CV pharmacology 3: classes of drugs Flashcards
Class 4 antidysrhythmics
Block Ca2+ channels in Cardiomyocytes, nodal tissue and vascular smooth muscle
What affect to Class 4 antidysrhythmics have?
- vasodilation of vessels, relaxation of vascular smooth muscle
- Cardiomyocytes - Shorten plateau phase. (phase 2)
a) slows conduction in the SA and AV nodes
b) basically causing a partial AV block as cells with automaticity (pacemaker cells) have calcium dependent APs (pacemaker potential) - Acts as negative inotropes and lusiotropes – weaker contraction due to blockage Ca channels and vasodilation smooth muscle
When would we use Class 4 drugs?
- HyPERtension as good to reduce BP
- Hyper trophic cardiomyopathy (thick heart muscle) which leads to poor ventricular filling, high HR (common in cats).
a) Class 4 help slows HR down, allows to relax more, vasodilates, taking work off heart
Class 4 antidysrhythmics in practise e.g
Diltiazem (Hypercard)
When would you use Class 4 antidysrhythmics Diltiazem (Hypercard) in practise?
- Hypertrophic cardiomyopathy - muscle becomes abnormally thickened
- Diltiazem is a coronary and systemic vasodilator so improves perfusion of heart
Why is it important for patients with Hypertrophic cardiomyopathy to have dilated coronary arteries? What drug would you use?
- Class 4 antidysrhythmics Diltiazem (Hypercard)
- Diltiazem is a coronary and systemic vasodilator – improve perfusion of heart
- Coronary circulation fills during diastole. Systole it is squashed due to ventricular contraction.
- Hypertrophic cardiomyopathy = really fast HR, and thick muscle there is no time for vessels to fill, they’ll get even more squashed
How do you administer Class 4 antidysrhythmics Diltiazem (Hypercard)
- Oral and parenteral administration
- Sustained release preparations exist so don’t have to give regularly
- Initially have to give 3 times a day due to:
• Extensive first pass metabolism after oral administration = A lot doesn’t give metabolised
What would toxic levels of Class 4 (IV) antidysrhythmics
Diltiazem (Hypercard) result in
• Toxicity – negative inotrophy myocardial depression (no contraction), hypotension, AV block
Class 5 antidysrhythmics example and why so useful!
DIGOXIN (Lanoxin)
- USeful because the only negative chronotropy (dec HR) without being a negative inotropy!
- All other also reduce cardiac contractility! - and vagomimetic
When would we use the Class 5 antidysrhythmics Digoxin and why?
- Supraventricular tachycardia
- Digoxin is vagomimetic, it increases vagal outflow, enhancing action of the vagus nerve in the heart, mimicking the parasympathetic NS
- D slows conduction through AV node by increasing refractory period and allows longer filling time for V, thus improving cardiac output
Will Digoxin resolve the arrthythmia?
NOPE, doesn’t fix arrthythmia, just slows heart, so more time to fill
Why would digoxin be useful in atrial fibrilation
- In AF, AVNode is firing AP all over the place in atria
- chaotic irregular rhythm with no P waves, super fast
- so V can’t fill.
- seen often with advanced CHF adn dilated cardiomyopathy - stretched atria. D shows conduction through AV node, allowing V to have longer fillign time.
- Will improve CO
Adverse effects of lass 5 antidysrhythmics Digoxin
Has quite a lot but sometimes is the best option:
- Myocardial toxicity due to Intracellular calcium overload
- Arrhythmias due to development of automaticity and re-entrant rhythms (eptopic pacemakers)
- GI toxicity – often before myocardial toxicity develops
What is the difference between bradyarrhythmias and tachyarrhythmias
B = HR slower than normal T = heart rate higher than normal
What is an AV block?
type of heart block that occurs when the electrical signal traveling from the atria, or the upper chambers of the heart, to ventricles, or the lower chambers of the heart, is impaired.
It is the most common type of Bradyarrhythmia
