Electromechanics of the Normal Human Heart In Situ.

Abstract

November 2019 1 Knowledge of the spatiotemporal relationship between electrical excitation and mechanical contraction in the human heart is essential for understanding cardiac physiology and disease. However, electromechanical data from nondiseased human hearts are currently lacking. The present study is the first to combine Electrocardiographic Imaging (ECGI; a noninvasive method for cardiac electrophysiology mapping) with tagged magnetic resonance imaging (MRI) to study the electromechanics of healthy adult hearts in situ. This also represents the largest ECGI study of healthy adults to date. We provide 3-dimensional data of the normal cardiac electrical and mechanical activation sequences, obtained from the same hearts under complete physiological conditions. These are important baseline data for studies and diagnosis of cardiac disorders and for constraining computer models of the human heart. Twenty healthy adults were enrolled at Washington University in St. Louis. Healthy volunteer demographics are provided in Table I in the Data Supplement. The study was approved by the Human Research Protection Office at Washington University in St. Louis. All participants provided written informed consent. Data are available upon reasonable request. The ECGI method, developed and validated in our laboratory, was described previously.1 A schematic of the procedure is presented in Figure I in the Data Supplement. The method consists of recording ≈250 simultaneous ECGs from the torso, using electrode strips. Heart-torso geometries of subjects were imaged using a navigated anatomic MRI sequence. Electrode positions were marked with MRIvisible capsules. ECG recordings were combined with the heart-torso geometries to construct epicardial potentials and unipolar epicardial electrograms. Local activation times were computed from electrograms using the minimum dV/dt during the QRS, and recovery times using the maximum dV/dt during the T wave. Activation-recovery intervals (ARIs), a surrogate of local action potential duration, were computed by subtracting the local activation time from the local recovery time. Activation and recovery maps were edited based on overall sequence and neighboring electrograms. Tagged MR images were obtained and analyzed using previously described methods.2 ECG-gated images were obtained in short-axis and long-axis views for a complete cardiac cycle beginning at end diastole. Tagged and nontagged images were acquired during the same breath hold to ensure similar anatomic positioning. Tag lines in the myocardium were tracked and 3-dimensional displacements were calculated from the movement of intramural tag surface intersection points during systole. StressCheck software (ESRD, Inc, St. Louis, MO) was used to compute strain values throughout the left ventricle. Additional details of the ECGI and tagged MRI analyses are provided in the Data Supplement. SPECIAL REPORT