Date Published: December , 2017
Publisher: Makerere Medical School
Author(s): Ogba J Ukpabi, Basden JC Onwubere.
Prolonged corrected QT (QTc) has been identified as a risk factor for malignant arrhythmias and sudden cardiac death. Caucasian studies have shown a definite relationship between QTc prolongation and Cardiac Autonomic Neuropathy (CAN) in diabetic subjects.
To determine the prevalence of prolonged QTc in Black diabetic individuals with CAN and to ascertain how prolonged QTc correlated with the severity of CAN among these patients.
A total of 176 adult diabetic subjects were studied, 87 males and 89 females. There was a control group of non-diabetic individuals. Cardiac autonomic function was assessed using five cardiovascular autonomic function tests. CAN was diagnosed if 2 or more of these tests were abnormal. Severity of CAN was determined according to the number of abnormal tests. QTc > 0.440 was regarded as prolonged.
Fifty-one out of the 176 diabetic subjects (29%) had CAN. The prevalence of prolonged QTc in diabetic subjects with CAN was 12%. QTc was prolonged in 1.6% and 0.6% of diabetic individuals without CAN and controls respectively. Although QTc correlated strongly with cardiac autonomic function neuropathy, there was no definite relationship between QTc prolongation and severity of CAN.
This study in a Black population is in agreement with the well-known relationship between QTc prolongation and CAN reported in Caucasian studies. In view of the wide variability of QTc in this study population, it is suggested that relative QTc increase may be a better indicator of CAN than a definite QTc prolongation of greater than 0.440.
Sudden death is probably the greatest challenge facing modern cardiology by virtue of the dramatic nature of its presentation and the number of victims claimed. Cardiac autonomic neuropathy has been identified as one of the factors predisposing to sudden cardiac death.1–3 It results from the dysfunction of the parasympathetic (vagal) or sympathetic supply to the heart or both.4,5 Autonomic cardiac neuropathy is a recognized complication in a number of diseases including diabetes mellitus.6 Neuropathy has been reported as the commonest chronic complication of diabetes mellitus, a disease that has been described in all races.7 Pop-Bussi et al8 reported that the prevalence of diabetic Cardiac Autonomic Neuropathy ranges from as low as 2.5% to as high as 90%. In the late 1970s, a high incidence of sudden death was reported in diabetic patients who had autonomic neuropathy.9,10 Cardio-respiratory arrest was identified as the cause of death in some cases but in the overwhelming majority the cause of death was not identified. Studies done in the 1980s showed significantly prolonged QT in diabetic patients with cardiac autonomic neuropathy.1,2 Later researchers confirmed this.11–16 The prevalence of prolonged corrected QT (QTc) in diabetic individuals with cardiac autonomic neuropathy varies from 6% to 70.5% in Caucasian studies.1–16–19 Prolonged QT has also been found in cardiac autonomic dysfunction due to other causes.20 An association between prolonged QT interval and sudden cardiac death has been found in various diseases.21,22
The study was done at the University of Nigeria Teaching Hospital Enugu, a designated centre of excellence for cardiovascular disease in Nigeria. Ethical clearance was obtained from the research ethical committee of this hospital and informed consent obtained from the subjects.
The data obtained in the study was analyzed with Statistical Package for Social Sciences (SPSS) 9.0, Dbase IV and Microsoft Excel. The mean values of the QTc were compared between groups using the student’s ‘t’ test. The standard deviation (SD) of the QTc within each group was determined and used to assess the variability of the results within each group. The proportions of prolonged QTc in the various groups were compared with Chi square statistic. Correlation among variables was tested by Pearson correlation for parametric variables. Regression analysis was performed with QTc as the dependent variable to reveal the relationship between QTc and cardiac autonomic function score, age of subject and duration of diabetes. Differences in results were regarded as statistically significant when p<0.05. One hundred and seventy-six diabetic patients who met the inclusion criteria were recruited. There were 87 males and 89 females. Their ages ranged from 18 to 60 years with mean age of 46.09 ± 9.51. Their ages were matched for sex and age with 176 controls. Out of the 176 diabetic patients, 148 (84.1%) were non-insulin dependent diabetics (NIDDM) [mostly type 2] and 28 (15.9%) were insulin dependent diabetics (IDDM) [these were patients who required insulin from the onset (type 1) or required insulin following oral hypoglycaemic agents failure (type 1½)30,31. The diagnosis and assessment of severity of cardiac autonomic neuropathy was done using cardiovascular autonomic reflexes as is widely used in clinical practice and research.15,17,28,29 The use of radio-labelled analogs of norepinephrine in evaluating CAN though more direct and specific is too expensive for routine clinical assessment especially in developing countries.32 There is a definite prolongation of QTc in Black diabetics with CAN in agreement with the well-known relationship between QTc prolongation and CAN. The prevalence of QTc in Diabetic Cardiac Autonomic Neuropathy in this study (12%) falls within the range obtained in Caucasian studies. Source: http://doi.org/10.4314/ahs.v17i4.17