Algorithm for ventricular capture verification based on the mechanical evoked response.

Automatic pacemaker capture verification is important for maintaining safety and low energy consumption in pacemaker patients. A new algorithm was developed, based on impedance measurement between pacing electrode poles, which reflects the distribution of the conducting medium between the poles and changes with effective contraction. Data acquired during pacemaker implant in 17 subjects were analysed, with intracardiac impedance recorded while pacing was performed in the ventricle at varying energies, resulting in multiple-captured and non-captured beats. The impedance signals of all captured/non-captured beats were analysed using three different algorithms, based on the morphology of the impedance signal. The algorithm decision for each beat was compared with an actual capture or non-capture, as determined from the simultaneous recording of surface ECG. Two of the three algorithms (Z1 and Zn) were based on impedance values, and one (Z'n) was based on the first derivative of the impedance. Z1 was based on a single sample, whereas Z'n and Z'n were based on several samples in each beat. The total accuracy for each was Z1: 43%, Zn: 87%, Z'n: 92%. It was concluded that impedance-based capture verification is feasible, that a multiple rather than single sample approach for signal classification is both feasible and superior, and that first derivative analysis with multiple samples (Z'n) provides the best results.

Randomized comparison of J-shaped and straight atrial screw-in pacing leads.

OBJECTIVE: To study the importance of a J shape in atrial pacing leads. PATIENTS AND METHODS: We compared in a randomized controlled study acute and chronic results with 2 steroid-eluting, polyurethane, screw-in atrial lead models that differ only in shape. A total of 208 patients were randomized to have implantation of either a straight atrial lead (n = 105) or a J-shaped atrial lead (n = 103). Patients were followed up for 1 year. RESULTS: On implantation, there were no significant differences between leads in rates of failure to implant, implant measurements, number of attempts to achieve an acceptable position, and fluoroscopy times. Before discharge and at 3-month and 1-year follow-up, electrical measurements showed no statistical differences between leads. During the first year after implantation, there were 2.9% early dislodgments (< 1 week after implantation) and 2.9% late dislodgments in the straight lead group (5.9% rate of all dislodgments) vs no dislodgments in the J-shaped lead group (P = .01). There was a trend toward higher rates of exit block and lead malfunction in the J-shaped lead group. Rates of pericardial complications, subclavian/axillary thrombosis, and chronic atrial fibrillation were the same in both groups. CONCLUSIONS: Both leads appear to have an equally favorable performance profile for 1 year of follow-up. The J-shaped lead seems to be more stable and have fewer dislodgments, although it may have a somewhat higher malfunction rate.

Effect of implantable cardioverter-defibrillator shocks on QT dispersion.

Following transvenous implantable cardioverter defibrillator shocks, a significant increase in QT dispersion was observed. We suggest shock-induced increased dispersion of myocardial repolarization as one of the mechanisms of shock-induced proarrhythmia.