Atrial fibrillation is a heart (cardiac) disease and the commonest sustained cardiac arrhythmia.
This article contains
Mechanism of Atrial fibrillation,
Causes of Atrial fibrillation,
Symptoms of Atrial fibrillation,
Diagnosis of Atrial fibrillation,
Types of Atrial fibrillation,
Treatment of Atrial fibrillation,
Rate control drugs,
Chemical Cardioversion/ Rhythm control drugs,
[Normal heart beats in a normal (sinus) rhythm. In cardiac arrhythmia this normal rhythm of heart beat is lost. Normal electrical system of heart Read more
Mechanism of atrial fibrillation
In normal sinus rhythm, the electrical Impulse of the heart starts at the SA node ( Sino-Atrial node) situated in the right Atrium. But in some conditions such as atrial fibrillation certain heart tissues other than SA node becomes capable of initiating electrical impulse of heart. These impulses originate from different sites are chaotic, irregular, rapid (atria may beat at a rate of 400 or more) and uncoordinated therefore causing weak, rapid and irregular atrial contractions.
As the force of contraction is weak, blood cannot be expelled properly to ventricles from atria and there is stagnation of blood in atria. These impulses reaches AV node, but the AV node cannot conduct all these impulses to ventricles and the ventricles usually beats at the rate of 120- 180 beats/minute and beats are irregularly irregular, although in Some cases, it may beat at a rate of < 100 beats/ minute ( slow atrial fibrillation) or even more than 200 beats/ minute.
Mechanism how atrial fibrillation originates and sustained is not well understood. Pulmonary veins, four in number, two superior and two inferior situated in the left atrium play an important role in atrial fibrillation. Left atrial musculature extends from the left Atrium to envelope the proximal part of the pulmonary veins. Enhanced automaticity and triggered firing from these muscles initiate atrial fibrillation. Reentry at Pulmonary vein and Pulmonary vein-left atrial Junction is potentially an important driver of atrial fibrillation.
The incidence of atrial fibrillation increases with age and occurs in 5 – 10 % of the population above 70 years.
It is rare in children in absence of structural heart disease or other pre-existing arrhythmia that may lead to atrial fibrillation.
Causes of atrial fibrillation
1 Coronary artery disease including myocardial infarction
2 Valvular heart disease mainly mitral stenosis
4 May Be triggered by other S.V.T ( supraventricular tachycardia) ( such as AVNRT )
5 Sick sinus syndrome
6 Congenital heart disease such as persistent atrial septal defect
8 Pericardial disease, myocarditis
9 Congestive heart disease
10 Lung diseases such as pneumonia, emphysema, COPD ( chronic obstructive pulmonary disease)
11 Pulmonary embolism
12 Viral infection
13 Hyperthyroidism and Hypothyroidism- sometimes atrial fibrillation may be the only sign of hyperthyroidism.
14 Exposure to stimulus – alcohol particularly in excess amount (binge drinking), caffeine, amphetamine, cocaine.
15 During acute or early recovery from major vascular, abdominal and thoracic surgery
16 Sleep apnea
19 Electrolyte imbalance
20 Idiopathic (where cause is unknown)- lone atrial fibrillation ( causes 30-40 % Of Paroxysmal atrial fibrillation and 20-30% of persistent atrial fibrillation).
Symptoms of atrial fibrillation
1 Some patients with atrial fibrillation are asymptomatic. In these patients atrial fibrillation is diagnosed when they are examined by a doctor clinically or some investigations such as ECG (Electrocardiogram) done for some other reason.
2 Palpitation- onset of atrial fibrillation may be felt as palpitation, sensation of irregular heartbeat.
3 Heart failure
5 Light headedness
8 Chest pain
9 Shortness of breath
11 Exercise intolerance
12 Due to ineffective left atrial contraction, left atrial dilatation, stasis of blood may lead to clot formation and there is risk of systemic thromboembolism (a blood clot obstruct a blood vessel after it dislodged from it’s site of origin) and its consequences.
How to diagnose Atrial fibrillation
1 Clinically there is irregularly irregular pulse. This irregularity cannot be resolved by exercise.
2 ECG (Electrocardiogram) – There are no P waves, because cardiac impulses originate from sites other than SA node. Baseline of ECG may show irregular fibrillary waves, Irregularly irregular QRS complexes with a rate usually 120-180 beats/minute.
3 Holter monitor and Event recorder- When atrial fibrillation is paroxysmal (it does not persist all the time) then one single ECG may not be able to diagnose atrial fibrillation because the patient’s heart rhythm may be normal during recording the ECG. In that situation the help of Holter monitor and Event recorder may be taken.
A holter monitor is a portable ECG machine that is kept with the patient by a belt or shoulder strap and it records heart activity for 24 hours or longer, as the time period is set. So this device records ECG for 24 hours or longer time and if there is atrial fibrillation within this time period it can diagnose atrial fibrillation.
Event recorder is also a portable ECG device which can record heart activity for weeks or months and it has one button which can be pushed by the patient when he/she feels some abnormality in heart activity such as rapid rate or irregularity of heart rate. Event recorder records ECG a few minutes preceding and following the pressing of button. Thus it can diagnose whether this abnormal feeling is due to atrial fibrillation or not.
After diagnosis of atrial fibrillation the following tests may be done
1 Echocardiogram- It uses ultrasound by a transducer to diagnose if there is any structural heart disease causing atrial fibrillation or if there is any blood clot in the heart as a consequence of atrial fibrillation.
2 Blood tests to see whether there is any abnormality in thyroid function, or electrolyte imbalance.
3 Chest xray to evaluate heart and lung conditions.
Types of atrial fibrillation
Atrial fibrillation can be categorized by the
(A) presence or absence of problem within heart valves ( Valvular and non valvular atrial fibrillation )
(B) duration of atrial fibrillation [ Paroxysmal, Persistent, Long-standing persistent and Permanent (Chronic) atrial fibrillation.]
Valvular atrial fibrillation– When the cause of atrial fibrillation is a heart valve whether it is artificial or a natural valve with a disease such as stenosis (stiffening) or there is regurgitation (reverse flow) of blood due to improper closing of that valve it is called valvular atrial fibrillation.
Non-valvular atrial fibrillation– When the cause of atrial fibrillation is not associated with a heart valve and it is caused by certain other reasons, sometimes the cause may be unknown.
Paroxysmal atrial fibrillation– When the episode of atrial fibrillation lasts less than one week it is called Paroxysmal atrial fibrillation. It is episodic and sometimes may be triggered by certain incidences such as heavy drinking, under extreme stress etc.
It may last from a few minutes to a few days. There may or may not be any symptom and the arrhythmia may resolve without any treatment.
Persistent atrial fibrillation– When atrial fibrillation persists at least one week it is called Persistent atrial fibrillation.
Long-standing persistent atrial fibrillation– when atrial fibrillation continues more than one year without any interruption it is called Long-standing persistent atrial fibrillation. Medications usually fail to resolve the condition and invasive treatment like electrical cardioversion/ catheter ablation/ pacemaker implantation is necessary in addition to medical management.
Permanent(Chronic) atrial fibrillation– When all modalities of treatment fail to resolve an atrial fibrillation it is called Permanent atrial fibrillation. In this situation drugs to lower heart rate and to prevent blood clot formation are used. Heart remains in a state of atrial fibrillation all the time.
Treatment of atrial fibrillation
Treatment of atrial fibrillation should be individualized according to the clinical situation of the patient. One or more treatment modalities may be required in a particular case.
Treatment options available-
1 Rate control drugs
2 Rhythm control drugs ( chemical cardioversion)
3 Electrical cardioversion
4 Catheter ablation- a) Radiofrequency ablation b) Cryoablation
5 Surgical ablation- a) Cox-Maze operation b) Mini-Maze operation c) Hybrid ablation.
6 Treatment of underlying disease that may cause atrial fibrillation such as hyperthyroidism, hypertension etc
7 Anticoagulant drugs to prevent thromboembolism
8 Lifestyle modification
Before treating a patient with atrial fibrillation the following factors must be considered
1 Hemodynamic status of the patient
2 Type of atrial fibrillation
3 Whether there is risk of stroke [by CHA2DVA2SC score (CHA2DS2 VASC is a scoring system to evaluate risk of ischemic stroke in a patient with atrial fibrillation)]
4 Whether the patient is already on anticoagulant and level of anticoagulation
5 Presence or absence of CAD (Coronary artery disease)
6 Presence or absence of structural heart disease
7 Presence or absence of hypertension
8 Any underlying cause of atrial fibrillation such as hyperthyroidism
If atrial fibrillation is due to some underlying cause such as hyperthyroidism that is to be treated.
There may be serious comorbid conditions such as sepsis, COPD, CHF ( congestive heart failure) which may give rise to rapid ventricular rate ( compensatory) and atrial fibrillation is incidental. In these cases use of rate and rhythm control drugs even electrical cardioversion may have serious adverse effects. So at first these underlying causes to be corrected.
If the patient is hemodynamically unstable, urgent electrical cardioversion may be necessary.
Rate control drugs-
Rate control drugs are used to slow the rate of atrial fibrillation –
1 Beta blockers– such as metoprolol
2 Calcium channel blocker– such as verapamil, diltiazem
Rate control is necessary i) to relieve symptoms in a symptomatic patient ii) to prevent tachycardia induced cardiomyopathy.
Digoxin is not commonly used alone in case of acute atrial fibrillation.
Rhythm control drugs ( antiarrhythmics) /Chemical cardioversion-
Use of antiarrhythmic drugs to restore sinus rhythm in atrial fibrillation is also known as chemical cardioversion. Two things to remember before attempting any cardioversion- (A) Slow the heart rate to <120/minute before cardioversion using rate control drugs to avoid risk of increased ventricular rate. (B) It is a good practice to perform a TEE ( transesophageal echocardiography) to see if there is a thrombus (blood clot) in the left atrium, especially if the duration of atrial fibrillation is >24 hours.
If there is a thrombus in the left atrium, cardioversion may be deferred. Not observing a thrombus in TEE does not exclude the risk of embolism.
If the atrial fibrillation is >12 hours of duration but there is high risk of thromboembolism (CHA2DS2 VASC score is ≥2 in men and ≥ 3 in women) anticoagulant treatment may be continued for at least 4 weeks (INR 2- 3) before cardioversion. (CHA2DS2 VASC is a scoring system to evaluate risk of ischemic stroke in a patient with atrial fibrillation)
If the atrial fibrillation is < 48hours duration and if there is no thrombus in the left atrium in TEE start heparin or LMWH ( low molecular weight heparin) simultaneously with cardioversion followed by administration of warfarin. Continue heparin/ LMWH until the INR 1.8 with the administration of warfarin. Then continue oral anticoagulant for at least 30 days after cardioversion. Thereafter anticoagulants may be continued according to CHA2DS2 VASC score.
If duration of atrial fibrillation is > 48 hours, rate control drug + anticoagulant may be used. After a period of minimum four weeks on anticoagulation and when INR ( International normalized ratio) is greater than 2 in two separate occasions, rhythm control drugs may be given.
Antiarrhythmic drugs such as Ibutilide (Class-lll), amiodarone(III), flecainide(Ic), propafenone(Ic), procainamide(Ia), Quinidine (la) are used to terminate atrial fibrillation.
In this procedure a device called a defibrillator is used to give electric shock to the heart with some abnormal rhythm to restore normal (sinus) rhythm.
Electrical cardioversion is usually used to treat atrial fibrillation. If rhythm control drugs fail to work or cause side effects or they stop working then Electrical cardioversion may be necessary. It is also used to treat atrial flutter, supraventricular tachycardia (SVT), ventricular tachycardia with pulse.
Electrical cardioversion is life saving in emergency situations. If the patient is hemodynamically unstable, urgent electrical cardioversion may be necessary. Read more
Catheter ablation is a minimally invasive procedure usually done by interventional cardiologists by which some abnormal heart rhythm is corrected. In this procedure the area from which abnormal heart rhythm originates or the area where arrhythmia sustains are destroyed by using radio frequency ( heat ablation) or cryofreezing ( using cold), or the the path through which abnormal rhythm enters the heart is blocked by destroying the path. Destroying this tissue helps restore the heart’s normal rhythm. Read more
Types of surgical ablation
i) Cox-Maze operation
ii) Mini-Maze operation
iii) Hybrid Ablation.
Cox-Maze operation– Original Cox-Maze operation performed by Dr James L. Cox in 1987. It is an open heart surgery and usually done at the time when the heart needs surgery for another reason also, such as for coronary artery bypass surgery or heart valve surgery. A standard sternotomy done. Heart lung bypass machine is used. Incisions are made in both atria in such areas which are responsible for initiation and propagation of atrial fibrillation, thus allowing heart to beat with its normal sinus rhythm.
Mini-Maze operation– Since the introduction of Cox-Maze operation modifications have been made such as Cox-Maze ll and Cox-Maze lll. The latest version is Cox-Maze lV introduced in 2002. In this procedure small incisions in chest wall done. A fiber optic camera is introduced through the incision to visualize the heart. Several lesions are made in atria by using bipolar radio frequency or cryotherapy instead of cutting atria.
It is a minimally invasive procedure with fewer complications than the original Cox-Maze operation. Sometimes left atrial appendage is also removed during the procedure to prevent stroke and to reduce anticoagulant requirement. Full effect of surgical ablation may take place after several months so during this period antiarrhythmic medications and anticoagulants should be taken.
Hybrid ablation– Hybrid ablation means applying both Mini-Maze procedure along with catheter ablation.
Complications of surgical ablation– Bleeding, Infection, arrhythmia, stroke.
Success rate of Cox-Maze operation is 80- 95% and it significantly lowers the need for anticoagulation therapy.
To eat heart healthy food
Moderate physical activity and aerobic exercise
Limit alcohol intake
Stop taking substances which precipitate atrial fibrillation