| 1. Atrial
fibrillation, with a fast ventricular rate mediated
by a DDD pacemaker. You can see that all the
QRS complexes are preceded by spikes (the stimulation
by pacemaker). This irregular ventricular stimulation
is due to the sensing of chaotic atrial activity
(atrial fibrillation) (Image 1)
2. Atrial fibrillation, with atrioventricular
blockade and a VVI pacemaker. The pacemaker is
programmed to pace to 75bpm. The atrial activity
is not sensed by the pacemaker and therefore
does not influence the frequency of stimulation
(Image 2)
The pacemaker with atrial sensing (DDD and others)
can detect the electric activity of the atrium.
If this accelerates, it responds by increasing
the frequency of ventricular pacing, as is the
physiological response during exercise. Patients
with sustained atrial fibrillation should not
have this type of pacemaker implanted because
it will stimulate the ventricles to an inappropriately
high rate, and may lead to cardiac insufficiency
or myocardial ischaemia. If a patient with a
DDD pacemaker falls into atrial fibrillation
they can suffer an inappropriate acceleration
of ventricular frequency (Fig 1). If QRS complexes
are preceded by spikes they are stimulated by
the pacemaker and are not conducted through the
AV node; in this case beta blockers, diltiazem
and digoxin are not effective in controlling
rate. Electrical or pharmacological cardioversion
can be effective. The pacemaker is reprogrammable
externally (without opening skin). If a patient
with a pacemaker with atrial sensation falls
into atrial fibrillation, the system can be reprogrammed
to VVI, normalising the cardiac frequency if
the tachycardia was mediated by that lead (Fig
2). If a magnet is available for reprogramming
(as is used in ED and ICU) it can be placed over
the generator. The atrial sensor will not function
while the magnet is over it and the cardiac frequency
will be normalized (Fig 2).
Authors:
José Luis Morales Rull
Servicio Medicina Interna - Hospital Clínico Universitario - Zaragoza
Amalio Carmona Aymat
Servicio de Cardiología - Hospital Clínico Universitario - Zaragoza
Translation: Kelly
Watt |
