Pathophysiology of atrial fibrillation (AF)

A healthy heart's electrical system

Controls the rate and rhythm of the heartbeat

With each heartbeat, an electrical signal spreads from the top of the heart to the bottom. As the signal travels, it causes the heart to contract and pump blood. The process repeats with each new heartbeat.

The Electrical Problem in Atrial Fibrillation

The heart's electrical signals don't begin in the SA node.

Commonly begin in the left atria or in the nearby pulmonary veins.

The signals don't travel normally and spread throughout the atria in a rapid, disorganized way causing the atria to fibrillate (quivering)

The firing of these impulses results in a very rapid and disorganized heartbeat.

The rate of impulses through the atria can range from 300 to 600 beats per minute

As the AV node limits the number of impulses it allows to travel to the ventricles, the pulse rate is often less than 150 beats per minute, but this is fast enough to cause symptoms.

So, even though the ventricles may be beating faster than normal, they aren't beating as fast as the atria.

Thus, the atria and ventricles no longer beat in a coordinated way.

This creates a fast and irregular heart rhythm. In AF, the ventricles may beat 100 to 175 times a minute.

As only a small amount of blood enters the ventricles, the normal force created by the cardiac muscles decreases and only a small amount of blood is ejected from the heart. (frank-starling law of the heart)

The body gets rapid, small amounts of blood and occasional larger amounts of blood.

Most of the symptoms of AF are related to how fast the heart is beating. If medicines or age slow the heart rate, the symptoms are minimized.

AF may be brief, with symptoms that come and go and end on their own. Or, the condition may be persistent and require treatment.

Sometimes AF is permanent, and medicines or other treatments can't restore a normal heart rhythm.

Tends to become a chronic disease as molecular and structural changes occur and makes it hard to achieve sinus rhythm

Video at http://www.nhlbi.nih.gov/health/dci/Diseases/af/af_what.html

References : http://www.ncbi.nlm.nih.gov/pmc/articles/PMC546076/ , http://www.webmd.com/heart-disease/atrial-fibrillation/heart-disease-atrial-fibrillation-basics , http://www.mayoclinic.com/health/atrial-fibrillation/DS00291 , http://www.medscape.com/infosite/atrial-fibrillation/article-2

Differential Diagnosis by Shakir and JB

Atrial Fibrillation

- Occuring in 5-10% of patients over 65 years

- Deterioration of exercise capacity

- Irregular pulse

- ECG shows fine oscillations of the baseline

- No clear P waves

- QRS rhythm is rapid and irregular

- Ventricular rate around 120-180 per minute

- Palpitations

- Decreased blood pressure

- Weakness

- Dizziness

- Confusion

- Shortness of breath

- Chest pain

Sick Sinus Syndrome

-Fatigue

-Dizziness

-Syncope

-Chest pains

-Insomnia

-Confusion

-Palpitations

Endocarditis

- Fever

- Chills

- Heart murmurs

- Fatigue

- Aching joints and muscles

- Night sweats

- Shortness of breath

- Paleness

- Persistent cough

- Swelling in lower limbs or abdomens

- Weight loss

- Haematuria

- Spleen tenderness

- Osler's nodes (red tender spots under skin of finger)

- Petechiae (tiny purple red spots on skin, sclera, or inside mouth)

Holiday Heart Syndrome

- Acute cardiac rhythm and/or conduction disturbance

- Supraventricular tachyarrythmia

- Associated with heavy ethanol consumption with no other clinical evidence of heart disease

- Resolve rapidly during subsequent abstinence from alcohol use

- ECG shows prolongation of the PR, QRS, and QT intervals compared with patient's who experienced arrhythmias in the abscence of alcohol consumption

- Palpitations

- Chest discomfort

- Shortness of breath

- Feeling of faintness

Wolff-Parkinson-White Syndrome

- Electrical Syndrome arrive at the ventrical too soon

- A category of electrical abnormality known as "pre-excitation syndromes"

- ECG will show that an extra pathway or shortcut exists from the atria to the ventricles

- May have dizziness, chest palpitations, fainting or rarely, cardiac arrest

Supraventricular Tachycardias (SVTs)

-Unlike atrial fibrillation, SVTs arise from atrium or atrioventricular joint

- Has P wave as SA node will be working

Paroxysmal Atrial Fibrillation

- Irregular in rhythm

- Start abruptly

- Terminate as suddenly

- Lead to symptoms such as syncope, presyncope, dyspnoea or chest pain

- May have episodes only a few times a year or every day

Atrial Flutter

- Shares clinical presentation with atrial fibrillation

- Organized atrial rhythm with an atrial rate between 250 & 350 beats per minute

- ECG shows regular sawtooth- like atrial flutter waves (F waves) between QRS complexes

- Ventricular rate of 150 b.p.m.

- Occasionally heart rate of 300 b.pm.

Reference : Clinical Medicine by Kumar & Clark, http://heart.emedtv.com, www.emedicine.medscape.com, www.mayoclinic.com

Treatment & Management of Atrial Fibrillation (Rate Control , Anticoagulants and Antiplatelets Medications)

· Rate Control Medications

· Control the heart rate particularly the ventricular beats

· The goal of the medication is to slow the heart rate between 60-100 beats a minute

a) Beta Blockers

· They slow down the conduction rate by:

I. Decreasing the rate of SA node

II. By slowing down conduction through AV node

III. By making the AV node less sensitive to A-Fib impulse

· Eg of beta blockers propranolol and metaprolol

b) Calcium Channel Blockers (CCB)

· CCB prevents or slow the flow of calcium ions into smooth muscle such as the heart

· Verapamil and diltiazem are eg of CCB

C) Digoxin

· Helps slow the heart rate by blocking the number of electrical impulses that pass through the AV node into ventricles

· Lanoxin and Digitek are eg of digoxin

· Anticoagulants Drugs

· Anticoagulants inhibit the ability of blood to clot or coagulate

· Warfarin and Heparin are some eg of anticoagulants

· Antiplatelet Drugs

· Prevent formation of clots

· Aspirin is the most common antiplatlet drugs

· Others include Plavix and Ticlid

Management (surgical)

Surgical interventions

The Maze procedure

It consists of creating incisions in the atrium that disrupt the re-entrant circuits which are then sewn together again. This results in the blood still being able to be pushed into the ventricle from the atrium but the electrical impulse cannot cross the incisions. Thus there is only one pathway that the electrical impulse can travel from SA node to the AV node. The atrium can no longer fibrillate, and sinus rhythm (the normal rhythm of the heart) is restored.

Indications
It is not required for most patients with atrial fibrillation as either
- they are not bothered by the rhythm
- the medications used are able to control it
- catheters can be used to disrupt the circuits

Surgery is only required if patients feel troubled by the atrial fibrillation or the convenience of not having to take medications. Patients with atrial fibrillation who suffered stroke before are advised to undergo surgery as their risk for another stroke is higher.

Risk
As it is an "open heart" procedure requiring cardiopulmonary bypass (the heart-lung machine) there are risks of fluid retention, pneumonia, stroke, kidney failure, other organ failure and death. Some patients also require a permanent pacemaker postoperatively. This is thought to be due to underlying disease of the SA node.

Results
It is highly effective in restoring sinus rhythm but it is around 80-100%

Cardioversion

Converting AF to a normal rhythm can be done in 2 ways: chemical and electrical cardioversion.

Patients who are more likely to get better:
• Patients younger than 65 years of age
• Patients who have had AF for a short time (less than 12 months)
• Patients with normal-sized atria and ventricles
• Patients who are having their first episode of AF

The medication work by blocking channels on blood vessels that allow ion travel. Amongst them are:
• flecainide
• beta-blockers
• amiodarone.

However, these come with a disadvantage:
They carry a small risk of causing other abnormal heart rhythms-- said to be pro-arrhythmic. Especially in patients with diseases of the heart muscle or coronary arteries, which are more life threatening than AF. Treatment with these medications often is initiated in the hospital while the patient's rhythm is continuously monitored for 24-72 hours.

The medication also brings about side effects. An example would be that amiodarone interacts with warfarin and increases the risk of bleeding. The most severe side effect of amiodarone is lung toxicity that potentially can be fatal.

Electrical cardioversion requires the administration of an electrical shock over the chest. This electrical shock stops the abnormal electrical activity of the heart for a brief moment and allows the normal heart rhythm to take over. Warfarin usually is given for 3 to 4 weeks prior to and after successful cardioversion.
95% success rate.

There is little utility in cardioverting stable patients with permanent atrial fibrillation, and the goal in this group is rate control.

Limitations:
Approximately 75% of patients successfully treated with electrical cardioversion experience a recurrence of AF within 12-24 months. Older patients with enlarged atria and ventricles who have had AF for a long time are especially prone to recurrences.

Internal cardioversion uses a device called an implantable cardioverter defibrillator (ICD). This device delivers an electric shock to your heart. An implantable cardiac defibrillator is placed in people who are at high risk of sudden cardiac death from dangerous arrhythmias such as ventricular tachycardia or ventricular fibrillation.

Complications & Prognosis of Atrial Fibrillation

Complications

Blood Clots

Basically, when the atria do not contract normally, in this case, a weak contraction, blood tends to pool in the atria instead of being pumped into the ventricles. Hence, quite obviously, pooled blood will form blood clots. Now, these blood clots can do just about anything other blood clots can. More complications can occur, such as...

Pulmonary Embolism & Stroke

Now, we can expect the blood clot to travel to a vessel in the lung, blocking it, thus causing a pulmonary embolism. The same blood clot can also actually travel to a vessel in the brain, causing a stroke. These are major complications, of course. The same blood clot can actually block blood flow in just about any vessel in the body.

Congestive Heart Failure

This complication arises when frequent periods of atrial fibrillation (said to last longer than a few months) have stretched out the walls of the heart, thus, weakening the heart. Now, your heart is too weak to push or pull blood from the body's vessels. Without enough power, blood gets congested, usually, but not limited to, the lower peripheries, thus causing swelling. The same can also happen in the lungs, making it harder to breathe, especially while lying down.

Link : http://heart.emedtv.com/atrial-fibrillation/atrial-fibrillation-complications.html

Prognosis

I'm leaving links to specific articles which may be useful to those who are interested in the specifics. But in a heartbeat, patients with atrial fibrillation can be classified into low, intermediate, and high risk patients. And the prognosis for each is different.

High-risk factors include prior stroke, transient ischaemic attack (mini stroke), and systemic thromboembolism.

Moderate-risk factors include age older than 75 years, hypertension, heart failure, and diabetes mellitus.

Risk factors of unknown significance include female gender, age 65-74 years, coronary artery disease, and thyrotoxicosis.

Basically, the prognosis become better, for people in the low-risk category.

Generally, in another research shown, patients with paroxysmal AF have the same mortality rate as patients without AF. However, with increased age, paroxysmal AF may evolve into chronic AF, which carries a higher mortality rate.

Also, note that prognosis is good for an AF patient, if cause of AF is found and treated.

Link: http://emedicine.medscape.com/article/151066-overview

http://www.biomedcentral.com/1471-2261/5/20#B18

Atrial Fibrillation Causes and Risk Factors

Mnemonic: ASI PIRATES



A lcohol(HH)
Increases Secretion of epinephrine and norepinephrine and increases sympathetic output.



S moking
Smoking causes fibrosis of atrial walls via nicotine. CS also promotes endothelial dysfunction and atherosclerosis is vascular bed.




I nfection (pneumonia and sepsis)




P ulmonary: PE, COPD



I atrogenic
Previous history of cardiac surgery and administration of drugs.



R heumatic heart disease: mitral regurgitation
Mitral =bicuspid. Backflow of blood from left ventricle to left atrium. Heart must work harder to pump blood to body.



A therosclerotic: MI, CAD




T hyroid: Thyrotoxicosis(Hypo and hyperthyroidism)
Hypo: When not enough thyroid hormone is present neither the heart nor the blood vessels function normally. heart muscle is weakened in both its contraction phase, and also its relaxation phase.




E ndocarditis
Inflammation of endocardium. Impulse transmission disrupted.








S ick sinus syndrome
A collection of heart rhythm disorders which include bradycardia, tachycardia or alternating.
Tachycardia that starts at the upper chamber=A-fib.

Investigations

ECG

Measurement

Heart rate

PR interval, Normal: 0.12 – 0.20 seconds

QRS duration, Normal: 0.06 – 0.10 seconds

QT interval

QRS axis in frontal plane

Rhythm Analysis

Look at the pattern of the waves and see the abnormalities or consistencies

Conduction Analysis

Basically, look at PP intervals

Waveform Description

P wave: the activation/depolarization of the right and left atria

QRS complex: right and left ventricular depolarization

ST-T wave: ventricular repolarization

U wave: origin for this wave is not clear - but probably represents "after depolarizations" in the ventricles

PR interval: time interval from onset of atrial depolarization (P wave) to onset of ventricular depolarization (QRS complex)

QRS duration: duration of ventricular muscle depolarization

QT interval: duration of ventricular depolarization and repolarization

RR interval: duration of ventricular cardiac cycle (an indicator of ventricular rate)

PP interval: duration of atrial cycle (an indicator of atrial rate)

Transthoracic Echocardiogram

A test which is used to reflect images of the heart using ultrasound technology by means of a transducer (probe).

The transducer emits high frequency sound waves ( inaudible by the ear) which are directed to the heart. As the sound waves encounters different structures, they will be reflected back to the probe, which then will be interpreted as images (2D). Images will be shown on the screen.

Done by sonographer, interpreted by cardiologist, takes about 30-60 minutes.

Uses

Assess the size of heart chambers

Look at cardiac muscle and valves function

Blood clots and masses in the heart

Presence of defects between the heart chambers

Abnormalities of blood flow in the heart

Pericardial diseases (accumulation of fluid)

Transoesophageal echocardiogram (TOE)

-A scope containing an ultrasound transducer, is passed into the patient’s oesophagus

-Evaluate for left atrial thrombus

-To guide cardioversion unless a thrombus is found

Advantage over TTE

-Better view those structures located deeper in the body

-Travel less to the heart to minimize the attenuation of ultrasound signal -> enhancing image and Doppler quality

-Aorta, pulmonary artery, valves of the heart, both atria, atrial septum, left atrial appendage, and coronary arteries have better views with TOE.

-TEE has a very high sensitivity for locating a blood clot inside the left atrium.

-To evaluate, diagnose, and treat patients in the peri-operative period. Most commonly used during open heart procedures

Disadvantages

-Requires fasting patient

-Requires a team of medical personnel

-Longer

-Uncomfortable

-Risks with oesophageal perforation or adverse reactions with medication or anesthetic

CT/MRI

Computed tomography (CT) or magnetic resonance imaging (MRI): If atrial fibrillation ablation is planned, then 3-dimensional imaging technologies (CT scan or MRI) are often helpful to evaluate atrial anatomy. Imaging data can be processed to create anatomic maps of the left atrium and pulmonary veins.

Blood tests

Complete blood count, thyroid, hepatic, and renal function panels are often helpful, especially when ventricular rate is difficult to control. Help to rule out thyroid problems or other substances in the blood that may lead to atrial fibrillation.

Holter monitor

A portable machine that records all heartbeats. Records information about the electrical activity of the heart as a person goes about their normal activities for a day or two. A button can be pressed when symptoms are felt so that the doctor can know the heart rhythm present at that moment

Chest X-ray

Help the doctor to see the condition of the lungs and heart. Can be used to diagnose other conditions and rule out atrial fibrillation

Electrophysiology study

Help see if there is a problem with heartbeat