heart doctors in Kattigenahalli, Bangalore • Impulse conduction Sinoatrial block Some instances of apparent sinus bradycardia are due to sinoatrial (SA) block; this can be ascertained only by observing variations in conduction ratios or characteristic periodicity, The sinoatrial node beats (yes, beats) continuously, 7 but some impulses are blocked from entering the atria. The pauses are often termed ‘sinoatrial block’ or ‘sinus arrest’; it is probably permissible to call them ‘sinus pauses’ for convenience. The upper strip shows typical Wenckebach (see below) grouping, with slight acceleration in the last two groups prior to pauses that themselves are shorter than two sinus cycles. The most likely interpretation is 3:2 and 4:3 SA exit block in this patient with known sick sinus syndrome . The lower strip, taken later, shows only sinus arrhythmia (waxing and waning of the sinus rate with respiration—a normal occurrence). Interatrial block The term LAA, of which abnormal interatrial conduction (block) is a major cause, has replaced the more elegant term P mitrale because mitral valve disease is only one cause of the condition. The P wave is prolonged to or beyond 0.10 seconds and is often notched ); the significant notching should have an inter-peak distance of at least 1 mm (0.04 seconds). It is thought to represent a lesion in Bachman’s bundle, the interatrial tract. Atrioventricular blocks Atrioventricular (AV) blocks delay (first-degree) or prevent some (second-degree) or all (third-degree) of the supraventricular impulses from reaching the ventricles. The blocks may be congenital or acquired, transient or permanent. The most clinically useful classification is based on their anatomical cause and their ECG manifestations. This classification also helps in