Improved evaluation of left ventricular hypertrophy using the spatial QRS-T angle by electrocardiography

Figures

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  Figure 1. Schematic illustration of the QRS-T angle, a vectorcardiographic measure derived from a digital resting 12-lead ECG. The vectorcardiogram represents the electrical activity in millivolts (mV) in three dimensions along the left–right, feet-head and anterior–posterior axes. The QRS loop (blue) and T loop (green) represent the direction and peak magnitude of depolarization and repolarization, respectively, of the left ventricle. The thick arrows show the largest magnitudes of the respective loops. The angle in three-dimensional space between the largest magnitude of the QRS loop and T loop is referred to as the spatial peaks QRS-T angle. (A) Schematic example of a normal QRS-T angle of 35° in a healthy volunteer. (B) Schematic example of an increased QRS-T angle of 80°.

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  Figure 2. Two representative examples of different QRS-T angles from the study. (A) A normal conventional 12-lead ECG in a healthy male in their 50s, with a corresponding derived vectorcardiographic spatial peaks QRS-T angle of 14° (normal). (B) A normal conventional 12-lead ECG in a male in their 80s with imaging-proven LVH, with a corresponding derived spatial peaks QRS-T angle of 134° (abnormal). HR denotes heart rate. Note, the QRS axis and T axis noted in the figure are from the frontal plane, whereas the spatial peaks QRS-T angle is calculated in three-dimensional space from the derived vectorcardiogram.

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  Figure 3. Sex-specific sensitivity or specificity for detecting anatomically defined left ventricular hypertrophy (LVH) in the respective cohorts. In both the Imaging-LVH and Clinical-Consecutive cohorts, an increased QRS-T angle had a higher sensitivity for LVH than all other ECG measures (p < 0.05 for all). Among females in the Healthy-Validation cohort, the specificity of the QRS-T angle for LVH was higher than that of QRS duration (p < 0.001), lower than Cornell product (p < 0.05), and did not differ significantly from that of the other measures (p > 0.05 for all). Among males in the Healthy-Validation cohort, the specificity of the QRS-T angle for LVH was higher than that of QRS duration (p < 0.001), lower than Cornell voltage and Cornell voltage product (p < 0.05 for both), and did not differ significantly from Sokolow-Lyon index (p = 0.12). In the Clinical-Consecutive cohort, the QRS-T angle had a lower specificity than the other ECG measures (p < 0.05 for all) despite its excellent specificity in the Healthy-Validation cohort, suggesting possible electrical identification of subclinical disease in patients who do not yet fulfill imaging criteria for LVH.

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  Figure 4. Area under the curve (AUC) for the evaluated criteria for detecting anatomically defined left ventricular hypertrophy. (A) AUC for the criteria in the combined Healthy-Validation and Imaging-LVH cohorts. (B) AUC for the criteria in the Clinical-Consecutive cohort.

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  Figure 5. Outcomes for patients in the Clinical-Consecutive cohort according to the presence of a normal or increased derived spatial peaks QRS-T angle, respectively, defined as ≥ 40° for females and ≥ 55° for males. An increased QRS-T angle was associated with worse outcomes in the form of survival free from heart failure hospitalization or all-cause death with events in 155 patients over a follow-up period of 5.7 [4.4–6.6] years.