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Title: Influence of thyroid disturbances on QT corrected interval value and QT corrected interval dispersion

Abstract:

BACKGROUND. Electrocardiographic dispersion reflects the heterogeneity of ventricular re-polarization. It has been suggested that changes in QT dispersion in thyroid dysfunction can be a prognostic factor in different arrhythmias, especially ventricular arrhythmias. Calculations can be done from easily available tests such as: TSH serum level and resting electrocardiogram. AIM. The aim of the present study was to evaluate the prognostic value of the changes in thyroid dysfunction estimates of TSH, FT3, FT4 serum level and QT parameters (QTc, QTcd). I was looking for the answer concerning the correlation between these hormones and QTc and QTcd and whether QT parameters will be the prognostic factor for arrhythmias. METHODS. Out of 18 573 examined cardiology patients in years 2000-2005, a group of 516 was selected (2.77%) with thyroid dysfunction. The study group consists of 84 patients (0.45%) with isolated primary thyroid dysfunction in whom TSH, FT3, FT4 serum level was checked and resting electrocardiogram was made. There were 68 (81.0%) women and 16 (19.0%) men aged 27 to 78. The medium age was 54.7+-10.2 years old. The observation included patients with TSH level below 0.4 uU/ml or above 4.0 uU/ml in screening. It was confirmed by the FT3, FT4 serum levels. The results have been analyzed retrospectively in two groups: first (1)- with hyperthyroidism - 46 persons; 36 women (78.0%), 10 men (22%); second (2)-with hypothyroidism - 38 persons; 32 women (84%), 6 men (16%). Both groups were divided into two subgroups: A and B with low and high hyperthyroidism and hypothyroidism. RESULTS. In primary hyperthyroidic group (1A+1B) with TSH serum level below 0.4 uU/ml QT parameters increased. The relation seems to be inversely proportional. The lower ratio of TSH serum level, the higher the percentage of increasing distance between QTcd and QTc, especially in high level primary hyperthyroidic subgroup (1A) with TSH serum level below 0.1uU/ml. QTcd interval dispersion turned out to be a more sensitive parameter than the QT corrected interval. For QTcd>65 ms the sensitivity is 88.0%; the specificity is 42.9%. For QTc>448 ms the sensitivity is 60.0%; specificity is 71.4%. We also observed the proportional relation between free thyroid hormones (T3 , T4 ) and QT parameters ( QTcd , QTc). In primary hypothyroidic group (2A+2B) with TSH serum level above 4.0 uU/ml, we noticed that the QTcd parameter increased. For QTcd>65 ms the sensitivity is 66.7%; specificity is 20.0%. We did not observe any influence of high TSH serum level on extension of QTc parameter. For QTc>448 ms sensitivity is 44.0%; specificity is 40.0%. What is more, we did not observe statistical influence of lower ratio of FT3, FT4 on QTc in this group either. There was also no perceptible difference between the two hypothyroidic subgroups. CONCLUSIONS. 1/ In patients with primary hyperthyroidism occur extended QTcd and QTc values correlating with TSH serum level.2/ In primary hyperthyroidism a weak, directly proportional relationship between free hormones T3, T4 serum level and QTcd parameters have been found.3/ In primary hypothyroidism occurs only the relationship between TSH serum level and extended QTcd parameter.4/ QT corrected interval dispersion (QTcd) is a more sensitive index in patients with high primary hyperthyroidism level than QT corrected interval (QTc). In primary hypothyroidism only QT dispersion is a sensitive index. QT corrected interval (QTc) remained correct. 5/ Extension of QTcd and QTc parameters in high hyperthyroidism patients may betoken increased inclination to ventricular arrhythmias in this group of patients. 6/ Estimation of QT parameters makes up an easy noninvasive method of analyzing the reasons for arrhythmias in thyroid disturbances.

Level of degree:

2 - studia doktoranckie

Degree discipline:

choroby układu krążenia ; endokrynologia

Degree grantor:

Wydział Lekarski

Promoter:

Jacek S. Dubiel

Date issued:

2007

Format:

application/pdf

Identifier:

oai:dl.cm-uj.krakow.pl:1165

Call number:

ZB-106068

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tylko w bibliotece

Location of original object:

Biblioteka Medyczna Uniwersytetu Jagiellońskiego - Collegium Medicum

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Last modified:

Jun 25, 2019

In our library since:

Nov 21, 2012

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http://dl.cm-uj.krakow.pl:8080/publication/1165

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ZB-106068 Jun 25, 2019
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