Clinical evaluation of two different evoked response sensing methods for automatic capture detection in the left ventricle.

BACKGROUND: This acute feasibility study compared two different automatic capture detection methodologies, the reduced coupling capacitor (RCC) and the independent pace/sense (IPS) methods, for the left ventricle (LV). METHODS: LV threshold tests were performed in DDD mode, with LV-only and bi-ventricular (BiV) pacing using an external cardiac resynchronization therapy (CRT) defibrillator. Evoked response (ER) signals from LV leads were recorded using the LV(Tip) (LV(Tip)-->Can) and LV(Ring) (LV(Ring)-->Can) to empty pulse generator (Can) housing sensing vectors to evaluate the two methodologies. Pacing vector, pulse duration, atrioventricular delay, and interventricular delay were varied to assess their effects on ER. The minimum ER amplitude (ER(min)), signal-to-artifact ratio (SAR), and ER amplitude voltage dependence were evaluated. ER(min)>2 mV and SAR(min)>2 define potential automatic LV capture detection for the two methodologies. RESULTS: Data collected from 43 patients (63.7 +/- 11.0 years) were analyzed, including unipolar and bipolar (14/29) LV leads. Neither ER sensing method was affected by changing the pacing vector. The LV(Tip)-->Can ER(min) was significantly decreased at the 1.0-ms pulse duration when compared to 0.4-ms (p < 0.05). During BiV pacing, LV(Tip)-->Can ER(min) increased at negative interventricular delays and decreased at positive interventricular delays relative to simultaneous pacing. LV(Tip)-->Can resulted in fewer patients with sufficient ER characteristics for capture detection, albeit only significantly at the extended pulse duration (79% vs 97%, p < 0.05) and at simultaneous and positive interventricular delays (81% vs 97%, p < 0.05). CONCLUSIONS: Though LV capture detection was feasible using both investigated methods, the RCC method (LV(Tip)-->Can) sensitivity to the evaluated pacing parameters suggests the IPS method (LV(Ring)-->Can) provides a more robust performance.

Electrical pacing counteracts intrinsic shortening of action potential duration of neonatal rat ventricular cells in culture.

Previous studies have demonstrated the relationship between the functional electrophysiological properties of cultured neonatal rat ventricular myocytes (NRVMs) and the ability of the substrate to induce and sustain arrhythmia. The goal of this study was to examine the effects of chronic pacing at a constant rate akin to that in vivo, on the functional electrophysiological properties of NRVM monolayers. Confluent NRVM monolayers grown on 20 mm diameter cover slips were left either unpaced or were stimulated at 3 Hz for the duration of the culture, and were optically mapped on days 4, 6, or 8. Action potential duration at 80% repolarization (APD80), conduction velocity (CV), and Kv4.3 (Ito) and NCX protein expression were measured. The effects of the excitation-contraction uncoupler 2,3-butadione monoxime (BDM) were also investigated. The 2 Hz APD80 of non-paced monolayers decreased significantly on days 6 (137.1+/-13.9 ms) and 8 (109.8+/-9.0 ms) compared with day 4 (197.0+/-11.8 ms), while that of paced monolayers did not (206.8+/-9.7, 209.1+/-9.2, and 210.6+/-9.9 ms, respectively). The 2 Hz CV of non-paced monolayers increased significantly on days 6 (26.0+/-1.6 cm/s) and 8 (26.5+/-1.0 cm/s) compared with day 4 (20.0+/-1.0 cm/s), while that of paced monolayers did not change significantly (26.0+/-2.0, 26.0+/-1.0, and 23.8+/-1.2 cm/s, respectively). The restitution curves of APD80 and CV of paced monolayers were also unchanging from days 4 through 8. Despite the unchanging APD80 and CV, a decrease in Kv4.3 expression and an increase in NCX expression were observed in paced compared with non-paced monolayers. Cessation of pacing or administration of BDM caused a reversal of phenotype back to that of non-paced monolayers. In summary, chronic electrical stimulation of confluent NRVM monolayers results in stabilization of APD80 and an advancement of the developmental rise of CV that is mediated by electromechanical coupling. These effects produce a steadier functional phenotype that may be beneficial for electrophysiological studies.

Acute performance evaluation of a new ventricular automatic capture algorithm.

AIMS: This study evaluated the acute clinical performance of a new ventricular automatic capture algorithm developed to work with all lead types and pacing vectors. METHODS AND RESULTS: During regular pacemaker implant or replacement, AutoThreshold and manual threshold tests were performed in ventricular unipolar (UP) and bipolar (BP, if applicable) pacing using a customized external prototype INSIGNIA pacemaker. The success rate and accuracy of two different modes (commanded and ambulatory) of the automatic capture algorithm were used to evaluate the performance. Loss-of-capture events (two consecutive non-captured beats without backup pacing) were used to assess safety. Data of 53 patients (33 DDD/20 VVI) from four medical centres were analysed. Tested leads included 43 BP and 10 UP from nine manufacturers, and seven had electrodes with low polarization. The rate of successful commanded and ambulatory AutoThreshold tests was 96 and 94%, respectively, with an average absolute threshold difference compared with manual threshold of < 0.1 V at 0.4 ms (commanded 0.07 +/- 0.07 V and ambulatory 0.08 +/- 0.07 V). There was no significant difference in performance between UP/BP pacing, polarization, and lead type. No loss-of-capture event was observed. CONCLUSION: When successful, the ventricular automatic capture algorithm accurately determined pacing thresholds in either a UP or BP pacing configuration among all leads tested.