Why is it significant to observe changes in surface EKG morphology during threshold testing?

Observing changes in surface EKG morphology during threshold testing is significant because it can signal misinterpretation and less optimal QRS complexes. When evaluating pacing thresholds, any substantial variation in the EKG morphology may indicate that the electrical signals are not being effectively conducted through the heart. This can lead to altered QRS complexes, which are crucial for assessing the heart's electrical activity and overall function.

An optimal QRS morphology is essential for ensuring that the pacing leads are in the correct position and that the heart is responding appropriately to the pacing impulses. If the morphology of the QRS changes, it may suggest issues with lead placement or electrode contact, or that the pacing is not uniformly stimulating the cardiac muscle. Such changes can ultimately affect the efficiency of pacing and the patient's overall cardiac performance.

In scenarios where the EKG morphology is compromised, clinicians may need to reassess lead placement, the type of pacing being used, or the threshold levels to ensure effective and appropriate cardiac stimulation.