Arrhythmia Therapy Flashcards
What determines the resting membrane potential in the cardiac cells?
Uneven distribution of ions (Na, K, Ca) across membrane maintained but the Na-K ATPase pump
Produces a net negative charge inside the cells
What are the Vaughan-Williams classification of drugs used to treat arrhythmias?
Class 1: 1a, 1b, 1c Class II Class III Class IV Other or class V
What is the action of Class I drugs?
Stabilise membrane but vastly acting of Na channel blockers, slowing down rate of depolarisation
What are the different Class I drugs?
Ia: quinidine
Ib: lidocaine (weakest of the 3 in blocking)
Ic: flecanide - strong blocker
What is the action of Class II drugs?
Beta blockers - reduce or block the sympathetic NS and so reduce the transmission of impulses in heart
Act of phase 4 of action potential (resting potential)
What are example of BB drugs and their clinical use?
Atenolol
Bisoprolol
Propranolol
Genre myocardial depressant for SVT and V dysrhythmias
Bisoprolol is first line for AF
What is the actions of Class III drugs?
Increase the action potential duration by prolong depolarisation in phase 3
What are example of class III drugs and their clinical use?
Amiodarone
Bretylium
Sotalol
Used for hard to treat dysrhythmias
VT or VF, AF or flutter - resistant to other drugs
Sustain VT
What is the action of Class IV drugs?
CCB - slows the heart rate by depressing phase for depolarisation
What are example of CCB drugs and their clinical use?
Verapamil
Diltiazem
Paroxysmal SVT
Rate control for AF and flutter
Name other anti-dysrhythmic drugs
Digoxin
Adenosine
What type of drugs is digoxin?
Cardiac glycoside
What is the action of digoxin?
Inhibits the Na-K ATPase pump
Positive inotrope: improves the strengths of cardiac contraction by allowing more Ca to be available for contraction
What is the clinical use for digoxin?
Heart failure
Atrial fibrillation
But important to monitor K levels, drug levels and toxicity
Why can digoxin be toxic in patients with renal impairment?
Most of it is excretes by the kidneys, so in renal failure with reduced GFR, the half life is increase - so high conc. can remain in the body
What are side effects of digoxin toxicity?
Nausea and vomiting Xanthopsia (yellow in vision) Bradycardia Tachycardia Arrythmias: VT and VF
What is the sign of digoxin toxicity on an ECG?
Depression of ST segment in lateral leads
What is the treatment for digoxin toxicity?
Stop digoxin (still long half life so will stay in body after) If levels very high and risk of significant arrhythmia: give Digibind
What is the action of digibind?
Digoxin immune antibody - binds to digoxin, forming complex molecules which can be excreted in the urine
What is the clinical use of Amiodarone?
Used for VT and SVT
Many drug-drug interactions esp digoxin)
What are the side effects of amiodarone-drug interaction?
Hypo/hyper-thyroidism Pulmonary fibrosis Slate (grey pigmentation) Corneal deposits LFT abnormalities
What is the action of adenosine?
Slows the conduction through the AV node
Converts paroxysmal SVT to sinus rhythm
What is a side effect of the anti-dysrhythmic drugs?
ALL anti-arrhythmics can cause arrhythmias
What are indication for anticoagulation?
Atrial fibrillation (risk of stroke, peripheral emboli)
DVT/PE (for prophylaxis)
After surgery
Immobilisation (increased risk of DVT, given for prophylaxis)
Name 5 anticoagulants
Warfarin
Dabigatran
Riveroxaban
Apixaban
Edoxaban
What conditions may require anticoagulation?
Valvular heart disease
AF
Venous thromboembolism
Describe the arterial thrombosis
Andhere of platelets to arterial walls
White
Associated with MI, stroke, ischaemia
Describe venous thrombosis
Develops in areas of stagnated blood flow (DVT, L atrium)
Red
Associated with congestive heart failure
Cancer
Surgery
What is the action of warfarin?
Inhibits vit K metabolism which is required to produce clotting factors
What are mechanisms that will increase the activity of warfarin?
Decrease binding to albumin
Inhibit degradation
Decrease synthesis of clotting factors
What are mechanism that will decreased the activity of warfarin?
Indiction of metabolising enzymes (cytochrome P450)
Promote clotting factor synthesis
Reduce absorption
What is a way to monitor warfarin therapy?
Using International Normalised Ratio (INR) - to determine actual thromboplastin time (time taken for blood clots to form)
What are the values of INR?
Normal: 1
Therapeutic INR: 2.5-4 depending of clinical indication
What are the side effects to warfarin?
Bleeding
Teratogenic - avoid in 1st and 3rd trimester
What are 4 ways to monitor warfarin therapy?
Regular INR
Watch if therapy altered
Patient education
Alcohol intake
What are the benefits of Direct Oral Anticoagulants?
No required blood monitoring
No interaction with food or drugs
Given once/twice daily at fixed dose
As effective and safer than warfarin
What are 4 different DOAC and their actions?
Direct thrombin inhibitor: Dabigatran and Apixaban
Factor Xa inhibitor (prevents formation of thrombin): Rivaoxaban and Edoxaban
