Biomedical Engineering Reference
In-Depth Information
5
Pacing Modes
5.1
A00 Mode
Pacing mode offers a basic overview of the therapeutic
possibilities of certain types of devices. On the basis of the
number of physically attached leads, single-chamber and
dual-chamber modes are determined. The programmability
of the device also allows dual-chamber devices to be oper-
ated as single-chamber devices (although the reverse is, of
course, impossible).
This chapter information about programmable modes
available with pacemakers. Explanation of North American
Society of Pacing and Electrophysiology (NASPE)/British
Pacing and Electrophysiology Group codes used in pacemak-
ers is shown in Table
5.1
. At positions I and II there are
identification of paced and sensed heart chambers. At posi-
tion III there is the mode of response to sensed intrinsic heart
action (P wave, R wave, or both). Char I (inhibited) means
that when intrinsic heart activity is sensed in the heart cham-
ber, no pacing pulse will be generated during the actual cardiac
cycle. Char T (triggered) means that a pacing pulse is gener-
ated in reaction to intrinsic heart activity. At position IV there
is identification of rhythm modulation (adaptive-rate pacing).
The fifth position indicates whether multisite pacing is possi-
ble. Multisite pacing is defined as using of more than one site
in a given heart chamber for pacing. For explanation of other
North American Society of Pacing and Electrophysiology/
British Pacing and Electrophysiology Group codes, see
Bernstein et al. [ 31 ] . Figure
5.1
may help clinicians program
the most appropriate pacing mode for a specific patient.
Pacing pulses are delivered asynchronously to the atrium at
the lower rate limit (LRL) (Fig.
5.2
). Intrinsic heart activity
(P wave) does not inhibit or trigger pacing in the atrium. The
A00 mode is either directly programmable or operative with
the use of a magnet in AAI and AAT modes. The asynchro-
nous A00 mode may be used intraoperatively to reduce the
likelihood of inhibition during electrocautery [ 32 ] .
5.2
AAI(R) Mode
In the AAI(R) mode, sensing and pacing occur only in the
atrium (Fig.
5.3
). In the absence of sensed events, pacing
pulses will be delivered to the atrium at the programmed
LRL (AAI) or at a rate indicated by the sensor (AAI[R]).
A sensed P wave or a paced atrium event causes the pace-
maker's escape interval to reset [ 32 ] .
5.3
AAT Mode
In the AAT mode, pacing pulses will be delivered to the
atrium at the LRL in the absence of sensed events (Fig.
5.4
).
Sensed events trigger the atrial pulse and resets the pace-
maker escape interval. Using the AAT mode outside of a
diagnostic setting is not recommended because of the poten-
tial for triggered pacing in response to oversensing [32].
The possibility of programing pacing mode is limited
according to the particular pacemaker model. Within VVI(R),
AAI(R), SSI(R), V00(R), A00(R), and S00(R), adaptive-rate
pacing is combined with single-chamber pacing. Within
DDD(R), DDI(R), and D00(R) modes, adaptive-rate pacing
is combined with dual-chamber pacing. Other available pac-
ing modes are DDD, DDI, D00, VDD, VVI, AAI, SSI, V00,
A00, S00, VVT, AAT, and SST. The 0D0, 0S0, and 000
modes generally are programmable as temporary modes and
are used for diagnostic purposes [ 32 ] .
5.4
V00(R) Mode
Pacing pulses will be delivered asynchronously to the
ventricle at the LRL (V00) or at the sensor-indicated rate in
the V00(R) mode. Spontaneous ventricular events (R wave)
do not inhibit or trigger pacing in the ventricle. The V00
