Table of Contents
Page created on May 23, 2019. Last updated on November 15, 2021 at 21:41
I recommend reading through topic 1 and 2 of internal medicine for a better introduction to these conditions.
Atrial fibrillation
Atrial fibrillation (AF, Afib) is the most common supraventricular tachyarrhythmia. It always occurs in both atria at the same time. In Afib the atria contract rapidly but ineffectively and uncoordinatedly. There is no haemodynamically effective contraction and there is turbulence, which predisposes to thrombus formation.
Etiology:
- Pressure or volume load of the atria
- Hypertension
- Left-sided heart failure
- Pulmonary embolism
- Atrial ischaemia
- Coronary heart disease
- Hyperthyroidism
- Age-related fibrosis
Pathomechanism:
Something, often a re-entry circuit in the atria, takes over pacemaker function and produces chaotic and irregular impulses.
The atria contract ineffectively and therefore can’t fill the ventricles like normally. This is usually not a problem as the atrial contraction only accounts for 15% of ventricular filling anyway, so the ventricles are filled more than enough even without functional atria.
Not all impulses from the atria are conducted to the ventricles, as the AV node blocks most of them. Many of them are though, which usually causes irregular ventricular tachycardia.
ECG morphology:
- Absolute arrhythmia (R-R interval varies)
- Absence of P-waves
- Irregular ventricular rhythm
- f-waves may be present
- Look like fine shaking of the baseline
The presence of f-waves is not necessary for the diagnosis of Afib.
Clinical features:
Many cases are asymptomatic. If symptoms do occur, they’re often related to ventricular tachycardia, like palpitations and irregular pulse.
If an accessory conducting fibre is present (as in WPW), the impulses from the atria can bypass the AV node and cause life-threatening ventricular tachycardias.
Complications:
The turbulent blood flow inside the atria predisposes to thrombus formation. This thrombus can embolise and cause stroke.
The irregular ventricular rhythm may be haemodynamically unstable, causing symptoms of reduced cardiac output like syncope.
Treatment:
If the Afib is haemodynamically stable the patient should be treated with anticoagulants, often heparin. Rhythm control therapy like beta blockers can be used to control the rhythm.
If the Afib is not haemodynamically stable the patient should undergo cardioversion.
Atrial flutter
Atrial flutter is a less frequent supraventricular tachyarrhythmia. The etiology, clinical features and treatment is the same as for atrial fibrillation. The main difference between the two is that in atrial flutter the atria contract somewhat co-ordinately, which produces haemodynamically significant contractions.
The haemodynamically significant contractions actually make atrial flutter worse than atrial fibrillation, as they can cause blood to flow backwards.
Atrial flutter often converts into atrial fibrillation eventually.
ECG morphology:
- Absence of P-waves
- F-waves may be present
- Look like the teeth of a saw
- Atrial frequency 200 – 400/min
- Regular ventricular rhythm
The number of F-waves that are conducted to the ventricles (followed by a QRS) is important. Here are some examples:
- For every 2 F-waves 1 is conducted to the ventricles – block ratio of 2:1
- For every 3 F-waves 1 is conducted to the ventricles – block ratio of 3:1
- For every 4 F-waves 1 is conducted to the ventricles – block ratio of 4:1
- For every X F-waves Y is conducted to the ventricles – block ratio of X:Y
Ventricular fibrillation
Ventricular fibrillation (VF, V-fib) is a life-threatening arrhythmia characterised by disorganized, high-frequency ventricular contractions. These contractions are not haemodynamically significant and therefore cause a large drop in cardiac output, which becomes practically 0. Without defibrillation and resuscitation, sudden cardiac death occurs.
Etiology:
- Ischaemic heart disease
- Acute myocardial infarction
- Electrolyte abnormality
- Hypokalaemia
- Hyperkalaemia
ECG morphology:
- Arrhythmic, fibrillating baseline (> 300/min)
- Abnormal QRS complexes
- No P-waves
Treatment:
Immediate defibrillation and resuscitation are vital for survival. The underlying cause should be treated. Patients with recurrent untreatable V-fib can have an implantable cardioverter-defibrillator implanted.
Ventricular flutter
Ventricular flutter is similar to ventricular fibrillation as atrial flutter was to atrial fibrillation. Like V-fib it’s a life-threatening condition that needs immediate treatment. It often progresses into ventricular fibrillation. The causes and treatment are similar as for ventricular fibrillation.
ECG morphology:
- Sinusoid ECG curve (200 – 300/min)