Automated detection of effective left-ventricular pacing: going beyond percentage pacing counters

Abstract

Aims: Cardiac resynchronization therapy (CRT) devices report percentage pacing as a diagnostic but cannot determine the effectiveness of each paced beat in capturing left-ventricular (LV) myocardium. Reasons for ineffective LV pacing include improper timing (i.e. pseudofusion) or inadequate pacing output. Device-based determination of effective LV pacing may facilitate optimization of CRT response.

Methods and results: Effective capture at the LV cathode results in a negative deflection (QS or QS-r morphology) on a unipolar electrogram (EGM). Morphological features of LV cathode-RV coil EGMs were analysed to develop a device-based automatic algorithm, which classified each paced beat as effective or ineffective LV pacing. The algorithm was validated using acute data from 28 CRT-defibrillator patients. Effective LV pacing and pseudofusion was simulated by pacing at various AV delays. Loss of LV capture was simulated by RV-only pacing. The algorithm always classified LV or biventricular (BV) pacing with AV delays ≤60% of patient's intrinsic AV delay as effective pacing. As AV delays increased, the percentage of beats classified as effective LV pacing decreased. Algorithm results were compared against a classification truth based on correlation coefficients between paced QRS complexes and intrinsic rhythm QRS templates from three surface ECG leads. An average correlation >0.9 defined a classification truth of ineffective pacing. Compared against the classification truth, the algorithm correctly classified 98.2% (3240/3300) effective LV pacing beats, 75.8% (561/740) of pseudofusion beats, and 100% (540/540) of beats with loss of LV capture.

Conclusion: A device-based algorithm for beat-by-beat monitoring of effective LV pacing is feasible.

Keywords: Cardiac resynchronization therapy; Effective LV pacing; Electrograms; Percent pacing.

Figure 1

(A) Conceptual diagrams of LV cathode–RV coil EGMs following left-ventricular (LV) pacing that are characteristic of (i) effective LV pacing, (ii) ineffective LV pacing from loss of capture, and (iii) ineffective LV pacing from pseudofusion. The dotted horizontal line shows the isoelectric (zero-voltage) line for each plot. The horizontal portion of the solid line results from post-pace blanking of the EGM, which can conceal the actual EGM (dashed line in iii). (B) Morphological features considered in the development of an effective biventricular pacing algorithm, baseline amplitude (BL), maximum amplitude (Max), and time to maximal amplitude (T_max), minimum amplitude (Min), and time to minimal amplitude (T_min). These parameters were calculated from the unipolar electrogram signal within a 170 ms window starting from the time at which pacing was delivered. EGM, electrogram; LVP, LV pacing.

Figure 2

LV tip–RV coil EGM morphologies during BV pacing (top, left), LV-only pacing (top, right), and RV-only pacing (bottom) at varying programmed AV intervals. The patient's intrinsic AV delay was 190 ms. All EGMs during BV and LV pacing had QS/QS-r morphologies except for the ones corresponding to the longest AV delay of 180 ms. The EGMs during RV-only pacing had broad R-waves.

Figure 3

LV tip–RV coil EGM (left) and surface QRS complexes (right) during BV pacing vs. intrinsic rhythm at varying programmed AV intervals. Three precordial leads, V1, V3, and V6 are shown. Each panel on the right overlays the BV-paced QRS complex (blue) along with the intrinsic QRS template (red), and shows the correlation coefficient (r) between the paced and the intrinsic complexes. The correlation coefficient between intrinsic and paced QRS complex at the longest AV delay (180 ms), was >0.9 for each of the three leads. The X-axis is in milliseconds and Y-axis is in milliVolts.

Figure 4

LV tip–RV coil EGM (left) and surface QRS complexes (right) during LV pacing vs. intrinsic rhythm at varying programmed AV intervals. Three precordial leads, V1, V3, and V6 are shown. Each panel on the right overlays the LV only paced QRS complex (blue) along with the intrinsic QRS template (red) and shows the correlation coefficient (r) between the paced and the intrinsic complexes. The paced surface complexes at the longest AV interval (180 ms) were similar to intrinsic. The X-axis is in milliseconds and Y-axis is in milliVolts.

Figure 5

Effective percentage of LV pacing as a function of programmed AV interval for all patients (n = 28). For programmed AV delays up to 60th percentile of intrinsic, the algorithm classified all beats as effective pacing. For AV delays >90th percentile, all beats were classified as ineffective pacing.

Figure 6

Comparison of performance (sensitivity/specificity) of the effective LV pacing algorithm for different thresholds of average correlation coefficient between paced QRS and intrinsic QRS (used for discriminating ineffective from effective LV pacing) at three precordial leads V1, V3, and V6. The curve on the right (circles) shows the sensitivity/specificity values for effective pacing vs. pseudofusion, the curve on the left (triangles) shows the corresponding values for effective pacing vs. loss of capture. The different correlation thresholds used for detecting pseudofusion from surface ECG are also shown in the figure.