[Fundamentals of 12-lead electrocardiography in intensive care medicine]

The surface electrocardiogram (ECG) is an important diagnostic tool for the diagnosis of arrhythmias and acute coronary syndrome. Arrhythmias are divided into bradycardias (heart rate < 50/min) and tachycardias (heart rate > 100/min). Among tachycardias, differentiation between small QRS complexes (QRS width < 0.12 s) and broad QRS compexes (≥ 0.12 s) during tachycardia is necessary. It is important to analyze the relationship between P wave and QRS complex, to look for an electric alternans as a leading finding for an accessory pathway. Wide QRS complex tachycardias (QRS width ≥ 0.12 s) occur in supraventricular tachycardias (SVT) with aberrant conduction, SVT with bundle branch block or ventricular tachycardia (VT). In broad complex tachycardias, atrioventricular (AV) dissociation, negative or positive concordant pattern in V1-V6, a notch in V1, and qR complexes in V6 in tachycardias with left bundle branch block morphologies are findings indicating VT. In addition, an R/S relationship < 1 in V6 favors VT when right bundle branch block tachycardia morphologies are present. By correctly analyzing the surface ECG with a systematic approach, the specificity and sensitivity of correctly identifying a SVT or VT can be increased to greater than 95 %. The12-lead surface ECG is an important diagnostic tool for intensive care medicine. However, good ECG knowledge and systematic analysis are necessary to make the right diagnosis.