Biomedical Engineering Reference
In-Depth Information
Table 10.1
NASPE/BPEG de fi brillator codes [ 71 ]
Position
I
II
III
IV
Category
Shock chamber
Antitachycardia pacing chamber
Tachycardia detection
Antibradycardia pacing chamber
Letters
0 - None
0 - None
E - Electrogram
0 - None
A - Atrium
A - Atrium
H - Hemodynamic
A - Atrium
V - Ventricle
V - Ventricle
V - Ventricle
D - Dual (A + V)
D - Dual (A + V)
D - Dual (A + V)
Table 10.2 Example of ventricular detection zone con fi guration [ 82 ]
Zone con fi guration
VT-1 zone
VT zone
VF zone
1 zone
-
-
200 beats/min
2 zones
-
160 beats/min
200 beats/min
3 zones
140 beats/min
160 beats/min
200 beats/min
As a rule, as many as three VT zones may be programmed;
one of them may be programmed as a monitoring zone (with-
out a therapy, only for tachycardia diagnostic recording). For
each zone, a separate therapy prescription can be set up.
They are designated according to expected tachycardia (e.g.,
VT-1, VT, and VF). The zone setting is interrelated with
basic bradycardia parameters. The lowest VT zone threshold
value must be higher by a determined difference than the
maximum tracking rate, maximum sensor rate, and lower
rate limit parameters.
The ICD device must be capable of distinguishing between
several types of ventricular arrhythmias. Ventricular
fibrillation (VF) is a very fast rhythm with a low amplitude
and irregular cardiac intervals. VT is slower compared with
VF, with regular intervals. Supraventricular tachycardia is a
fast rhythm originating in atria; the rhythm is not indicated
for a ventricular therapy. Theoretically, atrial arrhythmia can
also be achieved by a shock applied between the lead proxi-
mal defibrillation electrode and the device can. Nevertheless,
this method is rarely applied in practice because it is painful
to a fully conscious patient. After delivery of therapy, the
ICD must evaluate the patient's rhythm again, and, in the
case of persisting arrhythmia, apply another therapy. Even
after the termination of the event, the device must continue
monitoring possible recurrence of tachycardia.
Steps to detect VT are as follows:
Initial detection
Fig. 10.1
X-ray image of an implantable cardioverter-de fi brillator
10.2
Tachycardia Detection
The application of appropriate treatment depends on a pre-
cise classification of the patient's rhythm. The ICD system
evaluates the heart rhythm based on individual cardiac cycles.
After a sensed event, the cycle length is measured and com-
pared with programmed detection parameters. Refractory
periods, together with noise windows, may eliminate sensing
of signals other than physiological ones and prevent the
delivery of potentially undesirable therapy. Atrial refractory
periods in DDD(R) and DDI(R) modes, right ventricular
refractory periods after a right-ventricle sensed event or after
charging capacitors, and refractory periods after shock may
be nonprogrammable.
A VT therapy zone is a range of heart rates in a frequency
domain delimited by at least one programmed VT threshold.
A programmed VT threshold value is a value to which the
ICD compares each sensed cardiac cycle period (Table 10.2 ).
Recon fi rmation
Redetection and detection after shock
10.2.1 Initial Detection
Criteria for initial detection of VT consist mainly of pro-
grammable parameters for the detection zone threshold rate
and duration. The detection criteria may also be extended
 
Search WWH ::




Custom Search