ECG basics (1.7). Transition point

Описание: In a normal heart, the R-wave amplitude increases from lead V1 to lead V5 (or V6). The S-wave amplitude decreases from lead V1 (or V2) to lead V5 (or V6). Normally, the R- and S-wave amplitudes are equal in lead V3 or V4. This is called the 'transition point' or 'transition zone'.
The transition point may shift toward leads V5-V6. This is called clockwise rotation. This condition is often seen in pulmonary emphysema, dilated cardiomyopathy, and intraventricular conduction abnormalities.
The transition point may shift toward the V1-V2 leads. This condition is called counterclockwise rotation. It can be observed in right ventricular hypertrophy, posterior myocardial infarction, WPW syndrome, and hypertrophic cardiomyopathy.
In the case of clockwise rotation, the deep S-wave in lead V6 is called 'persistent'.
Normal R-wave progression in the precordial leads is of great importance. Poor R-wave progression may be the only sign of anterior myocardial infarction. In this case, the R-wave amplitude is low in the leads from V1 to V3 (often in the leads from V1 to V4). Some authors define this condition by R-wave height less than 3 mm in lead V3. Other important causes of poor R-wave progression include lead misplacement, dextrocardia, mediastinal shift, left ventricular hypertrophy, and dilated cardiomyopathy.