3582 - Resting Heart Rate Trends and Tachycardia among a Large Cohort of Patients Receiving Definitive Radiation Therapy for Solid Malignancies

Purpose/Objective(s): Cardiac toxicity is a well-recognized, but poorly understood complication associated with a broad range of cancer therapies including chemotherapy, immunotherapy, endocrine therapy and radiotherapy (RT). Recognizing the established relationship between resting heart rate and cardiovascular health in other settings, our objective was to longitudinally study the incidence and pattern of resting heart rate (rHR) elevation and de-novo tachycardia in a large cohort of unselected patients receiving definitive radiation therapy for non-metastatic cancer to characterize the contribution of radiation dose delivered in proximity to the heart versus other body parts.

Materials/Methods: Any adult patient with a non-metastatic solid malignancy treated in our department from 2018-2024 with photon-based RT was considered eligible for inclusion. Patients’ cancer type, radiation treatment course, total prescribed dose and fractionation scheme were obtained via retrospective chart review. Longitudinal measurements of resting heart rates were then captured at baseline (pre-RT), during RT, and for 6 months following RT using large-scale electronic health record (EHR) data mining. Associations between rHR elevation, tachycardia events (rHR>100 beats-per-minute) and cancer site (thoracic vs. non-thoracic) were evaluated using Cox and logistic regression analysis.

Results: In total, 7,981 patients were identified; median age was 72; 33% were female. Disease sites were as follows: lung (N=1,478), esophagogastric (N=700), bladder/prostate (N=3,677), rectum (N=762), CNS (N=674), and GYN (N=692), broken down into Thoracic (lung, esophagus, and gastroesophageal junction, 27%) and non-thoracic group (all others, 73%). Significant elevation in rHR was observed in the thoracic group (n=2,176), with rHR raising from 82±14 beats-per-minute (bpm) at the start (week 1) of RT to 93±16 at the end (last week) of RT (p<0.0001). The group of patients who did not receive radiotherapy to the thorax (n=5,805), in contrast, did not show any significant increase in rHR during RT (rHR=77±14 vs. 80±21 bpm, p=0.17). The risk of developing tachycardia during RT was significantly increased in the cohort receiving thoracic RT compared with the non-thoracic cohort (odds ratio=2.85, 95% CI=2.29-3.55, p<0.0001). In the thoracic group, the incidence of tachycardia (rHR100bpm) increased by 20%, from week 1 through the end of RT (0.11 ± 0.31 vs. 0.31 ± 0.46, p<0.0001).

Conclusion: In a large, unselected cohort of patients receiving RT for curative intent, thoracic RT was associated with an increased incidence of acute resting heart rate elevation and tachycardia events. Additional analyses of association of rHR with clinical endpoints and of dosimetric evaluation of cardiac substructure dose to identify the underlying structural driver behind elevation in rHR are ongoing.