Vectorcardiography as a Tool for Easy Optimization of Cardiac Resynchronization Therapy in Canine Left Bundle Branch Block Hearts

Abstract

In patients with left bundle branch block (LBBB) and heart failure, cardiac resynchronization therapy (CRT) aims to accomplish a more synchronous ventricular electric activation and contraction pattern by left ventricular (LV) based pacing, thereby improving LV systolic function. Clinical Perspective on p 552In applying CRT, optimizing the atrioventricular (AV) delay is important, because it determines the coupling between atrial and ventricular contraction, the dyssynchrony between the right ventricle (RV) and LV (interventricular dyssynchrony), as well as the dyssynchrony within the LV (intraventricular dyssynchrony). Current procedures for AV delay optimization use assessment of diastolic filling patterns and systolic function by echocardiography (mitral inflow or aortic outflow measurements) or invasive LV pressure measurements. Disadvantages of these procedures are that they are time consuming, complicated, expensive, and may even be inaccurate. 1In a previous study we have shown that optimal LV systolic function can be predicted using mechanical interventricular dyssynchrony (MIVD).2 In that study, performed in canine LBBB hearts as well as in CRT patients, a MIVD value halfway between its minimal (LV pacing with short AV delay) and maximal value (during LBBB or RV pacing) coincided with optimal systolic function. 2 We hypothesized that the QRS vector derived from the surface ECG reflects electric interventricular dyssynchrony and that, similar to the MIVD measurements, vectorcardiography (VCG) could be used to optimize LV stimulation timing in CRT.In the present study it was our aim to investigate whether VCG can be used as a relatively easy and noninvasive method Background-In cardiac resynchronization therapy (CRT), optimization of left ventricular (LV) stimulation timing is often time consuming. We hypothesized that the QRS vector in the vectorcardiogram (VCG) reflects electric interventricular dyssynchrony, and that the QRS vector amplitude (VA QRS ), halfway between that during left bundle branch block (LBBB) and LV pacing, reflects optimal resynchronization, and can be used for easy optimization of CRT. Methods and Results-In 24 canine hearts with LBBB (12 acute, 6 with heart failure, and 6 with myocardial infarction), the LV was paced over a wide range of atrioventricular (AV) delays. Surface ECGs were recorded from the limb leads, and VA QRS was calculated in the frontal plane. Mechanical interventricular dyssynchrony (MIVD) was determined as the time delay between upslopes of LV and right ventricular pressure curves, and systolic function was assessed as LV dP/dt max . VA QRS and MIVD were highly correlated (r=0.94). The VA QRS halfway between that during LV pacing with short AV delay and intrinsic LBBB activation accurately predicted the optimal AV delay for LV pacing (1 ms; 95% CI, -5 to 8ms). Increase in LV dP/dt max at the VCG predicted AV delay was only slightly lower than the highest observed ∆LV dP/dt max (-2.7%; 95% CI, -3.6 to -1.8%). Inability to reach the halfway value of VA QRS durin...

Electrophysiological and Hemodynamic Effects of Vernakalant and Flecainide During Cardiac Resynchronization in Dyssynchronous Canine Hearts

“…15,18 The present study also supports our earlier data that ENDO BiVP is to be favored over conventionally applied EPI BiVP with respect to indices of electrical dyssynchrony and pump function. 10 The relative increase in QRS width by Vernakalant and Flecainide observed in the present study is comparable with that in the previously reported studies that have FIGURE 2.…”

Transseptal Conduction as an Important Determinant for Cardiac Resynchronization Therapy, as Revealed by Extensive Electrical Mapping in the Dyssynchronous Canine Heart

“…The optimal LVdP/dt max consistently occurred at an interval where ATV epi and VA QRS were at values halfway between those during LBBB and LV pacing, supporting data from a previous study. 13 During AV optimization, the average interval offset was 2±11 ms for VA QRS and −9±24 ms for ATV epi (P=N.S. for both comparisons).…”

“…13 The VA QRS value halfway from LBBB and LV pacing at a short AV interval has been shown to predict maximal contractility response during AV/VV optimization. 13 For cardiac mapping electrograms, local depolarization times were calculated as the time difference between onset of the Q-wave (during baseline) or ventricular pacing artifact and the time of steepest negative deflection. Using custom MATLAB software (MathWorks, Natick, MA), the depolarization times were plotted on corresponding anatomic locations and on matched interpolated models.…”

Strategies to improve cardiac resynchronization therapy

“…In the canine model of LBBB, the amplitude of the QRS vector was found to be the electrical equivalent of mechanical dyssynchrony. 152 The QRS vector amplitude value halfway between intrinsic LBBB and fully captured LV pacing predicted the atrioventricular and interventricular delay of largest haemodynamic response. 152 Electrocardiographic optimization of CRT, therefore, might replace the need for separate echocardiographic and haemodynamic equipment and would substantially decrease the variability that affects haemodynamic measurements.…”