What happens during a Threshold Test of Selective Placement?

During a Threshold Test of Selective Placement, the relationship between pacing output and the resulting QRS morphology is pivotal for understanding the efficiency and effectiveness of the pacing system.

The correct answer highlights that a higher pacing output may induce non-selective QRS morphology, which underscores the critical principle of selective versus non-selective pacing. Selective pacing refers to stimulating specific myocardial cells or structures to achieve an optimal physiological response or conduction pattern. When the output is increased beyond a certain threshold, it can lead to activation of additional myocardial fibers or pathways that were not intended to be stimulated, resulting in a change from a selective QRS morphology to a non-selective one. This emphasizes the importance of carefully adjusting the pacing output to maintain the desired selective conduction pattern for optimal cardiac function.

The significance of this dynamic is vital for clinicians when assessing pacing leads during implantation and testing, ensuring they achieve a selective stimulation that maximizes cardiac output without undesired effects on the QRS complex.