DEFINITION OF ATRIAL FIBRILLATION
ATRIAL FIBRILLATION ….It is essentially an atrial disturbance due to multiple ectopic foci causing an absolutely irregular ventricular response affecting the pulse in its rate, rhythm and volume so that no two beats are equal. That is why this condition is also called “delirium cordis”, i.e. heart in a state of delirium. It is the commonest chronic arrhythmia.ATRIAL FIBRILLATION
- Focal irritation with discharge.
- Re-entry or reciprocal mechanism.
Circus movement and Prinzmetal’s theory were put forwarded to explain this cardiac arrhythmia. The atrial pulsation varies from 400 to 600 per minute but the ventricles only respond to about 80 to 180 beats per minute; while the pulse beat varies from 100 to 120 per minute, therefore a Pulse deficit always exists (usually more than 20 beats per minute). ATRIAL FIBRILLATION
- Rheumatic heart disease, commonly mitral stenosis, other non-rheumatic valvular heart disease.
- Endocrinopathies particularly thyrotoxicosis, others include hypothyroidism, phaeochromocytoma.
- Ischaemic heart disease with or without myocardial infarction e.g. coronary sclerosis or coronary thrombosis.
- Hypertensive heart disease.
- Other cardiac conditions like cardiac surgery, particularly atriotomy, pulmonary embolism, endocarditis, dilated cardiomyopathy, ASD, mitral valve prolapse, etc.
- Drugs, e.g. Emetine, Aconite, Digitalis in toxic doses; alcohol excess or alcohol withdrawal or even small amount of alcohol consumption (Holiday heart), Theophylline, B- adrenergic agonist.
- Acute febrile diseases with associated carditis, e.g. diphtheria, acute rheumatic fever, pneumonia etc.
- Septic foci e.g. acute appendicitis, subdiaphragmatic abscess, etc. But these are very rare.
- Disease or conditions where pericardiumn is involved, e.g. constrictive pericarditis, bronchogenic carcinoma involving the pericardium or operations on the pericardium.
- Lone atrial fibrillation: It occurs in absence of any demonstrable heart disease or hypertension in subjects of less than 65 years associated with low risk of stroke.
- Atrial fibrillation may also be seen in cases of atrial flutter after digitalis therapy.
Atrial fibrillation is uncommon in congenital heart disease, pulmonary heart disease and in aortic valve diseases.
- Chest trauma. It affects 10% of subjects above the age of 80 years.
- Effort dyspnoea.
- Angina, syncope, fatigue.
- Symptoms of original disease.
- There may be no symptom.
Atrial fibrillation is rarely a life threatening disease but at times may be problematic when the ventricular rate is very high to precipitate hypotension, myocardial ischamia or tachycardia induced myocardial dysfunction.
Atrial fibrillations may be paroxysmal and refractory.
Pulse is absolutely irregular, average rate is 100 to 120 per min, volume varies from beat to beat but on an average is Neck veins are usually engorged, pulsations are scanty, BP is low. Oedema may be present.
Examination of Heart
There is gross cardiac irregularity which increases after slight exercise. Average heart rate varies from 80 to 180 beats per minutes.
Thus pulse deficit is usually present. In case of mitral stenosis the presystolic accentuation of mitral murmer may disappear (though murmur remains) because this is due to active atrial contraction which is, however, absent in this condition.
Abdominal examination may reveal enlarged and tender liver due to congestive cardiac failure which very often follows this condition.
Most serious consequence is the tendency for thrombus formation in the atria particularly in the appendages and Embolic manifestation particularly cerebral embolism.
Individuals with marked obstructive valvular diseases, chronic heart failure, hypertension, dialysis, left ventricular dysfunction, aged individual (more than 75 years) or with a history of previous embolic episodes are at special risk of embolization.
ECG shows characteristic ‘f’ or fibrillary waves and absence of P waves.
- Atrial flutter with varying degree of block
- Sinus arrhythmia with tachycardia.
- Multifocal (chaotic) atrial ectopics.
Treatment should be aimed at relief of symptoms, control of ventricular rates and prevention of thromboembolic episodes.
Paroxysmal and recent onset Atrial fibrillation Drugs
In case of haemodynamic instability or in presence of precipitating factors, urgent cardioversion is usually needed. Initial shock with 100-200 joules is administered in synchrony with ‘R’ wave of ECG. If sinus rhythm is not restored, shock with 360 joules may also be given.
When atrial fibrillation exists for several days then cardioversion is followed by anticoagulation with warfarin. However it should be remembered that for newly diagnosed lone atrial fibrillation’ with slow rate no treatment or hospitalization is required.
For in patients treatment IV Verapamil is the drug of choice, 2.5 to 5 mg every 1-2 minutes upto 20 mg can be given. This is followed by oral therapy. Inj. Diltiazem 2.5 mg/ kg IV for 2 minutes followed by 0.35 mg/kg if necessary. This is best suited for cases with IV dysfunction.
Inj. Esmolol 500 ug/kg IV for 1 minute followed by 25- 200 ug/minute may also be given.
Inj. Digoxin 0.5-0.75 mg can be started followed by 0.25 mg every 6 hours till a total dose of 1-1.5 mg is reached.
In atrial fibrillation with WPW syndrome the above agents are not used. Cardioversion with Direct Current shock (DC shock) may be given.
Anticoagulation with warfarin is required as long as atrial fibrillation exists. But is not required in patients who are under 60 years of age and where no additional risk for stroke exists.
Refractory Atrial Fibrillation
Two or 3 drug combination of B-blocker or calcium channel blocker and digoxin may be useful for controlling rates. At times Amiodarone may be added in addition.
If all drugs fail radio frequency AV-node ablation and permanent pacing may be required. Multiple re-entry circuits may be stopped by surgery (Maze procedure).
Implantable atrial defibrillators can also be used.
Chronic Atrial fibrillation
The patient should be digitalised which will slow the ventricular rate and will improve myocardial efficiency. It should be stopped 48 hours before cardioversion.
Quinidine may also be used along with digitalis but unsuitable for mitral stenosis cases.
Propranolol may also be used if no heart failure exists and if Digoxin fails to restore the normal rhythm.
Calcium entry blocker Verapamil may be used when Propranolol is contraindicated. Usual dose is 5-10 mg I. V. It should not be added with Propranolol.
Cardio version with Direct Current shock (DC shock)
Immediate cardioversion is required when there is angina, heart failure or hypotension. Even if the heart rate is controlled a decision must be taken whether cardioversion should be attempted for establishment of sinus rhythm. Conversion is recommended when
- Atrial fibrillation is of recent onset (<12 months)..
- Left atrium not hugely dilated (<45 to 50 mm Echocardiogram)
- There is absence of atrial clot.
As there is a risk of embolism after cardioversion if it is not emergency then prior anticoagulation with warfarin should be done for 3-4 weeks. Before cardioversion, Quinidine 300 mg every 6 hours for 24 hours should be given to prevent recurrence. Pharmacologic cardioversion can also be done with Quinidine 200-300 mg every 6 hours. Unless precipitating cause is removed, fibrillation often recurs in 50% to 70% of cases. Use of Quinidine or other class 1la agents will be helpful to maintain sinus rhythm.