OSYPKA PACE 203H, Инструкция по эксплуатации

Страница: 85 / 139

PACE 203H – Instructions for Use
5I-17-016X-B-20 85 / 139
the ventricular triggering period, also
known as the crosstalk sensing window,
and the remaining period of the A-V
Delay, in which a sensed event inhibits
the ventricular output. This remaining
period may be not extant if the sum of
ventricular blanking period and crosstalk
sensing equals the A-V Delay.
9.22.4.1 Ventricular Blanking Period
To prevent crosstalk, PACE 203H initi-
ates, after an atrial stimulus, a brief
ventricular blanking period. As a con-
sequence, any possible crosstalk from
the atrial pacing stimulus is masked, or
blanked, with respect to the ventricular
sensing circuitry.
The blanking period is of short duration
because it is important for the ventricular
sensing circuit to be returned to the
“alert” state relatively early during the A-
V Delay so that intrinsic ventricular
activity can inhibit the ventricular output.
9.22.4.2 Crosstalk Sensing Window
and Ventricular Safety Pacing
The crosstalk sensing window follows
the ventricular blanking period. From
then on, PACE 203H cannot differentiate
crosstalk from intrinsic ventricular
activity.
To prevent ventricular systole, PACE
203H delivers a ventricular stimulus if
either crosstalk or intrinsic ventricular
activity is sensed within 40 ms after the
termination of the blanking period. This
interval of 40 ms is referred to as the
crosstalk sensing window, and the
ventricular response to as ventricular
safety pacing. This ventricular pacing
stimulus is delivered early, that is,
100 ms after the atrial event. This cor-
responds to an abbreviated A-V Delay of
100 ms.
If the signal sensed is indeed crosstalk,
the paced ventricular stimulus at the
abbreviated A-V Delay prevents
ventricular asystole.
If, on the other hand, intrinsic ventricular
activity occurs during this 40 ms window,
the safety mechanism results in delivery
of a ventricular pacing stimulus within, or
immediately after, the intrinsic beat. This
delivery is safe because the ventricle is
refractory. Consequently, no depolari-
zation results from the ventricular stimu-
lus. Furthermore, the stimulus is too ear-
ly to coincide with ventricular repolari-
zation or a vulnerable period.
Crosstalk window and safety pacing are
designed to supplement the ventricular
blanking function to ensure that crosstalk
inhibition will not occur.
PACE 203H indicates ventricular safety
pacing after A-V crosstalk through a
short time interval between the blinking
of the LEDs corresponding to ventricular
sensing and pacing, respectively.
9.22.5 Premature Ventricular
Contraction (PVC)
PACE 203H assumes an extrasystole, or
premature ventricular contraction (PVC),
if it detects two ventricular events without
an atrial event in between. The detection
of a PVC is indicated in the ventricular
section of the upper display by the sym-
bol for an extrasystole (see Figure 14).