Strain and Pacing Study: The Effect of Pacing on the Mechanics of Cardiac Strain

Abstract

Aims: Our aim was to find a strain-based echocardiographic measurement that could detect a difference in the LV function cardiac mechanics between paced and intrinsic conduction. The study assessed strain-based measurements to identify whether they could differentiate between RV apical and RVOT pacing when comparing paced beats to intrinsic beats.

Methods: An observational study was performed on echocardiographic data from twenty-seven subjects (75 ±9.2 years) who received permanent pacemaker systems, then a combined pacemaker check and echocardiogram peri-procedurally. These subjects had normal underlying cardiac structure and function. The group was separated into RVA (n = 12) and RVOT (n = 15) for sub-group comparison. Parameters were assessed twice for each subject; during intrinsic and paced conduction, heart rates were matched. The strain parameters analysed included global longitudinal strain (GLS), radial strain and strain rate, global circumferential strain and strain rate, rotational strain and strain rate. Dyssynchrony was assessed using TDI analysis and speckle tracking radial strain methods. Traditional echocardiographic measures of ejection fraction, LVOT VTI and cardiac output were analysed. Time measurements were made from the onset of the QRS to; systolic onset, cessation, strain and strain rate peaks, for analysis of dyssynchrony and the sequence of mechanical events during intrinsic conduction for comparison to paced conduction. Systolic duration was calculated to evaluate when in systole mechanical events occurred.

Results: GLS was sensitive to changes in cardiac mechanics with pacing compared to intrinsic conduction (GLS(paced) = -13.90 ±6.33% compared to GLS(intrinsic) = -16.31% ±3.92%, p 0.0359). The change in GLS was more significant in the RVA sub-group (GLS(paced) = -12.93 ±4.53% compared to GLS(intrinsic) = -16.13% ±3.60%, p 0.0028), while GLS with RVOT pacing was similar to intrinsic conduction (GLS(paced) = -16.08 ±3.39% compared to GLS(intrinsic) = -16.08% ±4.28%, p 0.5989). None of the other strain-based parameters showed significant differences between paced and intrinsic beats. Dyssynchrony analysis was inconclusive, without significant difference between paced and intrinsic beats. QRS duration and cardiac axis altered with pacing in ways that have been well documented and reflect pacing lead site. Systole was temporally translated with pacing, occurring later, though this was unrelated to any increase in QRS duration. The significance of systole occurring later with pacing was unclear, though it is a definite mechanical change. There was no change in the sequence of cardiac events during systole.

Conclusion: GLS is sensitive to pacing induced changes in mechanics of LV function. GLS can differentiate between RVA and RVOT pacing, as RVOT pacing did not alter the cardiac mechanics as described by GLS. If these changes are observed in a longitudinal data series in patients with pacemakers, and predict deterioration in cardiac function, then they might be relevant to predict pacing-induced adverse events. If this were the case, then peri-procedural echocardiography could be used to determine when lead repositioning was required in this group.