If the signal from the SA node to the AV node is blocked or delayed, what variable directly changes?

The SA node sets the rhythm of your pulse and the AV node sets the rhythm of your heart contractions.

While the SA node sets the rhythm of your pulse, the AV node sets the rhythm of your heart contractions. It delays the signal on its way to the ventricle, giving the atrium time to contract first. It holds it up for about a tenth of a second. If the atrium and the ventricle contracted at the same time, the ventricles would push out their blood before they were totally full, resulting in low blood pressure, among other problems.

so is the answer a ?