Mechanical QT and JT intervals by M-mode echocardiography: An extrapolation from the concurrent electrocardiographic tracings

Background: Congenital long QT syndrome (CLQTS) is a life-threatening ion channelopathy leading to syncope and sudden death. Early diagnosis during the prenatal period and timely intervention can prevent sudden cardiac death and catastrophic consequences of this genetic ion channelopathy. Fetal magnetocardiography and fetal electrocardiography (ECG) enable the measurement of fetal QT and JT intervals, but their inherently technically challenging and/or resource-intensiveness nature preclude their routine clinical application. On the other hand, the high-temporal resolution of M-mode echocardiography makes it a well-suited and widely available modality for the measurement of cardiac events.

Aims and objectives: We aimed to investigate the mechanical counterparts of the electrical QT and JT intervals on M-mode echocardiographic images of the tricuspid, mitral and aortic valves, and aortic wall.

Methods: We performed a prospective study on consecutive children referred to the outpatient pediatric cardiology clinic at a tertiary children's hospital. We defined M-mode echocardiographic landmark points on tracings of tricuspid annular planar systolic excursion, mitral and aortic valves, and aortic wall with simultaneous electrocardiographic recording. We measured the mean±SD of the absolute time difference and RR-adjusted time difference in cases with non-coincident ECG events and echocardiographic landmarks.

Results: Fifty healthy children were enrolled in the study. In 47 (94%) out of the 50 children, Q was coincident with the starting point of the tricuspid annular plane systolic excursion. In all children, the Q was coincident with the mid-point of the A-C line of the mitral valve. In 38 (76%) cases, there was a bump on the anterior wall of the aortic root immediately before the change in the slope of the aortic wall. This was coincident with the Q wave in 100% of cases. In all cases, the J point coincided with the point of acceleration of velocity on TAPSE. In all children, the J point coincided with the initial maximal opening of the aortic cusps. The end of the T wave occurred coincident with the peak of the tricuspid annular planar systolic excursion in 47 children (94%). In 48 children (96%), the end of the T wave coincided with the aortic cusps' closure point.

Conclusions: Based on our findings, we propose to measure the averaged mechanical QT and JT intervals by using an angled M-mode tracing of the aortic and mitral valve in five consecutive beats in the parasternal long-axis view. This is the first study on mechanical QT and JT intervals in healthy children. The study opens the horizons into the in-utero diagnosis of congenital long QT syndrome by measuring fetal QT and JT intervals using the widely available M-mode echocardiography.