Question

1. During atrial fibrillation, what would be the result if all of the electrical impulses from the atria were conducted through the AV node to the ventricles? How would it affect stroke volume? Cardiac output?

Answer 1

Atrial fibrillation is a pathological supraventricular tachycardia_Here atrial fibres are activated asynchronously at a rate of 350-550/min(due to elecrtophysiological inhomogenicity of atrial fibres).Also associated with grossly irregular and often fast (100-160/min)ventricular response.Atria remains dilated and quiver like a bag of worms.

In normal heart SAN produces major impulses which travels to ventricles via AVN and bundle of his.

AVN is specialized in slow conduction.Any impulse which is passed to ventricles should pass via AVN.In atrial fibrillations all impulses produced in SAN are not transmitted to Ventricles.So ventricular contractions are lesser than atrial contraction rate.If all the impulses are passed to ventricles,Changes will be_ heart rate will increase,stroke volume will decrease,cardiac output will ddcrease.

Reason_ventricular diastole time is more than systole time like that in atria.ventricle gets filled with blood from atria during diastolic phase(atrial systole coincides with ventricular diastole).If heart rate will increase,diastolic time will decrease,ventricles cant fill with blood properly,which will decrease end diastolic volume_This will affect stroke volume_decreased.

Though heart rate increased,ventricles cannot pump much blood so(stroke volume decreased) so cardiac output will decrease eventually.

Also coronary blood flow occours during diastole.Diastole phase decreased_coronary blood flow decreased but the demand increased due to increased heart rate leading to angina like symptoms_chest pain,shortness of breath