How to assess and treat right ventricular electromechanical dyssynchrony in post-repair tetralogy of Fallot: insights from imaging, invasive studies, and computational modelling

Abstract

Background and aims: Right bundle branch block (RBBB) and resulting right ventricular (RV) electromechanical discoordination are thought to play a role in the disease process of subpulmonary RV dysfunction that frequently occur post-repair tetralogy of Fallot (ToF). We sought to describe this disease entity, the role of pulmonary re-valvulation, and the potential added value of RV cardiac resynchronization therapy (RV-CRT).

Methods: Two patients with repaired ToF, complete RBBB, pulmonary regurgitation, and significantly decreased RV function underwent echocardiography, cardiac magnetic resonance, and an invasive study to evaluate the potential for RV-CRT as part of the management strategy. The data were used to personalize the CircAdapt model of the human heart and circulation. Resulting Digital Twins were analysed to quantify the relative effects of RV pressure and volume overload and to predict the effect of RV-CRT.

Results: Echocardiography showed components of a classic RV dyssynchrony pattern which could be reversed by RV-CRT during invasive study and resulted in acute improvement in RV systolic function. The Digital Twins confirmed a contribution of electromechanical RV dyssynchrony to RV dysfunction and suggested improvement of RV contraction efficiency after RV-CRT. The one patient who underwent successful permanent RV-CRT as part of the pulmonary re-valvulation procedure carried improvements that were in line with the predictions based on his Digital Twin.

Conclusion: An integrative diagnostic approach to RV dysfunction, including the construction of Digital Twins may help to identify candidates for RV-CRT as part of the lifetime management of ToF and similar congenital heart lesions.

Keywords: Cardiac resynchronization therapy; Digital Twin; Right bundle branch block; Right ventricular dysfunction; Tetralogy of Fallot.

Figure 1

Measured data from Patient #2 at invasive study during baseline condition and after RV-CRT. (A) Right ventricular and LV pressure curves from the invasive study. The timespan during end-systole at baseline in which RV pressure exceeds LV pressure (left) is abolished after RV-CRT (right). The PTP area depicts the related pressure–time product (PTP) (see Table 1 for respective data). (B) Right ventricular longitudinal segmental strain curves showing components of a classic dyssynchrony pattern at baseline with early basal, midventricular and apical septal contraction with accompanying stretch of the RV free wall (lateral basal and midventricular) segments followed by late contraction of the latter. During RV-CRT, all RV segments are contracting synchronously. AV close, aortic valve closure; LV, left ventricle; PV close, pulmonary valve closure; PTP, pressure–time product; RV, right ventricle; RV-CRT, RV cardiac resynchronization therapy.

Figure 2

Modelled data from Patient #2. The pressure–volume and strain–stress loops reflect the combination of RV volume load and dyssynchrony at baseline with major leftward shift of the loops after volume unloading and further change after RV-CRT. PVR, pulmonary valve replacement; RV-CRT, RV cardiac resynchronization therapy.

Figure 3

Modelled data from Patient #2 at baseline and after pulmonary re-valvulation, RV-CRT, and their combination. From top to bottom: (i) RV pressure curve. (ii) Modelled segmental strain curves displaying circumferential RV strain in individual RV segments and showing late mechanical activation of the RV free wall at baseline with major improvement of segmental shortening coordination after RV-CRT. (iii) Modelled calculation of systolic stretch fraction. Systole is defined as the time from QRS onset to latest peak negative strain (contraction end). The negative area under respective strain rate curves reflects systolic segmental shortening; the positive area corresponds with systolic segmental stretch. Paradoxical RV stretch during systole is greatly diminished after RV-CRT resulting in significant decrease in RV systolic stretch fraction. (iv) Modelled calculation of wasted work ratio using work performed by individual segments. Desceding parts of the segmental curves reflect negative work during systole and are displayed in red. Major decrease in RV wasted work ratio is seen after RV-CRT. LV, left ventricle; PTP, pressure–time product; RV, right ventricle; RV-CRT; TV close, tricuspid valve closure; TV open, tricuspid valve opening. For other abbreviations, see Figure 2.

Figure 4

Modelled data from Patient #2. The relationship between RV myocardial work and RV pump work is modelled at baseline and after RV-CRT as a function of (A) RV mechanical delay. (B) Pulmonary stenosis. (C) Pulmonary regurgitation. RV-CRT, RV cardiac resynchronization therapy.

Figure 5

Modelled data from Patient #2. Cardiac output at maximum exercise is displayed at baseline and after RV-CRT as a function of (A). RV mechanical delay. (B) Pulmonary stenosis. (C) Pulmonary regurgitation. RV-CRT, RV cardiac resynchronization therapy.