[Duration of the atrial QT (QTa) under normal conditions and its values in atrial damage]

Atrial QT(QTa) was measured in lead II, in right thoracic leads V4R, V3R and V1 as well as in five direct atrial unipolar leads in 40 dogs. Atrial damage of right or left atrium was provoked by infiltration of 96 degree alcohol in 30 dogs Premature right atrial beats were induced till one was blocked and A-V block was provoked in 10 other normal dogs as well as in those with right atrial damage. Control QTa was observed to include the terminal QRS notch and the proximal irregularity on ventricular ST interval that was better seen in direct leads with sinus rhythm and confirmed later in A-V block and blocked atrial premature beats. It was concluded that normal corrected QTa (QTac) can be obtained by QTac = 0.32 2 square root P-P +/- 0.02. In atrial damage the value increases beyond + 0.04 inclusive + 0.013 with the greater values in the right atrial unipolar. This formula allow us to recognize normal or abnormal QTac duration and to be acquainted that the terminal notch of QRS is produced by the final forces of atrial recoviry in some cases as well as to determine the position of vulnerable atrial period on the ST ventricular segment with and without atrial damage.