Step I Beta 1 Blocker Effect on SV

[PagingDr.F]

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Beta 1 blockers will decrease heart rate and contractility. Would this decrease in heart rate allow for an increase in ventricular filling time and therefore, a larger stroke volume? Or would SV decrease because of the decreased contractility?

Basically, I'm having a hard time figuring out which factor (preload vs contractility) has a greater influence on the stroke volume.

 

[wanderingorion]

Beta 1 blockers will decrease heart rate and contractility. Would this decrease in heart rate allow for an increase in ventricular filling time and therefore, a larger stroke volume? Or would SV decrease because of the decreased contractility?

Basically, I'm having a hard time figuring out which factor (preload vs contractility) has a greater influence on the stroke volume.

To maintain cardiac output, SV must increase to compensate for decreased HR due to decreased sympathetic activity. Contractility is increased by sympathetic input, but I think it's primarily a product of EDV, so decreased HR would increased EDV (by increased filling time like you said).