ECG Flashcards
How does an atrial or ventricular muscle cell depolarise
+ve/-ve charge movement through gap junctions from previously depolarised cell
+ve charge flows through the gap junctions and depolarises the next cell
Sinus arrythmia
vagal activity is proportional to 1/HR
What is a 1st degree nodal block
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)
What is a 2nd degree nodal block
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)
What is a 3rd degree nodal block
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)
What is a Premature Ventricular Contraction
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
What sort of beat is PVC associated with
ECTOPIC
Diastolic interval after PVC is long
Compensatory pause allows for increased ventricular filling before next beat