*4.1.4. Electrocardiogram*

In the early stage of the diagnosis process of MD, 12-lead electrocardiogram results are useful to add to the diagnostic criteria [146]. ECG results will be variable depending on the kinds of syndrome the mitochondrial myopathy is associated with [156]. Ocular myopathy patients may in general show normal ECG profile, but two out of the six patients were presented with ST depression and inverted T wave [156]. Patients with MELAS/MERRF may show atrial or ventricular premature contraction (APC or VPC) with T-wave abnormalities such as inverted T wave, as well as ST depression [156]. These abnormalities can be present even without the presentation of left ventricular hypertrophy [146]. A profile of short PR, or WPW, was also found for a MELAS patient [146, 156]. Patients with KSS presented cardiac conduction abnormalities with a variation of ECG profile of AV blocks, complete right bundle branch block with inverted T, or left axis deviation (LAD) and prolonged His ventricular (HV) interval [156]. Though some patients may show normal ECG profile at diagnosis, performing another ECG every 1–3 years may be important to detect uprise of cardiac abnormalities or complications [151].
