Pettinati
G. - Manca L. - De Santis F. - Muscella A.
Divisione
di Cardiologia - Ospedale "F.Ferrari" - Casarano
Several
non invasive methods (holter monitoring, heart rate variability,
signal averaged electrocardiogram, baroflex sensitivity) are
available to predict ventricular arrhythmias during acute myocardial
infarction; however none of them is highly specific or sensitive. Many
authors have suggested QT dispersion during myocardial infarction to be
marker of electrical instability, although its prognostic role has not
been fully established. Aim of this study, was evaluate QT dispersion in
patients with acute myocardial infarction, in order to compare it with
QT dispersion in normal subjects and to assess its correlation with
severe ventricular arrhythmias in the early phase of myocardial
infarction.
MATERIALS
AND METHODS
We
studied 88 patients 54 male - 34 female, age 65 +/- 10 y with acute
myocardial infarction admitted consecutively to our coronary care unit
within 12 hours after onset of typical chest pain. Patients with
previous acute myocardial infarction or other heart diseases, atrial
fibrillation, bundle brunch block and/or those undergoing treatment with
antiarrhytmic agents or drugs known to affect the QT interval (except
for beta -blockers) were excluded from the study. We macthed the
patients with a control group of 30 healtly subjects. Their gender and
age were comparable to those of the patients acute myocardial infarction.
Standard
12 - lead electrocardiograms were performed on all the patients with
acute myocardial infarction at a paper speed of 25 mm/s on a
three-channel recorder 10 days after the onset of symptom. All
electrocardiograms were examined blindly by one observer. QT intervals
were measured manually
from the onset of the QRS complex to the end of T wave, defined
as the return to the TP isoelectric baseline. When U waves were present,
the QT interval was measured to the nadir of the curve between the T and
U waves. Three consecutive cycles were measured in each of the standard
12 leads and the mean QT was calculated. If the end of T wave could not
be determined reliably or when T waves were isoelectric or of very low
amplitude, the lead was excluded from the analysis. A minimum of seven
leads, at least three of which precordial, was required for inclusion in
this study. QT dispersion was calculated as the difference between the
maximum and minimum QT intervals measured in each of the 12-lead
electrocardiograms. At all patients were performed a ECG Holter 24/h,
Ventricular Late Potential, (Simson
Tecnique, filter 25 - 40 Hz and noise < 0,5) and Ejection
Fraction by ecochardiography Simpson method.We considered signicantly
patological QT dispersion >80 ms (Pulievich 1997). RESULTS
We
found statistically no significant differences in QT dispersion between
the electrocardiograms performed on healthy subjects (44+/- 13,4ms)
and the electrocardiograms performed
on patients with acute myocardial infarction at
day 10 (48,9
+/- 42). We studied the patients treated with and without thrombolytic
therapy
and we found no significant difference between the groups. We
matched QT dispersion of patients with and without severe ventricular
arrhythmias. We found during in hospital stay 5 patients with severe
ventricular arrhythmias, 2 TV - FV and 3 non sustained TV (5,6%), after
48/hours from AMI. Only 2 of
5 patients has QT dispersion
> 80 ms (105 and 100 ms). Age, gender,
and CPK level did not influence QT dispersion. Late potential are
present in 16/88 (18%) patients but in none with severe ventricular
arrhythmias. Left ventricular F.E. was 48,3 +/- 8 % (range 38 - 55%)
and
not correlation was with QT dispersion.
CONCLUSION
Our
data suggest that QT dispersion on myocardial infarction patients on 10
day is
same than normal individuals and is greater only in 40% of
patients with severe ventricular arrhythmias.
No
correlation is between LP, F.E. and QT dispersion.
Althoug
furter studies must be done on larger patients popolation QT
dispersion appears poor
marker of ventricular arrhytmic risk in acute miocardial
infarction.
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