Electromechanical predictors of haemodynamic and clinical efficacy of electro-mechanically optimised RV pacing for obstructive hypertrophic cardiomyopathy: a stratified analysis of EMORI-HCM

Background

EMORI-HCM was a multi-centre, blinded, randomised, cross-over trial of atrio-ventricular delay (AVD) optimised right ventricular pacing (RVP) in patients with symptomatic obstructive hypertrophic cardiomyopathy (oHCM) compared to back-up only RVP. The trial found RVP, delivered at electromechanically optimised AVD, improved symptoms measured by the Kansas City Cardiomyopathy Questionnaire (KCCQ-CSS), the ORBITA daily symptom app, peak VO2, and 6-minute walking distance.

In a secondary analysis, we tested whether baseline variables predicted the impact of pacing on clinical trial outcomes and acute haemodynamic response.

Methods

Sixty patients were randomised in EMORI-HCM. We measured the interaction between age, baseline PR interval, baseline unpaced QRS duration, baseline resting LVOT gradient, baseline presence of systolic anterior motion of the anterior mitral leaflet (SAM) and acute high-precision hemodynamic response on the symptom and functional end points using Bayesian ordinal models.

We then stratified the acute haemodynamic response by these predictors and additional echocardiographic parameters.

Results

There was limited evidence of an interaction between baseline QRS duration and the benefit of AVD-optimised RVP on KCCQ-CSS (Pr 87.4%), ORBITA Symptom App (Pr 88.8%), and peak VO2 (Pr 75.3%). There was good evidence of an interaction between SAM and the benefit of therapy on six-minute walking distance (Pr 99.9%) (Figure 1). There was some evidence of an interaction between left atrial diameter and acute haemodynamic response (Pr 94.5%). No other parameters exhibited evidence of interaction.

Conclusion

The benefit of AVD-optimised RVP in symptomatic patients with oHCM was consistent across most subgroups. An intrinsically narrow QRS may allow an exaggerated, beneficial dyssynchrony effect of pacing. SAM may identify obstruction localised to the LVOT where dyssynchrony has a more beneficial effect.Figure 1