Cardio - AF Flashcards
what is the prevalence of AF in adults?
3% (more common in males and in older people) - most common sustained cardiac arrhythmia
what is AF? describe the rhythm it produces
- Chaotic asynchronous electrical activity in atrial tissue as a result of impulse firing from multiple re-entry circuits.
- Results in irregularly irregular rhythm, with rate depending on degree of AV block
what is the heart rate in AF usually? what is the difference between controlled and uncontrolled AF?
Depends on degree of AV block.
- atrial rate is indiscernible but often >400 bpm
- ventricular rate usually 100-150 bpm. AF considered controlled if ventricular rate <100 bpm, and uncontrolled if rate >100 bpm
name common causes of AF
- coronary heart disease, inc. MI
- HTN
- valvular heart disease
- hyperthyroidism
- lone AF (no obvious cause) - 11%
what are the downstream negative consequences of AF?
Loss of atrial kick and decreased diastolic filling time (due to rapid HR)… loss of active ventricular filling (decreased end-diastolic volume by about 20%):
i) significant decrease in CO (esp. during exercise)… heart failure (may be severe if pt also has cardiac disease), MI or syncope if AF is uncontrolled
ii) stagnation of blood in atria… thrombus formation and risk of embolism (stroke and PE)
what is the difference between acute, paroxysmal, recurrent, persistent and permanent AF?
- acute = onset within prev. 48hrs
- paroxysmal = spontaneous termination within 7 days, most often within 48hrs. May degenerate into sustained form of AF.
- recurrent = 2+ episodes which may be defined as paroxysmal if terminate spontaneously.
- peristent = not self-terminating, lasting >7 days or prior cardioversion, requires electrical or pharmacological cardioversion for termination.
- permanent = long-standing AF (>1 yr) that is not successfully terminated by cardioversion, when cardioversion is not pursued or has relapsed following termination (reversion to sinus rhythm is still possible)
Name common causes of new-onset AF or worsening of pre-exiting AF.
PIRATES:
- PE
- Ischaemia
- Respiratory disease, e.g. pneumonia
- Atrial enlargement or myxoma
- Thyroid disease
- Ethanol
- Sepsis / Sleep apnoea
These pts may require emergency management.
Describe the possible symptoms of AF.
Caused by decreased CO:
- dyspnoea
- palpitations
- syncope/dizziness
- chest discomfort
In cases of chronic AF, heart may be able to compensate for decreased CO, with pts becoming asymptomatic (although at increased risk of embolism).
Which signs may be detectable in a pt with HF?
- irregularly irregular pulse (+/- abnormal HR)
- radial pulse rate slower than apical pulse rate (each ventricular contraction not necessarily strong enough to transmit an aterial pulse wave)
- hypotension (if haemodynamically unstable, due to decreased CO)
which investigations would you perform on a pt with AF?
Assessment focused on identifying any underlying cause, and assessment of cardiac function.
- Bloods
- FBC: anaemia may precipitate HF
- U&Es: abnormal serum K+ can potentiate arrhythmias
- TFTs: screen for hyperthyroidism
- LFTs
- troponin: if Hx of chest pain
- coagulation screen: pre-anticoagulation treatment (e.g. warfarin) - Bedside tests
- ECG: diagnostic, exc. in paroxysmal AF between attacks (use 24hr ambulatory ECG monitor or event-recorder ECG) - Imaging
- CXR: may indicate cardiac structural causes of AF, e.g. mitral valve disease or HF
- TTE: performed in pts with AF for whom baseline echo important for long-term management, in whom cardioversion is considered or in whom there is suspicion of underlying structural/functional heart disease that influences subsequent management
- brain CT/MRI: if any suggestion of stroke or TIA
describe the ECG features seen in AF
- rhythm: atrial and ventricular are irregularly irregular
- rate: atrial >400 bpm, ventricular 100-150 bpm
- P wave: absent, may have baseline fibrillatory (f) waves
- PR interval: indiscernible
- QRS complex: usually normal
- T wave: indiscernible
- QT interval: not measurable
how would you manage a pt presenting with unstable AF?
Rare, requires urgent senior input due to haemodynamic instability (systolic BP <100) for rapid restoration to sinus rhythm via cardioversion (without delaying to achieve anticoagulation):
- A-E management
- start rare and rhythm control if onset <48 hrs
- pharmacological cardioversion (75% success rate): FLEICANIDE or AMIODARONE if no evidence of structural or coronary heart disease, or amiodarone if evidence of structural disease
- electrical cardioversion (90% success rate): a TEE may be obtained before EC to rule out thrombi in the atria (or resumption of normal contractions can result in systemic emboli) - start rate control only if onset >48hrs or uncertain (cardioversion contra-indicated due to high risk of thromboembolism). Delay cardioversion until they have been maintained on therapeutic anticoagulation for min. 3 wks.
how would you manage a pt presenting with stable AF?
Interventions aim to decrease ventricular response rate to <100 bpm, establish anticoagulation and restore and maintain a sinus rhythm.
- decrease ventricular response: B-blockers (e.g. PROPANOLOL, METOPROLOL, ATENOLOL) or CCBs (DILTIAZEM, VERAPAMIL). Pts with decreased LV function typically receive DIGOXIN.
- anti-coagulation (crucial to reduce risk of thromboembolism): WARFARIN and HEPARIN used for anti-coagulation and to prepare pt for elective cardioversion.
- rhythm control: may be considered although most pts relapse within 1 yr and it doesn’t provide a survival benefit compared with rate control.
- ablation therapy (microwave catheter ablation, thorascopic epicardial radiofrequency ablation) should be considered in all symptomatic AF that don’t respond to routine Tx. Pulmonary vein isolation is part of Tx and aims to create a scar around pulmonary veins so that they are electrically isolated from atrium as ectopic pulmonary vein foci play significant role in AF initiation.
- delayed cardioversion
how would you assess risk of thromboemolism in an AF pt?
CHA2DS2-VASc criteria:
- congestive heart failure / LV dysfunction : 1p
- HTN: 1p
- age 75+ : 2p
- diabetes: 1p
- stroke/TIA/TE: 2p
- vascular disease (prior MI, plaque or aortic plaque): 1p
- age 65-74 yrs: 1p
- sex category female: 1p
Increasing score increases rate of stroke/TE. E.g. 8p = 11.1%/yr
how would you assess risk of bleeding in an AF pt?
HAS-BLED criteria:
- HTN (systolic BP >160 mmHg): 1
- abnormal kidney function (e.g. chronic dialysis, renal transplant, serum creatinine >200 umol/L): 1
- abnormal liver function (e.g. chronic hepatitis, raised bilirubin/ALT): 1
- stroke: 1
- bleeding (prev. bleed or disposition): 1
- untable labile INR/high INR: 1
- elderly (>65yrs): 1
- drugs (e.g. antiplatelets, NSAIDs) or alcohol abuse: 1 or 2
