Effects of deep inspiration on QRS axis, T-wave axis and frontal QRS-T angle in the routine electrocardiogram

The frontal QRS-T angle on the electrocardiogram has been described as a variable of ventricular repolarization. We evaluated how deep inspiration affected QRS axis, T-wave axis and frontal QRS-T angle. We also assessed the effects on left ventricular volume on the association using myocardial perfusion SPECT. Fifty patients undergoing ECGs both in resting state and in deep inspiration and subsequent SPECT were enrolled. Frontal QRS-T angle was defined as the absolute value of the difference between the frontal QRS axis and T-wave axis. Change in frontal QRS-T angle was calculated using (QRS-T angle in deep inspiration-QRS-T angle in resting state). In resting state, QRS axis and T-wave axis were 20.9° ± 30.0° and 40.9° ± 36.1°, respectively. Frontal QRS-T angle was 35.9° ± 36.1°. Deep inspiration caused rightward shifts of QRS axis (42.3° ± 29.5°, p < 0.001) and T-wave axis (49.5° ± 39.7°, p < 0.001). However, deep inspiration did not affect frontal QRS-T angle (33.9° ± 35.8°, p = 0.44). Frontal QRS-T angle in deep inspiration had good correlation (r = 0.87, p < 0.001) and agreement with that in resting state. Left ventricular (LV) end-diastolic volume had a significant association with change in frontal QRS-T angle (r = 0.29, p = 0.04). Our data suggest that frontal QRS-T angle in deep inspiration has a good correlation with that in resting state, and the agreement is acceptable. In patients with dilated LV, QRS-T angle in deep inspiration may be susceptible to the overestimation.