[Diagnosis of a Q3 wave: value of the inspiratory test]

The aim of this study was to determine the value of the inspiratory test on isolated Q waves in Lead III. The ECGs of 25 normal young adults with isolated Q waves in Lead III were compared with those of 86 patients with documented postero-diaphragmatic myocardial infarction (62 chronic, 21 recent). The criteria of abnormality of the Q waves were : duration 0.04 sec and amplitude 25% of R3. Thirty six per cent of the ECGs of the 25 normal subjects with the Q3 pattern met these criteria. Q3 post infarction changes may lose these pathological characteristics; they were absent in 23% of patients with chronic infarction and 17% of patients with recent infarction. Isolated Q3 changes, therefore, pose a difficult diagnostic problem. Lyle 's inspiratory test which is still widely used as a discriminating factor led to a reduction of the pathological Q wave amplitude and duration, both in normal subjects and in-patients who had documented infarction. The only difference between the 2 groups was the percentage decrease. Inspiration led to a reduction in the amplitude and duration of the Q3 waves in 89% of normal subjects, 58% of patients with chronic infarction and 20% of patients with recent infarction. Inspiration may even lead to the complete disappearance of the Q3 waves (10% of chronic infarcts). No correlations were found between the severity of the anatomical lesions (coronary or ventricular) and the reduction of Q3 waves. These results suggest that Lyle 's inspiratory test is a poor method of discriminating between normal and pathological isolated Q3 waves.