Electrocardiogram showing<unk>  and irregular rhythm due to supraventricular extrasystoles. A<unk><unk>  is diagnosed on a 12-lead ECG. In adults, it is seen as wide QRS complexes lasting >120ms with characteristic QRS shapes in the precordial leads, although narrower complexes are seen in children. In lead V1, the QRS complex is often entirely negative (QS morphology), although a small initial R wave may be seen (rS morphology). In the lateral leads (I, aVL, V5-V6) the QRS complexes are usually predominantly positive with a slow upstroke last >60ms to the R-wave peak. Notching may be seen in these leads but this is not universal. The small Q-waves that are usually seen in the lateral leads are absent in<unk> . T-waves usually point in the opposite direction to the terminal portion of the preceding QRS - positive QRS complexes have negative T-waves while negative QRS complexes have positive T-waves. The ST segments typically slur into the T-wave and often appear elevated in leads with negative QRS complexes. The axis may be normal but may be deviated to the<unk>  or right. There are also partial<unk> s of the<unk><unk>  branch: "left anterior fascicular<unk> " (LAFB) and a "left posterior fascicular<unk> " (LPFB). This refers to the<unk>  after the bifurcation of the<unk><unk>  branch. Diagnostic consequences The presence of<unk>  results in that electrocardiography (ECG) cannot be used to diagnose<unk>  ventricular hypertrophy or Q wave infarction, because<unk>  in itself results in widened QRS complex, and changes in the ST segment consistent with ischemia or injury.
Left bundle branch block
Right bundle branch block
Bundle branch block
Sinoatrial block
Pre-excitation syndrome
Atrioventricular block
Sinoatrial arrest
Ventricular flutter