Pharmacology of rhythm control Flashcards
Phases of the cardiac myocyte AP:
4 0 1 2 3
Phase 4 =
Resting membrane potential, K+ open
Phase 0 =
Rapid depolarisation, Na+ open
Phase 1 =
K+ open, small repolarisation
Phase 2 =
Plateau phase. K+ and Ca2+ open
Phase 3 =
Repolarisation. K+ open.
ERP =
Effective refractory period
Phases of nodal AP =
4
0
3
Can tetanus occur in cardiac myocytes?
No
RRP
Relative refractory period.
When can cardioversion cause VF?
If shocked during relative refractory period.
Phase 4 (nodal) =
T-type Ca2+ and Na+ open
Phase 0 nodal =
L-type Ca2+ channels
Phase 3 nodal =
voltage gated K+ open
Intrinsic rate of SAN
60-100 bpm
Intrinsic rate of AVN
40 bpm
What is the HR in complete heart block?
40 bpm
Where is the SAN?
Junction of SVC and RA
Where is the AV node?
Inter-atrial septum
What part of the heart conducts the fastest?
His-purkinje system
Conduction rate of His-purkinje system
2-3 m/sec
Conduction rate of ventricular and atrial muscles
1 m/sec
Which part of the heart conducts the slowest?
AVN
Conduction velocity of AVN
0.05 m/sec
Which kind of heart block is asymptomatic?
Type 1
Mobitz I
Treatment of Mobitz 2
Close monitoring
Pacing
Why is monitoring of mobitz 2 important
Can progress to complete heart block
Treatment of complete heart block =
Atropine
Isoprenaline
Pacing
Symptoms of 2nd and 3rd degree heart block =
Dizziness Syncope SOB Pain Fatigue
Atrial rate in atrial flutter is usually =
300/min
What can be given to see atrial flutter?
Adenosine
Torsdaes de pointes is a type of
Ventricular tachycardia
Causes of trosades de pointes =
- Congenital long QT
- Heart block/bradycardia
- Hypokalaemia or hypomagnaemia
- Drugs (Type III antiarrthymics)
Treatment of Vfib =
Direct current shock
How to manage arrthymias:
- Treat causes
- Vagotonic manoeuvres
- DC cardioversion
- Pacing
- Surgery/ablation
- Drugs
How to treat bradycardia due to beta-blocker OD
Glucagon
How to treat bradycardia due to Ca2+ blocker OD
Glucagon
How to treat bradycardia due to acute digoxin toxicity
Digoxin-specific antibodies
Ca2+ blocker
MoA atropine =
Antimuscarinic
What to not give to cardiac transplant patient
Atropine
If atropine fails, how should you treat bradycardia?
External pacing
Hs and Ts describe =
Reversible causes of cardiac death
Hs + Ts =
Hypovolemia Hypothermia Hypo/Hyperkalaemia Hypoxia Throbosis Toxins Tension pneumothorax Cardiac tamponade
name a classification of antiarrthymics =
Vaughan Williams
Class I
Na+ blockers
Class II
Beta blockers
Class III
K+ blockers
Class IV
Ca2+ blockers
MoA of Na+ blockers
Increase duration of depolarisation
MoA of betablockers
Reduce sympathetic activity on SAN
MoA of K+ blockers
Prolong repolarisation
MoA of Ca2+ blockers
Prolong refractory period (nodal)
Disopyramide
Na+ blockers
Lidocaine
Na+ blockers
Flecainide
Na+ blockers
Antenolol
beta blockers
Amiodarone
K+ blocker
Verapamil
Ca2+ blocker
Diltiazem
Ca2+ blocker
MoA of adenosine
K+ channel activation - slows conduction through AV
Use of adenosine
SVT
MoA of digoxin
K+, Na+ ATPase inhibition
Uses of digoxin =
AF
Atrial flutter
CHF
What is digoxins ionotrophic effect?
+ve ionotrophy
Low therapeutic index =
Dosing between therapeutic and lethal dose narrow
What should you reduce digoxin dose in?
Elderly
Renal impairment
Hypokalaemia, hypomagnesia, hyperclacaemia
Side effects of digoxin =
- Arrythmias, AF
- GI
- Blurring of vision
- Gynaecomastia
- CNS effects
First line drug in ICU for SVT and VT =
Amiodarone
Side effects of amiodarone
- Bradycardia, heart block, arrhythmia
- Hypo/hyper thyroidism
- Photosensitivity
- Blue-grey skin
- Lung fibrosis
- Abnormal LFTs
Why can amiodarone cause hyper/hypothyroidism
Contains iodine
What is used in VT when amiodarne is contraindicated?
Lidocaine
Class of lidocaine =
Class ib
Contraindications of Ca2+ blockers =
Pregnancy
Cardiogenic shock
Severe bradycardia
Heart failure