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Fusion and Pseudofusion Beats during Pacing

Ventricular fusion beat and Ventricular pseudofusion beat pacemaker activity

Ventricular Extrasystole and Own QRS Beat
Fusion beat during pacing
Pseudofusion Beat during Pacing

Ventricular Extrasystole and Own QRS Beat

Single chamber pacemaker, VVI mode

Ventricular extrasystole and own QRS complex

They have a different shape during pacing

VVI pacemaker has one electrode in the right ventricle

V - ventricular pacing
V - ventricular sensing
I - positive sensing inhibits pacing
The pacemaker senses its own chamber's electrical activity

Own electrical activity "turns off" pacing

Pacemaker VVI mode pacing, paced QRS complexes, ventricular extrasystole, normal QRS, Lower rate limit

VVI pacemaker

Single-chamber pacemaker in VVI mode
Stimulated QRS complexes (2,3,6,7)

Before each QRS, there is a pacing artifact (vertical line)
The pacemaker has a defined escape interval (e.g., 1000ms)

If within 1000ms from the previous QRS no own QRS occurs, ventricular pacing is activated
The escape interval is sometimes referred to as the Lower rate limit (LRL)

Own QRS complex (1,5)

Occurred before 1000ms from the previous QRS, thus inhibiting pacing (no pacing artifact)

Ventricular extrasystole (4)

Occurred before 1000ms from the previous QRS, thus inhibiting pacing (no pacing artifact)

Each QRS complex (stimulated, own, extrasystole) has a different shape

Because the ventricles are depolarized from different foci

Fusion beat during pacing

ECG pacemaker fusion beat

Fusion beat

Occurs when the ventricles are simultaneously activated by 2 impulses

One impulse from the pacemaker electrode
The other impulse is natural

T wave after a fusion beat

Is different from the T wave after a natural QRS complex

Fusion beat (without pacemaker) is a sign of ventricular tachycardia

One impulse is supraventricular
The other impulse is from an ectopic focus in the ventricle

Pacemaker VVI mode, fusion beats, pseudofusion beats

VVI pacemaker

Single chamber pacemaker in VVI mode
The last 3 QRS complexes are paced QRS complexes

A QRS complex follows the pacing artifact

Fusion beat - F

They are usually narrower than a normal paced QRS complex

Because the ventricles depolarize from 2 foci faster

They have variable shapes

They are always different from

normal paced QRS complexes
natural QRS complexes without pacing

The first 4 QRS (stars) are pseudo-fusion beats

Pseudofusion Beat during Pacing

ECG pacemaker pseudofusion beat

Pseudofusion Beat

It is a natural QRS complex

Which is overlaid by a pacing artifact

The pacing artifact occurs during the refractory phase of the ventricles

Therefore, the ventricles ignore the pacing

T wave after a pseudofusion beat

Is the same as the T wave after a natural QRS complex

Timing of a Pseudofusion Beat:

The pacing artifact occurs at the end of the LRL interval

But just before the LRL, a natural QRS begins to form

The ventricular lead senses the natural QRS (positive sensing)

Too late (because the ventricular pacing has already occurred)

Pacemaker VVI mode, fusion beats, pseudofusion beats

VVI Pacemaker

Single-chamber pacemaker in VVI mode
The first 4 QRS are pseudofusion beats

Natural QRS complexes are overlaid by the pacing artifact
The artifact occurs just after the natural ventricular activation, thus not affecting the shape of the QRS

On the ECG, however, the natural QRS without the pacing artifact is not recorded

The last 3 QRS are paced QRS complexes

Each QRS complex follows a pacing artifact

Fusion Beat - F

Typically, these are narrower than a normally paced QRS complex

Because the ventricles are depolarized faster from 2 foci

They have variable shapes

Always different from

normally paced QRS complexes
natural QRS complexes without pacing

Sources

ECG from Basics to Essentials Step by Step
litfl.com
ecgwaves.com
metealpaslan.com
medmastery.com
uptodate.com
ecgpedia.org
wikipedia.org
Strong Medicine
Understanding Pacemakers

Fusion and Pseudofusion Beats during Pacing

Ventricular fusion beat and Ventricular pseudofusion beat pacemaker activity

Ventricular Extrasystole and Own QRS Beat
Fusion beat during pacing
Pseudofusion Beat during Pacing

Ventricular Extrasystole and Own QRS Beat

Ventricular extrasystole and own QRS complex

They have a different shape during pacing

VVI pacemaker has one electrode in the right ventricle

V - ventricular pacing
V - ventricular sensing
I - positive sensing inhibits pacing
The pacemaker senses its own chamber's electrical activity

Own electrical activity "turns off" pacing

Single chamber pacemaker, VVI mode

Pacemaker VVI mode pacing, paced QRS complexes, ventricular extrasystole, normal QRS, Lower rate limit

VVI pacemaker

Single-chamber pacemaker in VVI mode
Stimulated QRS complexes (2,3,6,7)

Before each QRS, there is a pacing artifact (vertical line)
The pacemaker has a defined escape interval (e.g., 1000ms)

If within 1000ms from the previous QRS no own QRS occurs, ventricular pacing is activated
The escape interval is sometimes referred to as the Lower rate limit (LRL)

Own QRS complex (1,5)

Occurred before 1000ms from the previous QRS, thus inhibiting pacing (no pacing artifact)

Ventricular extrasystole (4)

Occurred before 1000ms from the previous QRS, thus inhibiting pacing (no pacing artifact)

Each QRS complex (stimulated, own, extrasystole) has a different shape

Because the ventricles are depolarized from different foci

Fusion beat during pacing

Fusion beat

Occurs when the ventricles are simultaneously activated by 2 impulses

One impulse from the pacemaker electrode
The other impulse is natural

T wave after a fusion beat

Is different from the T wave after a natural QRS complex

Fusion beat (without pacemaker) is a sign of ventricular tachycardia

One impulse is supraventricular
The other impulse is from an ectopic focus in the ventricle

ECG pacemaker fusion beat

Pacemaker VVI mode, fusion beats, pseudofusion beats

VVI pacemaker

Single chamber pacemaker in VVI mode
The last 3 QRS complexes are paced QRS complexes

A QRS complex follows the pacing artifact

Fusion beat - F

They are usually narrower than a normal paced QRS complex

Because the ventricles depolarize from 2 foci faster

They have variable shapes

They are always different from

normal paced QRS complexes
natural QRS complexes without pacing

The first 4 QRS (stars) are pseudo-fusion beats

Pseudofusion Beat during Pacing

Pseudofusion Beat

It is a natural QRS complex

Which is overlaid by a pacing artifact

The pacing artifact occurs during the refractory phase of the ventricles

Therefore, the ventricles ignore the pacing

T wave after a pseudofusion beat

Is the same as the T wave after a natural QRS complex

Timing of a Pseudofusion Beat:

The pacing artifact occurs at the end of the LRL interval

But just before the LRL, a natural QRS begins to form

The ventricular lead senses the natural QRS (positive sensing)

Too late (because the ventricular pacing has already occurred)

ECG pacemaker pseudofusion beat

Pacemaker VVI mode, fusion beats, pseudofusion beats

VVI Pacemaker

Single-chamber pacemaker in VVI mode
The first 4 QRS are pseudofusion beats

Natural QRS complexes are overlaid by the pacing artifact
The artifact occurs just after the natural ventricular activation, thus not affecting the shape of the QRS

On the ECG, however, the natural QRS without the pacing artifact is not recorded

The last 3 QRS are paced QRS complexes

Each QRS complex follows a pacing artifact

Fusion Beat - F

Typically, these are narrower than a normally paced QRS complex

Because the ventricles are depolarized faster from 2 foci

They have variable shapes

Always different from

normally paced QRS complexes
natural QRS complexes without pacing

Sources

ECG from Basics to Essentials Step by Step
litfl.com
ecgwaves.com
metealpaslan.com
medmastery.com
uptodate.com
ecgpedia.org
wikipedia.org
Strong Medicine
Understanding Pacemakers