Patient-specific quantification of cardiorespiratory motion for cardiac stereotactic radioablation treatment planning

Abstract

Background: Cardiac radioablation is a new treatment for patients with refractory ventricular tachycardia (VT). The target for cardiac radioablation is subject to cardiorespiratory motion (CRM), the heart's movement with breathing and cardiac contraction. Data regarding the magnitude of target CRM are limited but are highly important for treatment planning.

Objectives: The study sought to assess CRM amplitude by using ablation catheter geometrical data.

Methods: Electroanatomic mapping data of patients undergoing catheter ablation for VT at 3 academic centers were exported. The spatial position of the ablation catheter as a function of time while in contact with endocardium was analyzed and used to quantify CRM.

Results: Forty-four patients with ischemic and nonischemic cardiomyopathy and VT contributed 1364 ablation lesions to the analysis. Average cardiac and respiratory excursion were 1.62 ± 1.21 mm and 12.12 ± 4.10 mm, respectively. The average ratio of respiratory to cardiac motion was approximately 11:1. CRM was greatest along the craniocaudal axis (9.66 ± 4.00 mm). Regional variations with respect to respiratory and cardiac motion were observed: basal segments had smaller displacements vs midventricular and apical segments. Patient characteristics (previous cardiac surgery, height, weight, body mass index, and left ventricular ejection fraction) had a statistically significant, albeit clinically moderate, impact on CRM.

Conclusion: CRM is primarily determined by respiratory displacement and is modulated by the location of the target and the patient's biometric characteristics. The patient-specific quantification of CRM may allow to decrease treatment volume and reduce radiation exposure of surrounding organs at risk while delivering the therapeutic dose to the target.

Keywords: 3D mapping system; Cardiac radioablation; Cardiorespiratory motion; Stereotactic body radiation therapy; Ventricular tachycardia.

Figure 1

Quantification of cardiorespiratory motion. A: Total catheter displacement as a function of time during an ablation lesion. Two distinct families of oscillations can be appreciated—a high-frequency component corresponding to cardiac contraction and a lower-frequency component corresponding to respiratory motion. In this example, the respiratory component was evaluated at 13.6 mm. B: The total catheter displacement trace is processed to segment the catheter displacements generated by cardiac contraction. In this case, the average cardiac displacement was evaluated at 3.0 mm.

Figure 2

Average cardiorespiratory motion (CRM). Top: Average cardiac (A) and respiratory (B) contribution to CRM per vector direction (X: mediolateral; Y: craniocaudal; Z: anteroposterior) and in total (cardiac vs respiratory) (C). Bottom: Average cardiac (D) and respiratory (E) contribution to CRM per subgroup of cardiomyopathy/ablation area. F: Ratio of respiratory to cardiac contribution to CRM. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001. ICM = ischemic cardiomyopathy; NICM = nonischemic cardiomyopathy; ns = not significant; OT = outflow tract; RV = right ventricle.

Figure 3

Vectorial cardiorespiratory motion. Average respiratory (A) and cardiac (B) motion along the 3 orthogonal axes. Both are normalized to the largest component (ie, respiratory craniocaudal motion).

Figure 4

Segmental cardiorespiratory motion. Top: Cardiac displacement per region (basal, midventricular, apical) (A) and per segment (B). Bottom: Respiratory displacement according to region (C), and regional and segmental movement analysis (D) included only left ventricular data. ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001. ns = not significant.

Figure 5

Cardiac and respiratory displacement and their respective association with patient and clinical characteristics. Top: Association of cardiac excursion with patient and clinical characteristics. Bottom: Association of respiratory excursion with patient and clinical characteristics. ∗P < .05; ∗∗∗P < .001; ∗∗∗∗P < .0001. BMI = body mass index; LVEF = left ventricular ejection fraction; ns = not significant.