A Real-world Experience of Atrioventricular Synchronous Pacing with Leadless Ventricular Pacemakers

Aims: The MicraTM transcatheter pacing system (TPS) (Medtronic) is the only leadless pacemaker that promotes atrioventricular (AV) synchrony via accelerometer-based atrial sensing. Data regarding the real-world experience with this novel system are currently lacking. We sought to characterize patients undergoing MicraTM -AV implants, describe percentage AV synchrony achieved, and analyze the causes for suboptimal AV synchrony. Methods: In this retrospective cohort study, electronic medical records from 56 consecutive patients undergoing MicraTM -AV implants at the Mayo Clinic sites in Minnesota, Florida, and Arizona with a minimum follow-up of 3 months were reviewed. Demographic data, comorbidities, echocardiographic data, and clinical outcomes were compared among patients with and without atrial synchronous-ventricular pacing (AsVP) ≥70%. Results: Fifty-six percent of patients achieved AsVP ≥70%. Patients with adequate AsVP had smaller body mass indices, a lower proportion of congestive heart failure and pulmonary hypertension. Echocardiographic parameters and procedural characteristics were similar across the two groups. Active device troubleshooting was associated with higher AsVP. The likely reasons for low AsVP were persistent atrial arrhythmias, small A4-wave amplitude, and inadequate device reprogramming. Importantly, in patients with low AsVP, subjective clinical worsening was not noted during follow-up. Conclusion: With the increasing popularity of leadless PM, it is paramount for device implanting teams to be familiar with common predictors of AV synchrony and troubleshooting with MicraTM -AV devices.

An electrographic AV optimization for the maximum integrative atrioventricular and ventricular resynchronization in CRT

Background Atrioventricular (AV) delay could affect AV and ventricular synchrony in cardiac resynchronization therapy (CRT). Strategies to optimize AV delay according to optimal AV synchrony (AVopt-AV) or ventricular synchrony (AVopt-V) would potentially be discordant. This study aimed to explore a new AV delay optimization algorithm guided by electrograms to obtain the maximum integrative effects of AV and ventricular resynchronization (opt-AV). Methods Forty-nine patients with CRT were enrolled. AVopt-AV was measured through the Ritter method. AVopt-V was obtained by yielding the narrowest QRS. The opt-AV was considered to be AVopt-AV or AVopt-V when their difference was < 20 ms, and to be the AV delay with the maximal aortic velocity–time integral between AVopt-AV and AVopt-V when their difference was > 20 ms. Results The results showed that sensing/pacing AVopt-AV (SAVopt-AV/PAVopt-AV) were correlated with atrial activation time (Pend-As/Pend-Ap) (P < 0.05). Sensing/pacing AVopt-V (SAVopt-V/PAVopt-V) was correlated with the intrinsic AV conduction time (As-Vs/Ap-Vs) (P < 0.01). The percentages of patients with more than 20 ms differences between SAVopt-AV/PAVopt-AV and SAVopt-V/PAVopt-V were 62.9% and 57.1%, respectively. Among them, opt-AV was linearly correlated with SAVopt-AV/PAVopt-AV and SAVopt-V/PAVopt-V. The sensing opt-AV (opt-SAV) = 0.1 × SAVopt-AV + 0.4 × SAVopt-V + 70 ms (R2 = 0.665, P < 0.01) and the pacing opt-AV (opt-PAV) = 0.25 × PAVopt-AV + 0.5 × PAVopt-V + 30 ms (R2 = 0.560, P < 0.01). Conclusion The SAVopt-AV/PAVopt-AV and SAVopt-V/PAVopt-V were correlated with the atrial activation time and the intrinsic AV conduction interval respectively. Almost half of the patients had a > 20 ms difference between SAVopt-AV/PAVopt-AV and SAVopt-V/PAVopt-V. The opt-AV could be estimated based on electrogram parameters.

An electrographic AV optimization for the maximum integrative atrioventricular and ventricular resynchronization in CRT

Background:Atrioventricular (AV) delay could affect AV and ventricular synchrony in cardiac resynchronization therapy (CRT). Strategies to optimize AV delay according to optimal AV synchrony (AVopt-AV) or ventricular synchrony (AVopt-V) would potentially be in discordant. This study aimed to explore a new AV delay optimization algorithm guided by electrograms to get the maximum integrative effects of AV and ventricular resynchronization (opt-AV).Methods:Forty-nine patients with CRT were enrolled. AVopt-AV was measured through the Ritter method. AVopt-V was obtained by yielding the narrowest QRS. The opt-AV was considered to be AVopt-AV or AVopt-V when their difference was <20ms, and to be the AV delay with the maximal aortic velocity-time integral between AVopt-AV and AVopt-V when their difference was >20ms.Results:The results showed sensing/pacing AVopt-AV (SAVopt-AV/PAVopt-AV) were correlated with atrial activation time (Pend-As/ Pend-Ap)( P＜0.05 ). Sensing/pacing AVopt-V (SAVopt-V/PAVopt-V) were correlated with the intrinsic AV conduction time (As-Vs/Ap-Vs) (P＜0.01). The percentages of patients with more than 20ms differences between SAVopt-AV/PAVopt-AV and SAVopt-V/PAVopt-V were 62.9% and 57.1%, respectively. Among them, the opt-AV were linearly correlated with SAVopt-AV/PAVopt-AV and SAVopt-V/PAVopt-V. The sensing opt-AV (opt-SAV)=0.1×SAVopt-AV+0.4×SAVopt-V+70ms (R2=0.665, P<0.01) and the pacing opt-AV (opt-PAV)=0.25×PAVopt-AV+0.5×PAVopt-V+30ms (R2=0.560, P<0.01).Conclusion:The SAVopt-AV/PAVopt-AV and SAVopt-V/PAVopt-V were correlated with the atrial activation time and the intrinsic AV conduction interval respectively. Almost half of patients had a >20ms difference between SAVopt-AV/PAVopt-AV and SAVopt-V/PAVopt-V. The opt-AV could be estimated based on electrogram parameters.

Leadless pacing – next generation

In December 2013 leadless pacing system was implanted in humans for the first time. Both in IDE and PAR re­gistries high effectiveness and safety were confirmed. In the mentioned registries risk of severe complication was reduced by 48 and 63% respectively. The reduced risk was mainly shown in a decreased percentage of hospitali­zations and system revisions. MICRA VR system has activity detectors placed in three planes, which allows to detect onset and end of ventricular contraction as well as early, and atrial contraction related ventricular filling. This property allowed to design an algorithm to detect mechanical atrial contraction. This algorithm caused an increase in atrioventricular synchrony to 80,0 and 94,4% in patients with advanced AV block and preserved conduction, respectively. In patients with advanced AV block percentage of those who reached more than 70% of atrioventricular synchrony was 95%. Parameters which increase the likelihood of high percentage of AV synchrony are standard deviation of consecutive P-P intervals < 5/min. and lower E/A in echocardiography. Practical implementation of a new algorithm required redesigning of a circuit to reduce power consumption. New system MICRA AV was developed, which volume, mass and longevity are comparable with MICRA VR.