Premature ventricular contraction (PVC)

Question 1

What are causes of ectopic foci in premature ventricular contraction?

Answer 1

• Hypoxia
• Electrolyte abnormalities: K+, Ca2+
• Increased sympathetic nerve: increased EP, NE
• Stimulants: cocaine, ADHD
• Infarcted tissue (scar tissue): can cause reentrant circuits (when conduction travels around infarcted area)

Question 2

Answer 2

Rate = 90bpm (each QRS complex)
Rhythm
R-R: irregular
P wave: Some p waves
P–> QRS: AV dissociation
QRS: wide complex (more than 3 little boxes)

PVC happens after every 1 normal QRS complex –> ventricular bigeminy

PVC from irritable surface or reentrant circuit –> will not have normal conduction sequence (SAN–> AVN –> Bundle of His –> bundle branches –> purkinje fibers) hence no narrow QRS complex

Use leads to assess origin of PVC. As the QRS complex is negative in lead II it is likely at the left inferior ventricular portion going upwards away from lead II hence giving a negative deflection.

Question 3

Answer 3

Rate = 120bpm
Rhythm
R-R: irregular
P wave: present, but some abnormal
P–> QRS: AV dissociation
QRS: wide

Whenever a QRS complex comes early (look at R-R interval if earlier than others) –> it is a PVC

There is a PVC for every normal 2 QRS –> this is known as ventricular trigeminy

Question 4

Answer 4

Rate = 80bpm
Rhythm =
R-R: irregular
P wave: some p waves
P–> QRS: AV dissociation
QRS: wide qrs complex

3 beat salvo in this case

A PVC is normal.
When there is more than/including 3 continous PVCs –> it is pathological –> ventricular tachycardia
However if all the PVCs appearance look the same it is coming from the same ectopic foci