In a second-degree type 2 AV block, what factor influences patient symptoms?

In a second-degree type 2 AV block, the factor that most significantly influences patient symptoms is indeed the number of QRS complexes that are not conducted. This type of AV block is characterized by a progressive failure of some atrial impulses to be transmitted to the ventricles, resulting in missing QRS complexes. The severity of symptoms can correlate directly to how many of these impulses are being conducted effectively. If a considerable number of P waves lead to non-conducted QRS complexes, the heart will not be able to pump adequately, potentially leading to symptoms such as weakness, dizziness, or even syncope due to reduced cardiac output.

While the other factors listed—such as the duration of the P-R interval, the patient's age and fitness level, and the presence of coexisting cardiovascular conditions—may contribute to the clinical picture or overall risk profile, they do not directly influence the number of conducted versus non-conducted impulses. Therefore, assessing the frequency of QRS complexes that are conducted is critical in understanding the patient's symptoms and ensuring appropriate management in cases of second-degree type 2 AV block.