Expert: Walter Hintz - 1/22/2010

Question
I am struggling to understand why the statement below is true. My thoughts so far have been that they many contain different amounts of ion channels to let ions in/out. But I know that pacemaker cells have electrical impulses that give the rhythm of the heart but do ventricular muscle cells not go by the rhythm set by those of the pacemaker cells?

'Action potentials recorded by from the cardiac pacemaker cells differ from those of the ventricular muscle cell.'

Many thanks

Tasha  

Answer
Hi Tasha
The rhythm of the ventricle is only manifest if there is  failure of the SA and AV nodes.
Since the SA node (pacemaker) is generating impulses of 70-80 per minute impulses from the ventricle are not generated.  The ventricular rate is about 25 per minute.  The AV node also has a potential of about 60 per minute.  If the SA node fails the heart rate would be regulated by the AV node. In case of a bundle branch bloch the ventricular rate of 25 per minute would then pick up the pace.
I hope this answers your question.
walter