Fusion beat

Fusion Beat

A fusion beat is a type of cardiac arrhythmia that occurs when electrical impulses from two different sources combine to produce a single heartbeat. This phenomenon is most commonly observed in the context of ventricular tachycardia or ventricular pacing, where the heart's normal conduction system and an ectopic pacemaker or pacing device simultaneously activate the ventricles.

ECG showing a fusion beat

Mechanism

Fusion beats occur when there is simultaneous activation of the ventricles by two different impulses. One impulse originates from the heart's normal conduction system, typically the sinoatrial node or the atrioventricular node, while the other impulse comes from an ectopic focus or a pacing device. When these impulses meet, they can partially depolarize the ventricles, resulting in a hybrid or "fused" QRS complex on the electrocardiogram (ECG).

The appearance of a fusion beat on an ECG is characterized by a QRS complex that is intermediate in morphology between a normal QRS complex and a fully ectopic or paced QRS complex. This occurs because the ventricles are being activated by both the normal conduction pathway and the ectopic or paced pathway.

Clinical Significance

Fusion beats are significant in the diagnosis and management of certain cardiac arrhythmias. They are often seen in patients with ventricular tachycardia, where they can help differentiate between supraventricular tachycardia with aberrant conduction and true ventricular tachycardia. The presence of fusion beats suggests that there is some degree of normal conduction system involvement, which can influence treatment decisions.

In the context of cardiac pacing, fusion beats can indicate that the pacing device is functioning properly and that there is some intrinsic cardiac activity. This can be important for adjusting pacing settings and ensuring optimal device performance.

Diagnosis

The diagnosis of fusion beats is primarily made through careful analysis of the ECG. Clinicians look for QRS complexes that have a morphology intermediate between normal and ectopic or paced beats. The presence of fusion beats can be confirmed by observing changes in the QRS complex morphology during different phases of the arrhythmia or pacing.

Related Pages

• Cardiac arrhythmia
• Ventricular tachycardia
• Electrocardiogram
• Cardiac pacing
• Sinoatrial node
• Atrioventricular node