Welch Allyn Means ECG Physicians Manual for CP Series Electrocardiographs - User Manual - Manual (Page 19)

MEANS Physicians Manual
Welch Allyn
19
2.15 Infarction
This section of the program classifies an infarction according to location and estimates the
probability of its presence. The diagnosis of infarction is largely based on the presence and
duration of Q waves, Q/R ratios, and QS patterns. T and ST abnormalities are used in
statements on the age of the infarct (see section Repolarization).
The location of the infarction is determined by the leads in which the abnormalities are found.
The program distinguishes six locations: septal (lead V1, V2), anterior (V3, V4), lateral (V5,
V6), high lateral (I, aVL), inferior (aVF, III), and posterior (V1, V2). Lead II may be involved in
inferior infarction as well as in lateral infarction. Combined and more extensive infarcts will
generate infarct statements for more than one location (see section Combination of
statements).
Four degrees of probability are distinguished: “definite”, “probable”, “possible”, or “consider”.
Criteria on which a diagnosis of infarction has been made can also lead to other diagnoses,
like LBBB, RBBB, LVH and RVH. The choice between these possible diagnoses is based on
exclusion logic in the program, and in some situations, probabilities are adapted or criteria are
tightened.
Inferior infarction
An abnormal Q wave must be found in aVF and either II or III to even consider the diagnosis
of inferior infarction. As a rule the Q wave in aVF is shallower and shorter than that in III. Its
threshold to qualify as an infarct Q can therefore be lower.
Inferior infarction may produce a left (i.e., superior) axis deviation if one only considers the
ratio of upward and downward forces. In inferior myocardial infarction, however, this ratio is
shifted due to initial negativity (Q in aVF) whereas in ordinary left axis deviation it is
associated with deepening of the S wave in aVF.
Skip tests
if:
Q amplitude + R amplitude in aVF < 200 µV
or Q amplitude in aVF  100 µV
or Q amplitude in II

70 µV
and Q amplitude in aVF

70 µV
or Q amplitude in III  100 µV
Say:
“inferior infarct”
if: Q duration

40 ms and Q/R ratio

0.3 in aVF
Say:
“probable inferior infarct”
if: Q duration

40 ms and 0.2

Q/R ratio < 0.3 in aVF
or 30

Q duration < 40 ms and Q/R ratio

0.3 in aVF
or Q duration in aVF

20 ms
and Q duration

50 ms and Q amplitude > 300 µV in III
Say:
“possible inferior infarct”
if: 30

Q duration < 40 ms and 0.2

Q/R ratio < 0.3 in aVF
or 20

Q duration < 30 ms and Q/R ratio

0.3 in aVF
and Q duration in III

40 ms
or Q duration in aVF

20 ms
and 40

Q duration < 50 ms and Q amplitude > 300 µV in III