Which lead is instrumental for observing selective and non-selective captures?

Lead II is instrumental for observing selective and non-selective captures because it aligns closely with the normal cardiac electrical axis, allowing for enhanced visibility and assessment of atrial and ventricular captures during pacing. This lead provides a comprehensive view of the heart's electrical activity, particularly in a horizontal plane, which is essential for differentiating between the types of captures.

Selective capture occurs when pacing successfully stimulates only the intended chamber, allowing more precise control and optimization of pacing parameters. Non-selective capture, on the other hand, implies that additional myocardial cells are also being stimulated, which could lead to unintended effects such as fusion beats or varying cardiac output.

The ability of Lead II to clearly display these phenomena is due to its orientation and the fact that it encompasses the flow of electrical impulses moving from the atria through the ventricles. This characteristic makes it a preferred lead in various pacing scenarios, aiding clinicians in identifying and troubleshooting capture issues effectively.

Other leads, while useful, may not provide the same clarity or accuracy in assessing capture types like Lead II does, making it the most reliable choice for this specific measurement in conduction system pacing.