for 2 minutes, followed by 2 microg/min for 2 minutes. Of the 100 patients, 59 demonstrated intrinsic rhythm during pacing step-down alone. Of the remaining 41 patients, 28 (68.3%) demonstrated intrinsic rhythm during isoproterenol infusion. The escape rhythm was junctional in 29%, idioventricular in 23%, conducted atrial fibrillation in 16%, and sinus in 15%. Only 13 of 100 patients (13%) failed to demonstrate adequate intrinsic rhythm after the protocol. In conclusion, this suggests that a standardized protocol to elicit an underlying rhythm in patients previously assessed as pacemaker dependent effectively minimizes the need for temporary pacing during device replacement.

Molecular and Electrophysiological Bases of Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmogenic disorder characterized by adrenergically mediated polymorphic ventricular tachyarrhythmias. Genetic investigations have identified two variants of the disease: an autosomal dominant form associated with mutations in the gene encoding the cardiac ryanodine receptor (RyR2) and a recessive form associated with homozygous mutations in the gene encoding the cardiac isoform of calsequestrin (CASQ2). Functional characterization of mutations identified in the RyR2 and CASQ2 genes has demonstrated that CPVT are caused by derangements of the control of intracellular calcium. Investigations in a knock-in mouse model have shown that CPVT arrhythmias are initiated by delayed afterdepolarizations and triggered activity. In the present article, we review clinical and molecular understanding of CPVT and discuss the most recent approaches to develop novel therapeutic strategies for the disease.

A Novel Pacing Maneuver to Localize Focal Atrial Tachycardia

BACKGROUND

Although focal atrial tachycardias cannot be entrained, we hypothesized that atrial overdrive pacing (AOP) can be an effective adjunct to localize the focus of these tachycardias at the site where the post-pacing interval (PPI) is closest to the tachycardia cycle length (TCL).

METHODS

Overdrive pacing was performed in nine patients during atrial tachycardia, and in a comparison group of 15 patients during sinus rhythm. Pacing at a rate slightly faster than atrial tachycardia in group 1 and sinus rhythm in group 2 was performed from five standardized sites in the right atrium and coronary sinus. The difference between the PPI and tachycardia or sinus cycle length (SCL) was recorded at each site. The tachycardia focus was then located and ablated in group 1, and the atrial site with earliest activation was mapped in group 2.

RESULTS

In both groups the PPI-TCL at the five pacing sites reflected the distance from the AT focus or sinus node. In group 1, PPI-TCL at the successful ablation site was 11 +/- 8 msec. In group 2, PPI-SCL at the site of earliest atrial activation was 131 +/- 37 msec (P < 0.001 for comparison). In groups 1 and 2, calculated values at the five pacing sites were proportional to the distance from the AT focus or sinus node, respectively.

CONCLUSIONS

The PPI-TCL after-AOP of focal atrial tachycardia has a direct relationship to proximity of the pacing site to the focus, and may be clinically useful in finding a successful ablation site.

Characteristics of Slow Pathway Conduction After Successful AVNRT Ablation

BACKGROUND

AV node slow pathway conduction can persist following successful ablation for AV node reentrant tachycardia (AVNRT). We hypothesized that careful examination of AV nodal conduction curves before and after effective AVNRT ablation in patients with persistent slow pathway conduction could shed light on this apparent paradox.

METHODS AND RESULTS

Thirty patients (age 40.9 +/- 14.3; 8 male) were included. AV node function curves were created based on pre- and postablation atrial extrastimulus testing. Analysis of slow pathway function curves demonstrated significant decrease in AH for any given coupling interval after ablation (mean difference -68.1 [-94.5, -41.7] P < 0.001), graphically indicated by downward displacement of the curve. In addition, mean slow pathway effective refractory period (ERP) increased from 247.9 +/- 36.1 msec to 288.6 +/- 56.0 msec (P < 0.001); mean maximum AH interval decreased from 361.3 +/- 114.2 msec to 306.9 +/- 65.2 msec (P = 0.013); mean difference in minimum and maximum AH interval during slow pathway conduction decreased (from 94.5 +/- 75.8 msec to 59.6 +/- 46.2 msec (P = 0.016). Finally, mean difference between the fast and slow pathway effective refractory periods, the span of coupling intervals over which slow pathway conduction occurred, decreased (from 113.9 +/- 61.4 msec to 63.2 +/- 41.5 msec, P = 0.001).

CONCLUSIONS

Ablation, which successfully eliminates inducible and spontaneous AVNRT in the presence of persistent slow pathway conduction, is associated with significantly altered slow pathway conduction characteristics, indicating the presence of a damaged or different slow pathway after ablation, incapable of sustaining tachycardia.

Long-Term Variations in Optimal Programming of Cardiac Resynchronization Therapy Devices

The optimal follow-up and long-term programming of cardiac resynchronization therapy (CRT) devices are uncertain. The aim of this study was to quantify the temporal variations in programming parameters to optimize the follow-up of these devices. Before, during, and at specified intervals over 9 months after implant, 40 recipients of CRT devices were studied. At each visit, the patients were tested with a fixed sequence of stimulation parameters during echocardiographic and electrocardiographic (ECG) recordings. The optimal AV delay and inter-ventricular delays (V-V) were determined according to echocardiographic criteria. The echocardiographic data were, in turn, compared with the ECG recordings. Among the 40 patients, the optimal stimulation parameters remained unchanged throughout the follow-up in only three patients. In 18 patients, adjustments were required at each follow-up sessions. There was a trend toward reduction in the left ventricular (LV) predominance of the optimal V-V delay and an increase in the AV delay during follow-up. The mean optimal V-V delay at implant was 22 ms (-12 to +32 ms) with the LV activated first, versus 12 ms (-16 to +32 ms) at 9 months. The mean AV delay at implant was 115 ms versus 137 ms at 9 months. Individual changes could not be accurately predicted. The optimal stimulation parameters for CRT vary over time. Detailed, regular reevaluations, and reprogramming of optimal parameters may be appropriate.

Bifocal Right Ventricular Cardiac Resynchronization Therapies in Patients with Unsuccessful Percutaneous Lateral Left Ventricular Venous Access

Biventricular cardiac resynchronization therapy (CRT) with a lateral left ventricular (LV) lead cannot always be achieved. We report a single center experience of CRT utilizing a protocol that specifically required the implantation of a bifocal right ventricular (RV) lead system when lateral LV pacing could not be achieved. Consecutive candidates for CRT were included in the study. If strict criteria for lateral LV pacing were not met, they underwent implantation of a bifocal RV lead system with two 7F, active fixation leads, one placed septally at the apex, and the other in the high septal outflow tract. All patients were followed for 12 months and the two groups were compared. A biventricular (BiV) stimulation system was implanted in 44 patients, and a bifocal RV system in six. The demographic characteristics of the two groups were similar. Both groups experienced a similar improvement in functional capacity, increase in 6 minutes walking distance, and decreased need for hospitalizations. The mean increase in LV ejection fraction was 11% in the bifocal RV group versus 10% in the BiV group. Though the tissue Doppler indices of LV synchrony improved earlier in the BiV group, (19% vs 10%) the improvement was similar in both groups at 6 months (23% vs 20%). The clinical improvements conferred by CRT can be matched by a bifocal RV system in selected patients. This alternate approach should be considered when implantation of a LV lateral lead was unsuccessful.