Arrythmia and AF Flashcards
What is the role of the SAN and where is it located?
Located in the RA near the opening of SVC. It is the pacemaker of the heart and starts depolarisation. It coordinates contraction of atria and sends impulses to the AVN.
What is the role of the AVN and where is it located?
Located in the RA near tricuspid valve on the inter-atrial septum. It acts as an electrical gatekeeper between atria and ventricles, by delaying impulse to ventricles allowing time for atria to contract and blood to fill the ventricles. Sends impulses to bundle of His.
What is the role of the His-purkinje fibres?
Spreads electrical impulses synchronously throughout RV and LV, allowing ventricles to contract at the same time.
What does the p wave indicate?
Atrial depolarisation.
What does the QRS complex indicate?
Ventricular depolarisation. Normal duration = 120 msec.
What does the T wave indicate?
Ventricular repolarisation.
What is the PR interval and what does it show?
Beginning of p wave to beginning of QRS complex. It shows the slow conduction through AVN. Time taken for atria to contract. Normal duration = 200 msec.
What is the QT interval and what does it show?
Beginning of QRS to end of T wave. It shows repolarisation of ventricles.
What is the ST segment and what does it show?
It is the isoelectric section of ECG between the end of S wave and beginning of T wave. It is the time between ventricular depolarisation and ventricular repolarisation.
What is normal resting HR, bradycardia and tachycardia?
Normal: 60-100bpm
Bradycardia: <60bpm
Tachycardia: >100bpm
What is the normal rate of PR interval and QRS complex?
PR interval: <200msec/<5 small squares.
QRS complex: <120msec/<3 small squares.
How many msec is one small square and one large square on ECG?
Small square: 40msec
Large square: 200msec
How would you calculate rate on ECG?
300/number of large squares between RR interval
OR
1500/number of small squares between RR interval
Define paroxysmal AF
Recurrent episodes (≥30 seconds in duration) that terminate spontaneously within 48 hours.
What are the 2 differentials for an irregularly irregular pulse?
Atrial fibrillation and ventricular ectopics.
How would you differentiate between AF and ventricular ectopics?
Using an ECG. Also, ventricular ectopics disappear over a certain HR threshold, therefore a regular HR during exercise suggests ventricular ectopics over AF.
Define valvular AF
Patients with AF who also have moderate or severe mitral stenosis or a mechanical heart valve.
Define non-valvular AF
AF without valve pathology or with other valve pathology such as mitral regurgitation or aortic stenosis.
Flecainide should be avoided in…
Atrial flutter
What is INR?
International normalised ratio. It’s a calculation of how the prothrombin time of the patient compares with the prothrombin time of a normal health adult. An INR of 1 indicates a normal prothrombin time. An INR of 2 indicates that the patient has a prothrombin time twice that of a normal healthy adult (it takes them twice as long to form a blood clot).
Describe the advantages of DOACs compared to warfarin
No monitoring is required.
No major interaction problems.
Equal or slightly better than warfarin at preventing strokes in AF.
Equal or slightly less risk of bleeding than warfarin.
Should aspirin be offered to prevent a stroke in a patient with AF?
No - there is no role for aspirin in preventing stoke in AF. This used to be recommended, but not any longer.
Describe the complications of AF (cardiac and non-cardiac)
Cardiac: HF, tachycardia-induced cardiomyopathy, ischaemia, sudden cardiac arrest.
Non-cardiac: thromboembolic events (stroke, TIA, mesenteric ischaemia, ischaemic limb), collapse, bleeding events (anticoagulation).
Describe some vagal manoeuvres
Valsalva manoeuvre - forced expiration against a closed glottis (covering mouth and nose).
Carotid sinus massage - massaging carotid artery for 5-10 secs whilst patient lying on back with head turned to one side.
Is it safe to prescribe non-dihydropyridine calcium channel blockers with beta blockers?
No as both classes are negatively inotropic and chronotropic, which together may cause HF, bradycardia and potentially asystole.
What are the 4 possible ECG rhythms in cardiac arrest?
VF, pulseless VT, pulseless electrical activity (PEA) and asystole.
How would you distinguish between SVT and VT?
Use adenosine as it blocks the AVN, therefore if it’s SVT the HR should slow.
Why are anti-arrhythmic drugs (e.g. beta blockers, calcium channel blockers, adenosine) contraindicated in patients with WPW syndrome that develop AF or atrial flutter?
Increased risk of causing a polymorphic wide complex tachycardia because anti-arrhythmic reduce conduction through AVN, promoting conduction through the accessory pathway. Increasing the risk that the chaotic atrial activity will pass through accessory pathway into ventricles.
Define bigeminy
Where ventricular ectopics are occurring so frequently that they happen after every sinus beat. The ECG looks like a normal sinus beat followed immediately by an ectopic, then a normal beat, then ectopic etc.
Define sick sinus syndrome
Aka sinus node dysfunction. It comprises a variety of disturbances affecting both generation of electrical activity from the sinus node and transmission within the atria. Examples include sinus bradycardia, sinus arrest/pause, tachy-brady syndrome.
Describe the antimuscarinic side effects of atropine
Pupil dilatation, urinary retention, dry eyes and constipation.
What is the most common arrhythmia?
Atrial fibrillation (AF).
Describe the pathophysiology of AF
Disorganised atrial electrical activity causes independent contraction of cardiomyocytes leading to fibrillation of the atria. Contraction of atria is uncoordinated, rapid and irregular.
Why does AF increase an individuals risk of ischaemic stroke?
Blood stasis in atria causes thrombus formation, which can lead to an embolism.
Name 5 causes of AF
Sepsis, mitral valve stenosis/regurgitation, IHD, thyrotoxicosis, hypertension.
What feature on examination would suggest AF?
Irregularly irregular pulse.
Describe the hallmark ECG features of AF
Irregularly irregular rhythm.
Absent p waves.
Irregular, fibrillating baseline.
Narrow QRS complex tachycardia.
Which scan is routinely requested in patients with new-onset AF?
Transthoracic echocardiogram.
What is the purpose of rate control in AF?
To allow the ventricles to fill with blood more efficiently.
What drugs can be used for rate control in AF?
Beta blockers, rate limiting calcium channel blockers (verapamil, diltiazem), digoxin.
How can rhythm control be achieved in AF?
Through cardioversion or long-term medication.
When would pharmacological cardioversion be indicated over electrical cardioversion in AF?
Pharmacological - AF presenting < 48 hours or severely haemodynamically unstable.
Electrical - AF presenting > 48 hours and stable.
How long must patients be anticoagulated for before electrical cardioversion?
3 weeks prior.
What drugs would be used for pharmacological cardioversion?
Flecainide or amiodarone (if patient has structural heart disease).
What is the first line medication for long term management of rhythm control in AF?
Beta blockers.
Describe the ‘pill in pocket approach’ for paroxysmal AF
Patient takes flecainide when they feel their symptoms starting. They must have infrequent episodes without any underlying structural heart disease.
What part of the heart does thrombus formation predominately occur in AF?
Left atrial appendage.
Describe the risks and benefits of anticoagulants
Slight increase bleeding risk. However bleeds are more reversible than strokes and have fewer long-term consequences. Benefits - it reduces stroke risk by 2/3.
What is the first line medication for anticoagulation in AF?
DOACs e.g. apixaban, rivaroxaban, dabigatran.
