Research Article: The Association between Myocardial Iron Load and Ventricular Repolarization Parameters in Asymptomatic Beta-Thalassemia Patients

Date Published: May 15, 2012

Publisher: Hindawi Publishing Corporation

Author(s): Mehmet Kayrak, Kadir Acar, Enes Elvin Gul, Orhan Özbek, Turyan Abdulhalikov, Osman Sonmez, Hajrudin Alibaşiç.

http://doi.org/10.1155/2012/170510

Abstract

Previous studies have demonstrated impaired ventricular repolarization in patients with β-TM. However, the effect of iron overload with cardiac T2* magnetic resonance imaging (MRI) on cardiac repolarization remains unclear yet. We aimed to examine relationship between repolarization parameters and iron loading using cardiac T2* MRI in asymptomatic β-TM patients. Twenty-two β-TM patients and 22 age- and gender-matched healthy controls were enrolled to the study. From the 12-lead surface electrocardiography, regional and transmyocardial repolarization parameters were evaluated manually by two experienced cardiologists. All patients were also undergone MRI for cardiac T2* evaluation. Cardiac T2* score <20 msec was considered as iron overload status. Of the QT parameters, QT duration, corrected QT interval, and QT peak duration were significantly longer in the β-TM group compared to the healthy controls. Tp − Te and Tp − Te dispersions were also significantly prolonged in β-TM group compared to healthy controls. (Tp − Te)/QT was similar between groups. There was no correlation between repolarization parameters and cardiac T2* MRI values. In conclusion, although repolarization parameters were prolonged in asymptomatic β-TM patients compared with control, we could not find any relation between ECG findings and cardiac iron load.

Partial Text

Beta-thalassemia major (β-TM) is a hereditary hemogolinopathy caused by impaired synthesis of β-globin chain and requires frequent blood transfusions [1]. In a consequence of transfusions, iron overload may develop. Deposition of iron in the heart may occur and cause severe cardiac complications such as heart failure and malignant arrhythmias [2]. The incidence of iron overload cardiomyopathy ranges from 11.4 to 15.1% in β-TM patients [3, 4]. Despite advances in chelating therapy, cardiovascular complications still remain main cause of mortality and morbidity in patients with β-TM [4].

Table 1 summarizes the clinical, laboratory, and echocardiographic characteristics of the study population. β-TM patients were not different from the control group in age, gender, body-mass index, or blood pressure levels. The mean cardiac T2* value of patients with β-TM was 21.7 ± 9.0 ms. Hemoglobin (Hb) and hematocrit (Hct) levels were significantly lower in β-TM group than in the control group (Table 1). Heart rate was significantly increased in β-TM patients than controls (85 ± 8 bpm versus 78 ± 7 bpm, P = 0.004) (Table 1). Mean cardiac T2* MRI value was  23 ± 16 msec.

The present study demonstrated that repolarization parameters including QT, QTc, QTp, Tp − Te, and (Tp − Te)d were significantly prolonged in patients with β-TM compared to healthy subjects. Neither conventional QT parameters nor transmyocardial repolarization parameters were correlated with cardiac T2* MRI values. To the best of our knowledge, the present study is a first time study, where the relation between cardiac T2* MRI values and transmyocardial repolarization parameters was investigated.

A few limitations deserve mention: (a) this study is a cross-sectional study with small sample size and large prospective randomized studies are needed to clarify the relationship between the both impaired regional and transmyocardial repolarization parameters and subsequent cardiac events in β-TM patients, (b) we did not perform cardiac MRI in control group because of cost. In addition, because of controversial results in the literature, we aimed to evaluate whether repolarization parameters are impaired in patients with β-TM or not, (c) β-TM patients were under chelation therapy and this type of therapy may blind results of the study. Therefore our results may not be applicable to patients not undergoing this kind of therapy, (d) because of speculations that fibrosis as a cause of iron load may impair repolarization parameters, we think that investigation of noninvasive markers of fibrosis, such as metalloproteinase, procollagen type I, and procollagen type III needs to be investigated in future.

The present study demonstrated that repolarization parameters are impaired in asymptomatic β-TM patients and it was unrelated with cardiac T2* MRI values. Thus it needs to well-designed randomized investigations in this area.

 

Source:

http://doi.org/10.1155/2012/170510

 

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