ECG-derived spatial QRS-T angle is associated with ICD implantation, mortality and heart failure admissions in patients with LV systolic dysfunction

Abstract

Background: Increased spatial QRS-T angle has been shown to predict appropriate implantable cardioverter defibrilIator (ICD) therapy in patients with left ventricular systolic dysfunction (LVSD). We performed a retrospective cohort study in patients with left ventricular ejection fraction (LVEF) 31-40% to assess the relationship between the spatial QRS-T angle and other advanced ECG (A-ECG) as well as echocardiographic metadata, with all-cause mortality or ICD implantation for secondary prevention.

Methods: 534 patients ≤75 years of age with LVEF 31-40% were identified through an echocardiography reporting database. Digital 12-lead ECGs were retrospectively matched to 295 of these patients, for whom echocardiographic and A-ECG metadata were then generated. Data mining was applied to discover novel ECG and echocardiographic markers of risk. Machine learning was used to develop a model to predict possible outcomes.

Results: 49 patients (17%) had events, defined as either mortality (n = 16) or ICD implantation for secondary prevention (n = 33). 72 parameters (58 A-ECG, 14 echocardiographic) were univariately different (p<0.05) in those with vs. without events. After adjustment for multiplicity, 24 A-ECG parameters and 3 echocardiographic parameters remained different (p<2x10-3). These included the posterior-to-leftward QRS loop ratio from the derived vectorcardiographic horizontal plane (previously associated with pulmonary artery pressure, p = 2x10-6); spatial mean QRS-T angle (134 vs. 112°, p = 1.6x10-4); various repolarisation vectors; and a previously described 5-parameter A-ECG score for LVSD (p = 4x10-6) that also correlated with echocardiographic global longitudinal strain (R2 = - 0.51, P < 0.0001). A spatial QRS-T angle >110° had an adjusted HR of 3.4 (95% CI 1.6 to 7.4) for secondary ICD implantation or all-cause death and adjusted HR of 4.1 (95% CI 1.2 to 13.9) for future heart failure admission. There was a loss of complexity between A-ECG and echocardiographic variables with an increasing degree of disease.

Conclusion: Spatial QRS-T angle >110° was strongly associated with arrhythmic events and all-cause death. Deep analysis of global ECG and echocardiographic metadata revealed underlying relationships, which otherwise would not have been appreciated. Delivered at scale such techniques may prove useful in clinical decision making in the future.

Fig 1. Receiver operator curve for arrhythmic events classified by spatial QRS-T angle.

Spatial mean QRS-T angle >110° had a sensitivity 84%, specificity 50% and AUC 0.68 (95% C.I. 0.62 to 0.73, p<0.0001).

Fig 2. Kaplan Meier plot demonstrating primary event rates over time, dichotomized by a spatial mean QRS-T angle cut off of >110°.

Fig 3. Receiver operator curve for multiple machine learning models, generated using single decision trees and ensembles.

Fig 4. Kaplan Meier plot demonstrating heart failure admissions over time separated by spatial mean QRS-T angle >110°.

Fig 5. Receiver operator curve for heart failure admissions classified by spatial mean QRS-T angle.

Spatial mean QRS-T angle >147° had a sensitivity 64%, specificity 80% and AUC 0.74 (95% C.I 0.68 to 0.79, p<0.0001).

Fig 6. Scatter plot and regression line demonstrating relationship between global longitudinal strain and A-ECG 5-parameter LVSD score.

Fig 7. (a) Metadata network of patients without arrhythmic events, (b) all patients including those with events, demonstrating reduced complexity and increased path length.

Fig 8. Self-similarity network (a), and distributions (b & c) showing similarity between patients with primary events and between those with versus without primary events.