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Atrial Fibrillation

Atrial Fibrillation (AF or A-fib)

Atria and Atrial Fibrillation

• AF most commonly occurs in:
• Structurally altered atria (ischemia of the atria)
• Electrically altered atria (changes in action potential)
• Most common causes of atrial remodeling:
• Ischemic heart disease
• Arterial hypertension
• Valve defects
• Mineral imbalances
• Hypokalemia
• Hypomagnesemia
• Thyrotoxicosis
• Pulmonary embolism
• Pericarditis
• Cardiomyopathy
• Various medications (especially antiarrhythmics)
• Remodeled atria
• Create a substrate (environment) for the onset and maintenance
• Abnormal electrical activity (action potential)
• Any supraventricular arrhythmia can develop
  
  
• Idiopathic atrial fibrillation
• occurs in unchanged atria from an unknown cause (it is rare)

• In the atria, there are numerous micro re-entries
• They independently generate impulses with a frequency of 350-600/min.
• In each re-entry, the impulse circulates around
• There are at least 10 micro re-entry circuits
• Micro re-entry circuits
• Are most often triggered by atrial ectopy
• Require a substrate (remodeled atria) to be maintained
• If there are 3 micro re-entries, multifocal atrial tachycardia will develop
• A single macro re-entry creates atrial flutter

Maternal Re-entry and Activation Waves

• The mechanism is the same as above, but in the atria there is a maternal re-entry
• From the maternal re-entry, numerous activation waves emerge, each activating the atria
• The activation waves can again create micro re-entries
• The atria have a frequency of 350-600/min.
• One micro re-entry creates intra-atrial re-entry tachycardia

ECG and Atrial Fibrillation

• Rhythm (RR interval) is irregularly irregular
• Deformed isoelectric line
• P waves are not present
• Atria with a rate of 350-600/min create what is known as fibrillatory waves (f waves)
• Atrial fibrillation (AF) is sometimes classified based on the amplitude of fibrillatory waves (similar to ventricular fibrillation) into:
• Fine AF - amplitude < 0.5mm
• Coarse AF - amplitude > 0.5mm
• QRS complexes are narrow (<0.12s) (because impulses pass to the ventricles through the AV node)
• QRS complexes can be widened by: (aberrant conduction)
• WPW syndrome (if the ventricles are activated through an accessory pathway)
• Pre-existing Tawar's block (right bundle branch block, left bundle branch block)
• Functional Tawar's block occurs in tachycardia due to (Ashman's phenomenon)

Atrial Fibrillation

• Heart rate is irregularly irregular (RR intervals vary)
• QRS complexes are narrow (<0.12s) because the ventricles are activated through the AV node and an intact conduction system
• Deformed isoelectric line - P waves cannot be differentiated
• This is Coarse atrial fibrillation because the amplitude of the isoelectric line is > 0.5mm

Ashman Phenomenon

• With prolonged RR intervals, the refractory period of the conduction system is also prolonged
• Ashman phenomenon is an aberrant conduction that occurs when a prolonged RR interval is followed by a shortened RR interval
• Shortened RR intervals have a prolonged refractory period
• Which has not yet shortened from the previous prolonged RR interval
  
  
• It is true that the Right Tawar Bundle (RTB) has a longer refractory period compared to the Left Tawar Bundle (LTB)
• If an impulse passes through the AV node to the ventricles at a time
• When the Right Tawar Bundle is in the refractory period
• It results in a functional blockade of the Right Tawar Bundle
• The mentioned functional blockade most commonly occurs during atrial fibrillation
• When after a long RR interval a short RR interval with a QRS complex (which has the shape of RTB) follows

Concealed Conduction

• Laddergram illustrates the propagation of impulses through the conduction system
• A - atria, AV - AV node, V - ventricles
• In atrial fibrillation (AF), the AV node is irregularly bombarded by impulses from the atria at f: 350-600/min.
• When impulses partially penetrate the AV node, they alter its electrical properties
• The AV node then changes the conduction speed of the subsequent impulse (concealed conduction)
• This results in an absolutely irregularly irregular ventricular (QRS) response

Differential Diagnosis of Atrial Fibrillation

• Atrial fibrillation is a supraventricular arrhythmia
• On an ECG, it often resembles:
• Atrial flutter (with variable conduction to the ventricles)
• Multifocal atrial tachycardia
• Differential diagnosis of supraventricular arrhythmias

Atrial Flutter with Variable Conduction (2:1 and 4:1)

• Atrial Flutter
• There is one macro re-entry circuit around the entire right atrium
• The impulse circles in the macro re-entry with a frequency of 300/min
• Instead of P waves, the ECG shows Flutter (F) waves (sawtooth pattern) with a frequency of 300/min
• The heart rhythm is regularly irregular
• One RR interval has a 2:1 conduction ratio to the ventricles
• The next RR interval has a 4:1 conduction ratio to the ventricles

Classification of Atrial Fibrillation

• Atrial fibrillation is classified according to its duration
• In addition to a standard ECG, the following are used for classification:
• 24-hour ECG Holter (a 24-hour, sometimes 48-hour ECG recording)
• Implantable ECG recorder (provides approximately 30-day ECG recording)
• 30-second rule
• Atrial fibrillation (AF) must last at least 30 seconds
• If AF lasts less than 30 seconds, the patient does not have the diagnosis of atrial fibrillation
• Although it is fundamentally atrial fibrillation
• This is a consensus, as episodes of AF shorter than 30 seconds are said not to form thrombi?
• Paroxysmal Atrial Fibrillation
• An episode of AF lasts at least 30 seconds and less than 7 days
• Spontaneously terminates (without treatment)
• Paroxysms may recur, and the patient may experience:
• The 3rd episode of AF
• The 4th episode of AF, etc.
• If AF lasts more than 48 hours, atrial remodeling occurs
• And spontaneous termination of AF is unlikely
• AF often starts as recurrent paroxysms and gradually (without treatment) progresses to:
• Persistent AF
• Permanent AF
• Persistent Atrial Fibrillation
• An episode of AF lasts more than 7 days
• Does not spontaneously terminate
• After 7 days, the atria are remodeled and create a substrate for maintaining AF
• The chance of spontaneous conversion to sinus rhythm is almost zero
• Termination of the episode requires medication or electrical cardioversion (electrical shock)
• Long-standing Persistent Atrial Fibrillation
• An episode lasts more than one year
• But there is still a chance for termination, such as through electrical ablation
• Electrophysiological examination detects micro-reentry circuits and they are "burned out" (ablation)
• Permanent Atrial Fibrillation
• AF lasts more than one year
• It is accepted by both the doctor and the patient, and there is no plan for conversion to sinus rhythm
• Medication is used to control ventricular response (frequency of QRS complexes)
• In remodeled atria, the chance of maintaining sinus rhythm is almost zero
• Therefore, patients are kept in atrial fibrillation, and medication controls the ventricular response

Atrial Fibrillation

• The heart rhythm is irregularly irregular
• In V1, there are fibrillation waves that resemble sawtooth patterns, which are characteristic of atrial flutter
• It is not atrial flutter
• In the lower leads (II, III, and aVF), there are no sawtooth patterns
• Atrial flutter would exhibit a regularly irregular rhythm (alternating between two different RR intervals)
• Curved ST depressions (in II, III, aVF, V6) suggest the use of digoxin, which patients with AF often take
• This is coarse atrial fibrillation
• The amplitude of fibrillation waves in V1 is >0.5mm

Atrial Fibrillation

• The heart rhythm is irregularly irregular
• In lead V1, there are fibrillation waves that resemble sawtooth patterns, which can also be seen in atrial flutter
• It is not atrial flutter
• In the lower leads (II, III, aVF), there are no sawtooth patterns
• Atrial flutter would show a regularly irregular rhythm (alternating between two different RR intervals)
• This is coarse atrial fibrillation
• The amplitude of fibrillation waves in V1 is >0.5mm

Multifocal Atrial Tachycardia

• The heart rhythm is irregularly irregular
• Frequency: 120/min (6-second rule)
• At least 3 P waves of different shapes (marked with blue arrows)
• This ECG shows only 3 leads V1-V3 (marked as C1-C3)
• The patient has chronic obstructive pulmonary disease
• Multifocal atrial tachycardia is very common in patients with lung disease
• which can lead to pulmonary hypertension and right heart overload (remodeling)
• This is not atrial fibrillation (each QRS complex is preceded by a P wave)

Atrial Fibrillation

• The heart rhythm is irregularly irregular
• This is atrial fibrillation with slow ventricular response
• Frequency <60/min (6-second rule)
• The patient is likely on medication to slow AV node conduction
• Digoxin
• Beta-blockers
• Calcium channel blockers
• Hypothermia can also slow AV conduction
• This is fine atrial fibrillation
• Amplitude of fibrillation waves in V1 is <0.5mm
• ST depressions and negative T waves in lateral leads (I, aVL, V5, V6) may be associated with
• ischemia
• digoxin

Atrial Fibrillation and Ashman’s Phenomenon

• The heart rhythm is irregularly irregular
• This is atrial fibrillation with a rapid ventricular response
• Frequency >100/min (6-second rule)
• In the continuous II lead, we see a long-short RR interval, followed by a different QRS complex
• This is aberrant conduction (Ashman’s phenomenon)
• The impulse is conducted to the ventricles at a time when a part of the ventricular conduction system is in the refractory period
• The impulse is blocked in this part
• Most commonly, it is blocked in the right bundle branch
• The right bundle branch has the longest refractory period
• On this ECG, 2 different QRS complexes show the left anterior hemiblock
• Because the impulse was blocked in the left anterior fascicle