Differences in the upslope of the precordial body surface ECG T wave reflect right to left dispersion of repolarization in the intact human heart

Figure 1. Orientation of catheters in the heart and signal analysis. A: Schematic diagram showing positioning of catheters in an apicobasal orientation in the left ventricular (LV) endocardium (LVendo) and right ventricular (RV) endocardium, and transmurally across the lateral base of the LV epicardium (LVepi) via the coronary sinus, with corresponding unipolar electrograms recorded. B: Catheter positions were checked by fluoroscopy to ensure adequate apicobasal and transmural apposition. C: The Wyatt method was used to analyze repolarization time, with activation time (AT) measured as dv/dtmin of the QRS and repolarization time (RT) as dv/dtmax of the unipolar intracardiac electrogram (UEG) T wave. Activation recovery interval (ARI = RT – AT) was measured as a surrogate marker of action potential duration (APD). D: Schematic diagram of a single beat of the precordial ECG recorded in a patient during RV and LV pacing. Surface ECG markers including T-wave onset (Ton), Tpeak, and Tend were calculated for comparison across all leads during each S2 beat, allowing analysis of T-wave duration, Tpeak-Tend (TpTe), as well as differences across all leads in a single beat of earliest vs latest…

Figure 2. Unipolar T-wave amplitude regionally within the heart in relation to local repolarization time and body-surface 12-lead ECG amplitude. Rows depict mean and 95% confidence interval data for restitution pacing during right ventricular apical pacing (A), left ventricular basal endocardial pacing (B), and left ventricular basal epicardial (C) pacing. Epi = epicardium; LV = left ventricle; RT = repolarization time; RV = right ventricle; T-Amp = T-wave amplitude.

Figure 3. Proportion of right ventricular (RV) and left ventricular (LV) sites that repolarized before Tpeak on the precordial ECG leads, during RV apical endocardial pacing (A), LV basal endocardial pacing (B) and LV basal epicardial pacing (C). Endo = endocardial; Epi = epicardium; RT = repolarization time.

Figure 4. Relationship between repolarization measured in the intracardiac unipolar electrogram and the T wave in leads V1 and V6 on the surface ECG in a single patient during right ventricular (RV) endocardial (A), left ventricular (LV) endocardial (B), and left ventricular epicardial (Epi) (C) pacing. A–C: Simultaneously recorded unipolar electrograms from the RV and LV during a single pacing beat. Colors represent the electrograms in the base (red), mid (green), apex (blue), and epicardium (orange), along with the body surface ECG (black). Inset within each panel is focused view of the T wave, with range of measured regional repolarization moments overlaid on the body surface ECG T wave. Endo = endocardial.

Figure 5. Relationship between sensitivity (Sens) and specificity (Spec) of the T-wave upslope to repolarization time within regions of the heart, endo RV apex to base (A) LV endo mid to base and epi (B), LV endo apex (C). Endo = endocardium; Epi = epicardium; LV = left ventricle; RV = right ventricle.

Figure 6. Relationship between dispersion of repolarization in the major anatomic axis and markers on the surface ECG T-wave. A: Example of right to left dispersion of repolarization in relation to the difference between the end of the upslope in V1 minus the end of the upslope in V6. B: Example of the best correlation of Tpeak-Tend (TpTe) and transmural dispersion of repolarization, seen in V4. C: Example of the best correlation between apicobasal dispersion of repolarization and surface ECG markers, seen by measuring the difference between the end and the start of the T wave in lead aVL. ICC = intraclass correlation coefficient.