ECG

Question 1

How does an atrial or ventricular muscle cell depolarise

Answer 1

+ve/-ve charge movement through gap junctions from previously depolarised cell
+ve charge flows through the gap junctions and depolarises the next cell

Question 2

Sinus arrythmia

Answer 2

vagal activity is proportional to 1/HR

Question 3

What is a 1st degree nodal block

Answer 3

If the conduction velocity through the AV node is slowed due to injury, PR interval will be lengthened (> 0.2s, as normal is 0.12-0.2s)

Question 4

What is a 2nd degree nodal block

Answer 4

If AV node conducts only some of the supra-ventricular depolarisations => not all P waves will be followed by QRS complexes (3:2 or 2:1)

Question 5

What is a 3rd degree nodal block

Answer 5

Complete electrical block between atria and ventricles
AV nodes fail to conduct any signals
P wave occurs regularly
QRS waves occur but with decreased force (secondary pacemaker)

Question 6

What is a Premature Ventricular Contraction

Answer 6

Heartbeat normally originates within the atria @ SA node but in abnormal situations (e.g. acute myocardial ischaemia) heart beat may originate in ventricle
PVC not preceded by P wave as the origin is VENTRICULAR

Question 7

What sort of beat is PVC associated with

Answer 7

ECTOPIC
Diastolic interval after PVC is long
Compensatory pause allows for increased ventricular filling before next beat