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| Atrial fibrillation |
Atrial Fibrillation
Definition:This is an arrhythmia where atria are disorganised and multiple atrial foci fire impulses at a rate of 350-600 per minute. There is no atrial contraction but only fibrillation. The ventricles respond at irregular intervals, usually at a rate of 100-140/min.
It can be paroxysmal or persistent.
Aetiology:
1. Rheumatic heart disease.
2. Ischaemic heart disease.
3. Hypertension.
4. Thyrotoxicosis.
5. Congenital heart diseases.
6. Cardiomyopathy.
7. Pericardial diseases.
8. Lone atrial fibrillation occurs in elderly patients without underlying heart disease.
Pathophysiology and haemodynamics.
1. Atria fire the impulse at a rate of 350-600/min. Many of them reach the AV node in the refractory period, and so not conducted. However, a variable number of impulses are conducted to the ventricles at irregular intervals. This accounts for the irregularly irregular rhythm of pulse and heart.
2. The irregular rhythm of heart results in varying durations of diastole, the lesser the ventric volume and the longer the diastole, the higher the ventricular volume. The ventricular volume in turn determines the cardiac output, which hence keeps varying. This varying cardia output accounts for the warying volume of pulse deficit.
3. Lack of atrial contraction results in the following.
a. Stasis of Blood in the left burgun resulting in thronat formation and subsequent dislodgement of the thronat resulting in sustemic embolisation:)
b. Disappearance of a wave from JVP.
c. Disappearance of fourth heart sound he it was present.
d. Disappearance of the pre-systolic accentuation of the mid-diastolic murmer of mitral stenosis in some cases.
4. Tachycardia-related cardiomyopathy in patients with poor rate control may further depress cardiac function.
Risk of stroke in atrial fibrillation.
CHADS2 index. It has following components. The numerals in front of the components indicate the score.
Congestive heart failure 1
hypertension 1
age more than 75 years 1
diabetes mellitus 1
stroke history 2
score of 6 predicts a stroke of 18.2 per 100 patient-years.
Symptoms
1.palpations
2.fatigue
3. Syncope
4. Angina
5. Symptoms of cardia failure and thromboembolism.
Signs.
Irregularly irregular pulse.
Varying volumes of pulse.
Pulse deficit.
Varying intensity of first heart sound.
Absence of a water onJVP
disappearance of the PSA of the MDA of MS in some cases.
Disappearance of the fourth heart sound.
Hypottension
electrocardiogram
. An irregularly irregular rhythm of QRS complexes.
. Absent P wave.
. Small, irregular wave at a rate of 350-600/min .
Differential diagnosis.
. Atrial flutter with variable block. Prominent saw-tooth waves at lower rates of 250-350/min are seen in the ECG.
. Atrial tachycardia with vagable block. Atrial rate 150/min approximately which is regular but the and to the wentsic is not regular producing irregular pulse.
. Multifocal burial tachycardia.
Complications.
.Syncope
. Thromboembolism
. Precipitation of cardiac failure.
.Angina
. Hypottension.
. Precipitation of pulmonary offenc in nitrat stenosis.
Treatment.
Goals of management.
. Haemodynamic stabilization.
.Control of ventricular rate.
. Restoration of shots rhythm.
. Prevention of emboli complications.
. Treatment of underlying cause.
1. If the patient 's clinical status is not severely compromised, synchronized DC cardioversion starting at 100J is the treatment of choice.
2. He the patients clinical status is not peter compromised, treatment is in two steps :
a. Slowing the ventricular rate with verapamil, diltiazem, propranolol, esmolol or digoxin. The doses of various drugs are.
Diltiazem:10mg intravenously over 2 min, repeat same ford in15 minutes if required ; start an infusion at 10-15 mg/hr to maintain ventricular rate below 100/minute.
Digoxin:0.25 -0.5 mg intravenously, then 0.25 mg after 4-6 hours joe another ford after another 12 hours.
b. Converting rhythm to normal shots rhythm.
Amiodarone 5-7 mg/kg iv over 1 hour followed by 1.2-1.8gm/24 hour infusion.
If medical cardioversion fails, electric cardioversion is performed after 3 weeks of warfarin therapy which is continued for another 4 weeks after cardioversion.
3.Quinidine or amiodarone may be used to prevent recurrence.
4. If cardioversion is unsuccessful or in which it is likely to reccur, allow the patient to remain in atrial fibrillation but reduce the ventricular rate by digitalis, verapamil or propranolol. Or give chronic anticoagulation
5. Antithromantic therapy is indicated in the following situations:
a. Duration of atrial fibrillation exceeds 48 hours
b. If atrial thrombi are seen on echocardiography. Warfarin is administered for 3 weeks prior to cardioversion. It is continued for another 4 weeks after cardioversion.
6. In paroxysmal atrial fibrillation., preservation of shots rhythm can be achieved quinidine, amiodarone.
7. Refractory cases managed with antitachycardia racemclers or inducing complete heart block by ablation of bundle of His followed by permanent pacemaker implantation.
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