Antiarrhythmics

Question 1

How do class 2 work?

Answer 1

BB decrease SNS, so reduces the slope of phase 4

B receptors in nodal, conducting and myocardial tissue. Inhibits GPCR which decrease ca influx which decreases rate and contractility

Question 2

How do class 3 work?

Answer 2

Block K efflux which delays nodal and myocytes repolarisation. Increasing refractory period by decreasing slope of phase 3

Question 3

How do class 4 work?

Answer 3

Block L type Ca (widespread throughout CVS). Responsible for plateau phase,, so decrease slope of phase 0, decreasing rate. Also found in myocytes which decreases the contractility

Question 4

What are the differences between verapamil and nifedipine?

Answer 4

V = Racemic with L isomer having high affinity for L channels in nodes, so slow conduction . Less effect on contractility and vascular tone.

Nifedipine = little nodal effect, but marked decrease in arteriolar tone

Question 5

Tell me about adenosine?

Answer 5

Purine nucleoside used for termination of SVT or to differentiate between AF and flutter

Physical:
- CCS 3mg/ml
6/12/12
- large vein

PK:
A: 100%
D: t1/2 = 10s
M: deanimated in plasma and RBC

Pd:
MOA: binds to adenosine A1 receptor coupled with K channels, open and hyperpolarise. These are only found in nodes, so decreases conduction velocity
A: nil
B: bronchospasm in asthmatics. Sob and increased PVR
C: very stable but very transient Brady/pause
D: sense of impending doom,

Other: flushing and chest discomfort