• Heart Rhythm
• Atrial Premature Contraction (APC)
• ECG and Atrial Premature Contraction
• Incomplete Compensatory Pause
• Complete Compensatory Pause
• Aberrant Atrial Extrasystole
• Atrial Extrasystoles - Classification
• Unifocal Atrial Extrasystole
• Multifocal Atrial Extrasystole
• Atrial Extrasystoles by Repetition

Heart Rhythm

Basic Heart Rhythms

• Heart rhythm is determined by the site (sites) that generates impulses with the highest frequency (overdrive suppression)
• There are 3 basic heart rhythms
• Sinus Rhythm (Impulses are generated by the SA node)
• Junctional Rhythm (Impulses are generated by the AV junction)
• Ventricular Rhythm (Impulses are generated by the Purkinje fibers in the ventricles)
• Sinus Rhythm is the physiological heart rhythm
• Because the sinoatrial (SA) node generates impulses with the highest frequency (overdrive suppression)
• The SA node is referred to as the primary pacemaker

ECG and Atrial Premature Contraction

• Abnormal ectopic P wave (has a different shape than the sinus)
• It is followed by a narrow QRS complex (< 0.12s)
• It may be obscured by a T wave
• In this case, it resembles a junctional premature contraction
• Retrograde (negative) P wave occurs:
• If the ectopic focus is at the AV junction
• It differs from junctional premature contraction by the PQ interval
• PQ interval < 0.12s - Junctional premature contraction
• PQ interval > 0.12s - Atrial premature contraction
• On the ECG, it appears earlier than the expected sinus P wave
• Incomplete compensatory pause
• APCs always reset the SA node
• Blocked APC
• If an APC occurs during the refractory phase of the AV junction
• It gets blocked in the AV junction
• An abnormal P wave without a QRS complex occurs

Atrial Premature Contraction and Incomplete Compensatory Pause

• PP (RR) interval with APC (36) is shorter than twice the PP (RR) interval without APC (2x20)
• Atrial Premature Contraction (APC)
• Occurs earlier than the expected sinus P wave (QRS complex)
• Narrow QRS complex (<0.12s)
• The P wave resembles the sinus P wave
• Because the ectopic focus is near the SA node, the atrial vector then has a similar direction

Ventricular Premature Contraction and Complete Compensatory Pause

• PP (RR) interval with VPC (42) is exactly twice the PP (RR) interval without VPC (2x21)
• Ventricular Premature Contraction (VPC)
• Occurred earlier than the expected sinus QRS complex
• Wide QRS complex (>0.12s)
• Indicated P wave just after the QRS
• VPC did not reset the SA node because VPC did not pass through the AV node

Sinus Rhythm Without Atrial Extrasystole

• The SA node generates impulses regularly (P waves), which are conducted to the ventricles (QRS complexes)
• LTR: Length of the refractory period of the Left Tawar bundle branch
• PTR: Length of the refractory period of the Right Tawar bundle branch
• The refractory period occurs shortly after an impulse passes through the conduction system
• During the refractory period, the conduction system does not conduct impulses

Aberrant Atrial Extrasystole

• The extrasystole (P´) occurred at a time when the left Tawar's branch is no longer in the refractory phase
• But the right branch is still in the refractory phase, causing the extrasystole to be blocked in the right Tawar's branch
• Therefore, the extrasystole (QRS complex) has a right Tawar's branch block shape

Aberrant Atrial Extrasystole

• The P wave of the atrial extrasystole has a different shape compared to the sinus P wave
• Incomplete compensatory pause
• The extrasystole occurred during the refractory period of the right Tawar's branch
• Therefore, the QRS has the shape of a right Tawar's branch block

Atrial Extrasystoles - Classification

• Atrial Extrasystoles by the number of ectopic foci
• Unifocal
• Multifocal
• Atrial Extrasystoles by frequency
• Isolated
• Bigeminy
• Trigeminy
• Quadrigeminy
• Couplet
• Triplet

Multifocal Atrial Extrasystole

• Multifocal (Polytopic) Atrial Extrasystole
• Atrial Extrasystole originate from multiple ectopic foci
• Atrial Extrasystole from each focus generates an extrasystole (P wave) of a different shape
• On the ECG, atrial extrasystoles (P waves) have different shapes

Multifocal Atrial Extrasystole

• On the ECG, there are 2 multifocal atrial extrasystoles
• Narrow QRS complex (<0.12s)
• Each Atrial Extrasystole is from a different ectopic focus, therefore:
• It has a different P wave
• It has a different coupling interval
• Distance between Atrial Extrasystole and the preceding QRS complex
• QRS complexes are the same because each supraventricular impulse activates the ventricles through the AV node
• If the heart rhythm is determined by only ectopic atrial extrasystoles without the SA node, it is:
• Multifocal atrial rhythm

Isolated Atrial Extrasystole

• Isolated Atrial Extrasystole appear on the ECG sporadically

Atrial Trigeminy

• Every third beat is an atrial extrasystole

Atrial Couplet

• 2 atrial extrasystoles in a row

Aberrant Atrial Extrasystole

• In the limb leads (aVL, aVF, II), the extrasystole is recorded with a wide QRS (>0.12s)
• It is not a ventricular extrasystole because there is a P wave before it
• Continuous lead II does not align parallel with the limb leads
• This is an aberrant atrial extrasystole
• Because there is a deformed P wave before the wide QRS complex
• Fusion beat is not expected, as it would have a sine P wave before the QRS
• The extrasystole is not recorded in the precordial leads (V1, V6)
• Thus, it is not possible to precisely determine if it is an aberrant block of the left or right Tawar's bundle