What might happen to cardiac output if a higher number of QRS complexes are blocked in a second-degree type 2 AV block?

In a second-degree type 2 AV block, there is a consistent failure of some of the impulses to be conducted from the atria to the ventricles, resulting in dropped QRS complexes. This disruption in the conduction system means that not every atrial contraction will lead to a corresponding ventricular contraction. As more QRS complexes are blocked, the effectiveness of the heart's pumping action can be significantly reduced.

Cardiac output, defined as the volume of blood the heart pumps per minute, depends on both the heart rate and the stroke volume (the amount of blood ejected with each heartbeat). When QRS complexes are blocked, the heart rate decreases because fewer impulses are reaching the ventricles, leading to fewer contractions. Additionally, if the contractions that do occur are not coordinated or efficient due to the irregular rhythm caused by the block, stroke volume can also decrease.

Therefore, as the number of blocked QRS complexes increases in this condition, the overall cardiac output will likely decrease due to a reduced heart rate and possibly impaired stroke volume. This cellular and mechanical dysfunction within the heart results in a compromised ability to deliver adequate blood flow to meet the body's demands, especially during times of increased activity or stress.