Towards the use of implanted cardiac leads or the diaphragm for active respiratory motion management in stereotactic arrhythmia radioablation.

Abstract

Purpose: To investigate the utility of implanted cardiac leads or the diaphragm for active respiratory motion management in stereotactic arrhythmia radioablation (STAR) by quantifying the relationship between their motions.

Methods and materials: Seven patients treated with STAR were imaged using 5 Hz bi-planar, kV x-ray fluoroscopy for 15-20 seconds under both abdominal compression (AC) and free breathing (FB) conditions. 3D motion traces for different regions of the heart were acquired by tracking and triangulating the position of all implanted cardiac leads. The heart's respiratory motion was extracted from the total motion (respiratory + cardiac) using a lowpass filter and described in optimized coordinates using Principal Component Analysis (PCA). The existence of a relationship between the respiratory motion of different cardiac leads or the diaphragm was quantified using the Spearman Rank Correlation Coefficient. Polynomial correlation models relating PC1 cardiac lead motion to the diaphragm were created and evaluated on the resultant errors.

Results: Eighty-one respiratory motion correlations between different positions of the heart or diaphragm were calculated under both AC and FB. Consistently strong correlations between the respiratory motion of different positions in the heart and the diaphragm required accounting for phase shifts between motions. When accounting for phase shifts, the proportion of strong (>0.7) PC1 respiratory motion correlations were 100% under FB and 92.6% under AC. Linear fitting of cardiac lead motion with the diaphragm resulted in mean absolute PC1 tracking errors of (1.0 ± 0.6) mm under FB and (0.7 ± 0.4) mm under AC.

Conclusions: The respiratory motion of all combinations of implanted cardiac leads and the diaphragm are moderately to strongly correlated after accounting for phase shifts between motion traces. These phase shifts should be carefully considered to ensure patient safety during respiratory tracking or gating during STAR using cardiac leads or the diaphragm as internal surrogates.