Veerichetty Kadhiresan

Automatic Capture Verification by Charge‐Neutral Sensing

Automatic capture verification can prolong pulse generator longevity and increase patient safety. However, the detection of evoked response following pacing is complicated due to afterpotentials caused by polarization of electrodes. This study describes a new capture verification scheme, which neutralizes the charges between the pacing electrodes. The hypothesis of the charge‐neutral sensing is that the afterpotentials in the ring and the tip are opposite in polarity when pacing in a bipolar mode between ring and tip. Summing the unipolar signals sensed at the tip and the ring should effectively cancel the afterpotentials. This scheme was implemented in an external computer based system and tested during pacemaker implant/replacement on 23 patients during VVI pacing (17 acutely implanted leads and 6 chronic leads). Surface ECG was recorded to provide a marker for capture and noncapture. The pacing voltage was gradually decreased until a noncapture beat was noted. To avoid fusion beats, the pacing rate was programmed ˜50% higher than the intrinsic rate. The evoked response was high pass filtered and the integral average was calculated for both capture and noncapture beats. The system signal to noise ratio (SNR) was expressed as ratio of the minimum integral average of all capture beats to the maximum integral average of all noncapture beats. The system SNR was 8.6 ± 1.3 (mean ± S.E.M; range 1.5–22.8), indicating that the charge‐neutral sensing method has, on average, a ninefold safety margin in providing capture verification. Further, evaluation is needed to fully assess this feature in patients with chronic leads.

Comparison of paced and intrinsic ECG characteristics for measurement of pacing threshold

Accurate determination of pacing threshold is required for increased longevity of pacemakers and to ensure contraction of the heart. During pacing threshold measurements, surface ECG analysis is necessary for capture verification. Time and frequency domain characteristics of paced and intrinsic surface ECG events were analyzed in 12 pacemaker patients. When compared with amplitude and slew rate, the QRS area provides the best possible discrimination between paced and intrinsic events. Frequency analysis indicates that the power spectrum of a paced ECG is distributed over a shorter frequency range when compared with the intrinsic ECG event. Parameters either in the time or frequency domain or both can be utilized to develop an algorithm for automatic determination of pacing threshold.

Optimizing cardiac resynchronization therapy in heart failure patients by measuring transient changes in sinus rate during pacing

To optimize cardiac resynchronization therapy (CRT) for chronic heart failure (CHF) patients, acute studies show that left ventricular pacing site and atrio-ventricular (AV) delay can be individualized to maximize aortic pulse pressure (PP) increase. In the normal patient it is known that atrial cycle length (ACL) increases as PP increases via the baroreceptor reflex. Therefore, we evaluated another parameter for optimization of pacing parameters - transient ACL, or inversely, sinus heart rate. In a retrospective study, 29 CHF patients, acutely implanted to measure ACL and aortic PP, each received atrial-triggered ventricular pacing in 15 different randomized combinations of 3 pacing sites and 5 AV delays. Each trial contained 15 intrinsic beats (no pacing) and 5 paced beats; PP and ACL changes with pacing were averaged over. the 5 trials. The pacing combination with maximum ACL increase was hypothesized to be statistically related to maximum PP increase. For patients responding to pacing therapy (N = 20), the ACL algorithm predicted optimal or near-optimal (PP increase > 75% of optimal) pacing combinations for most of these patients (85%) and predicted combinations yielding 50-75% of optimal for the rest (15%). This paper describes an algorithm for optimizing PP response via transient ACL measurements. The ACL algorithm may allow rapid and minimally invasive optimization of pacing site and AV delay for CRT in CHF patients.

Hemodynamic effects of multisite ventricular pacing in dogs at short atrioventricular delay

The effects of VDD pacing on hemodynarnics can be best studied at a short atrioventricnlar (SAVD) since it avoids fusion with the intrinsic wave generated at the atrium. Although studies have been done to test right ventricular apex (RVA) pacing with short AV delay, little is known about pacing at different sites in the left ventricle (LV) with a normal conduction system. Our aim was to compare the hemodynarnic effects of different activation sequences with SAVD pacing in a normal conduction system.