BACKGROUND: Despite many advantages, leadless pacemakers are currently only capable of single-chamber ventricular pacing.
METHODS: The prospective MARVEL 2 (Micra Atrial tRacking using a Ventricular accELerometer 2) study assessed the performance of an automated, enhanced accelerometer-based algorithm downloaded to the Micra leadless pacemaker for up to 5 h in patients with AV block. The primary efficacy objective was to demonstrate the superiority of the algorithm to provide AV synchronous (VDD) pacing versus VVI-50 pacing in patients with sinus rhythm and complete AV block. The primary safety objective was to demonstrate that the algorithm did not result in pauses or heart rates of >100 beats/min.
RESULTS: Overall, 75 patients from 12 centers were enrolled; an accelerometer-based algorithm was downloaded to their leadless pacemakers. Among the 40 patients with sinus rhythm and complete AV block included in the primary efficacy objective analysis, the proportion of patients with ≥70% AV synchrony at rest was significantly greater with VDD pacing than with VVI pacing (95% vs. 0%; p
OBJECTIVE: The purpose of this study was to describe the natural history of acute elevated Micra vs traditional transvenous lead thresholds.
METHODS: Micra study VVI patients with threshold data (at 0.24 ms) at implant (n = 711) were compared with Capture study patients with de novo transvenous leads at 0.4 ms (n = 538). In both cohorts, high thresholds were defined as >1.0 V and very high as >1.5 V. Change in pacing threshold (0-6 months) with high (1.0 to ≤1.5 V) or very high (>1.5 V) thresholds were compared using the Wilcoxon signed-rank test.
RESULTS: Of the 711 Micra patients, 83 (11.7%) had an implant threshold of >1.0 V at 0.24 ms. Of the 538 Capture patients, 50 (9.3%) had an implant threshold of >1.0 V at 0.40 ms. There were no significant differences in patient characteristics between those with and without an implant threshold of >1.0 V, with the exception of left ventricular ejection fraction in the Capture cohort (high vs low thresholds, 53% vs 58%; P = .011). Patients with an implant threshold of >1.0 V decreased significantly (P < .001) in both cohorts. Micra patients with high and very high thresholds decreased significantly (P < .01) by 1 month, with 87% and 85% having 6-month thresholds lower than the implant value. However, when the capture threshold at implant was >2 V, only 18.2% had a threshold of ≤1 V at 6 months and 45.5% had a capture threshold of >2 V.
CONCLUSIONS: Pacing thresholds in most Micra patients with elevated thresholds decrease after implant. Micra device repositioning may not be necessary if the pacing threshold is ≤2 V.
METHODS AND RESULTS: The primary outcome (risk of cardiac failure, pacemaker syndrome, or syncope related to the Micra system or procedure) was compared between successfully implanted patients from the Micra IDE trial with a primary pacing indication associated with AF or history of AF (AF group) and those without (non-AF group). Among 720 patients successfully implanted with Micra, 228 (31.7%) were in the non-AF group. Reasons for selecting VVI pacing in non-AF patients included an expectation for infrequent pacing (66.2%) and advanced age (27.2%). More patients in the non-AF group had a condition that precluded the use of a transvenous pacemaker (9.6% vs. 4.7%, P = 0.013). Atrial fibrillation patients programmed to VVI received significantly more ventricular pacing compared to non-AF patients (median 67.8% vs. 12.6%; P
OBJECTIVE: The purpose of this study was to identify predictors of A4 amplitude and high AVS.
METHODS: We analyzed 64 patients enrolled in MARVEL 2 who had visible P waves on electrocardiogram for assessing A4 amplitude and 40 patients with third-degree AV block for assessing AVS at rest. High AVS was defined as >90% correct atrial-triggered ventricular pacing. The association between clinical factors and echocardiographic parameters with A4 amplitude was investigated using a multivariable model with lasso variable selection. Variables associated with A4 amplitude together with premature ventricular contraction burden, sinus rate, and sinus rate variability (standard deviation of successive differences of P-P intervals [SDSD]) were assessed for association with AVS.
RESULTS: In univariate analysis, low A4 amplitude was inversely related to atrial function assessed by E/A ratio and e'/a' ratio, and was directly related to atrial contraction excursion (ACE) and atrial strain (Ɛa) on echocardiography (all P ≤.05). The multivariable lasso regression model found coronary artery bypass graft history, E/A ratio, ACE, and Ɛa were associated with low A4 amplitude. E/A ratio and SDSD were multivariable predictors of high AVS, with >90% probability if E/A <0.94 and SDSD <5 bpm.
CONCLUSION: Clinical parameters and echocardiographic markers of atrial function are associated with A4 signal amplitude. High AVS can be predicted by E/A ratio <0.94 and low sinus rate variability at rest.
OBJECTIVE: The purpose of this study was to evaluate the system's performance during treadmill tests to maximum exertion in a subset of patients within the Micra Transcatheter Pacing Study.
METHODS: Patients underwent treadmill testing at 3 or 6 months postimplant with algorithm programming at physician discretion. Normalized sensor rate (SenR) relative to the programmed upper sensor rate was modeled as a function of normalized workload in metabolic equivalents (METS) relative to maximum METS achieved during the test. A normalized METS and SenR were determined at the end of each 1-minute treadmill stage. The proportionality of SenR to workload was evaluated by comparing the slope from this relationship to the prospectively defined tolerance margin (0.65-1.35).
RESULTS: A total of 69 treadmill tests were attempted by 42 patients at 3 and 6 months postimplant. Thirty tests from 20 patients who completed ≥4 stages with an average slope of 0.86 (90% confidence interval 0.77-0.96) confirmed proportionality to workload. On an individual test basis, 25 of 30 point estimates (83.3%) had a normalized slope within the defined tolerance range (range 0.46-1.08).
CONCLUSION: Accelerometer-based rate adaptive pacing was proportional to workload, thus confirming rate adaptive pacing commensurate to workload is achievable with an entirely intracardiac pacing system.