2022-01-02 17:53:12
الإجابة
D. Preexcitation
Preexcitation is correct. The electrocardiogram shows a
short PR interval (< 120 ms), slurred onset (called a delta
wave), and widening of the QRS (> 110 ms) is suggestive
of preexcitation. In a preexcited ECG, the accessory path-
way, by virtue of its ability to conduct quickly, activates a
portion of the ventricle before the depolarization of the
remaining part of the ventricle via the native conduction
system. This results in a fusion beat leading to wide and
often bizarre-looking QRS complex. Slurring at the begin-
ning of the QRS is called a delta wave. The width of QRS
depends on the relative contribution of the accessory
pathway–mediated ventricular activation. The greater the
myocardial activation is via the accessory pathway, the
wider the QRS complex will be. Severe LVH (choice A) is
incorrect. Left ventricular hypertrophy is diagnosed via
several criteria: The Sokolow-Lyon index is S in V1
plus R
in V4
or V5
equal to 35 mm or more, and R in aVL equal
to 11 mm or more. The Cornell criteria are S in V3
plus R
in aVL greater than 28 mm in men, and R in V2
plus R in
aVL greater than 20 mm in women. The Romhilt-Estes
score must be greater than 5 points, or be 4 points of the
following:
1) voltage criteria of R or S in limb leads ≥ 20 mm
(3 points), S in V1
or V2
≥ 30 mm (3 points), or R in V5
or V6
≥ 30 mm (3 points);
2) ST-T abnormalities such as ST-T vector opposite to
QRS (3 points) or ST-T vector opposite to QRS with
digoxin (1 point);
3) negative terminal P mode in V1
1 mm in depth and
0.04 sec (3 points);
4) left axis deviation (2 points);
5) QRS duration > 0.09 sec (1 point); and
6) delayed intrinsic inflection (1 point).
In the presence of preexcitation, diagnosis of LVH should
not be made.
Dextrocardia (choice B) is suggested by global negativity
(P, QRS, and T waves) will be seen in lead I and global
positivity is seen in lead aVR. Absent R-wave progression
is seen in precordial leads. Although negatively directed
QS complexes in the inferior lead suggests old inferior MI
(choice C), such a diagnosis cannot be made in the presence
of preexcitation. This is called the pseudoinfarction pattern.
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