Modified limb lead system: Its effects on wave amplitudes and axis in surface ECG

Modified limb lead (MLL) electrocardiogram (ECG) system may be used during rest or exercise ECG test, or in atrial activity enhancement. Due to modifications to limb electrode placement, changes are likely to happen in ECG wave amplitudes and frontal plane axis, which may alter the clinical limits of normality and ECG diagnostic criteria (1). There are also several other alternative lead systems that are placed on the human torso to record and study the electrical activity of the atria (2–4). A few recent studies have proposed modification to the standard 12-lead ECG system of placing the limb electrodes closer to the atria in order to enhance atrial ECG components (5–7).