• Heart Rhythm
• Ventricular Rhythm
• Ventricular Rhythm - Most Common Causes
• QRS Complex Width and Cardiac Rhythms
• ECG and Ventricular Rhythm
• Ectopic Focus Localization
• Frequency and Ventricular Rhythm

Heart Rhythm

Basic Heart Rhythms

• Heart rhythm is always determined by the site (sites) that generate 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
• It is the primary pacemaker
• Generates impulses with a frequency of: 60 - 100/min.
• Junctional Rhythm
• It is the secondary pacemaker
• Generates impulses with a frequency of: 40 - 60/min.
• Ventricular Rhythm
• It is the tertiary pacemaker
• Generates impulses with a frequency of: 20 - 40/min.
• Activates when:
• Impulses from the supraventricular area (SA node and AV junction) cease to reach the ventricles
• The ventricles outpace the supraventricular areas in generating impulses

Ventricular Rhythm - Most Common Causes

• Ventricles do not receive supraventricular impulses:
• Sinus arrest
• SA block III degree
• AV block III degree
• Ventricles receive supraventricular impulses with frequency < 40/min.:
• Sinus bradycardia (extreme)
• Junctional bradycardia
• AV block II degree (high grade)
• Hyperkalemia
• Beta-blockers
• Calcium channel blockers
• Digoxin toxicity
• Ectopic focus in the ventricles outpaces supraventricular impulses:
• Accelerated ventricular rhythm
• Ventricular tachycardia

Junctional Rhythm

• AV junction generates impulses with a frequency of: 40-60/min.
• The impulse from the AV junction spreads:
• to both the atria and the ventricles
• Ventricular vector points towards Lead II
• A narrow QRS complex forms
• Because the ventricles are activated quickly via the conduction system
• Atrial vector points towards the SA node
• Direction from Lead II
• A negative - retrograde P wave forms
• First, the ventricles are activated (QRS) and then the atria (negative P wave)
• On the ECG, it is a junctional rhythm

ECG and Ventricular Rhythm

• Frequency: 20 - 40/min.
• Wide QRS complexes (> 0.12s)
  • QRS complexes (depending on the location of the ectopic focus) have a shape:
  • Left bundle branch block
  • Right bundle branch block
  • Wide QRS complexes also occur with aberrant conduction
• Heart rate is regular (RR interval remains unchanged)
• The ventricular focus is not influenced by the sympathetic or parasympathetic nervous systems
• No analogy to respiratory sinus arrhythmia
• P waves are often absent; if a P wave reaches the ventricles, it may result in:
• AV dissociation
• Fusion beats
• Capture beats

Ectopic Focus Localization

• Active ectopic focus depolarizes both ventricles through the myocardium
• The principle is similar to
• Left Tawar's bundle branch block
• Right Tawar's bundle branch block
• If the ventricular vector points
• Toward the lead, a positive QRS complex is formed
• Away from the lead, a negative QRS complex is formed
• For basic localization of the focus, opposite chest leads V1 and V6 are used
• The localization of the focus is important in the differential diagnosis of wide complex tachycardia

Ectopic Focus in the Right Ventricle

• Negative QRS (V1)
• Vector points away from lead V1
• Positive QRS (V6)
• Vector points toward lead V6

Ectopic Focus in the Left Ventricle

• Positive QRS (V1)
• Vector points toward lead V1
• Negative QRS (V6)
• Vector points away from lead V6

Ventricular Rhythm

• Frequency: 27/min.
• Ventricular rhythm has a frequency of 20-40/min.
• Wide QRS complexes (> 0.12s)
• P waves are absent
• This indicates SA block IIIrd degree
• Often, a secondary pacemaker is activated - junctional rhythm
• In this case, the ventricular rhythm - tertiary pacemaker was activated

Ventricular Tachycardia

• Frequency: 160/min.
• Ventricular tachycardia has a frequency > 100/min.
• Wide QRS complexes (> 0.12s)
• P waves are absent
• Patients with ventricular tachycardia are often hemodynamically unstable, with a risk of ventricular fibrillation
• The heart stops functioning as a pump
• Requires urgent treatment (medication or defibrillation)

Ventricular Rhythm and AV Block III Degree

• Frequency 27/min.
• Wide QRS complexes (> 0.12s)
• Heart rate is regular (RR interval is constant)
• The ectopic focus is in the left ventricle (see image of RBBB)
• Positive QRS (V1)
• Negative QRS (V6)
• The ectopic focus is in the left ventricle in the area of the left anterior fascicle
• Because there is a presence of left posterior hemiblock
• On the ECG, there is an AV Block III Degree
• There is electrical isolation between the atria and ventricles
• The AV junction is interrupted
• Frequency of P waves is 65/min. (Continuous II lead)
• Impulses from the SA node are blocked at the AV junction
• AV Dissociation
• There are 2 independent pacemakers in the heart: (that generate impulses)
• SA node
• Ectopic ventricular focus
• P waves and QRS complexes are completely independent of each other