Supraventricular ectopic beat is visible as narrow QRS complex without a preceding P wave (red arrow). PR interval of the sinus beats are at the upper limit of normal (200 ms). QR pattern (blue arrow) is seen in anterior leads, indicating old anterior wall infarction with right bundle branch block (QRBBB). This along with left anterior hemiblock (rS pattern in inferior leads) makes it an old anterior wall infarction with almost a trifascicular block.
50 Hz line voltage inference artefacts are seen as regular sine wave pattern of the baseline, especially in leads I, II, aVR and the anterior leads. To avoid such artefacts, meticulous attention has to be taken to reduce line voltage interference. Common sources are the ECG monitoring electrodes and the electrical connection of an electronically movable ICU cot. These electrical connections should be removed from their line output sockets. Good earthing of the electrical line is also useful. Switching on the 50 Hz notch filter in the ECG machine (line voltage filter) is also useful to some extent.