Determination of lead III Q waves significance. Utility of deep inspiration.

The relative clinical significance of lead III Q waves and the effect of inspiration has received added impetus after the finding that Q waves have predictive value for coronary artery disease and asynergy. We studied the effect of deep inspiration on Q waves in leads III and aVF in 31 patients and correlated it with the findings at cardiac catheterization. We found that phasic respiration can alter Q-wave duration significantly in leads III and aVF, regardless of the presence or absence of significant associated coronary artery disease and asynergy, and is therefore of no clinical value in this regard.