Biomedical Engineering Reference
In-Depth Information
on a zinc-mercury basis. Nickel-cadmium rechargeable
batteries also were used [4]. On average, the batteries required
replacing after the lapse of a year and a half because of exhaus-
tion. Syncope during second- and third-degree AV block was
the main indication that a pacemaker should be implanted.
R3
100k
R1
2M
15k
C2
R8
C1
1µ
R4
10k
R6
22k
10µ
R2
2,2k
OUTPUT
1.2
Design History
10k
R5
R7
100k
The implantation of the “on-demand” pacing mode was a
great step forward, preventing possible competitive pacing
that potentially could result in ventricular fibrillation. The
first devices were launched in the mid-1960s (Fig.
1.3
). The
principle was devised by B. V. Berkowitz. In the late 1960s,
the first dual-chamber pacing system with the possibility of
R wave inhibition was developed. In cases of sinus bradycar-
dia and AV conduction defects, the device paced in the atrium
and, after a time lag, in the ventricle. Upon detection of
intrinsic ventricle activity, it only paced in the atrium.
However, the AV-sequential, dual-chamber pacing mode was
not applied until the 1970s.
As a consequence of the introduction of a lithium cell, the
dimensions of the device could be reduced. Its electrochemi-
cal properties made it easier to estimate the time until battery
exhaustion and to schedule device replacement. The most
important property of lithium/halogen cells was, however, that
they did not produce any gases while being used and could be
sealed hermetically. In the mid-1970s, certain manufacturers
started using titanium cans instead of the original epoxy resin
seal plug. As a consequence of signal processing development,
filtration at the input to the sensing circuits was improved, and
the impact of electromagnetic interference was minimized [4].
The first noninvasively programmable pacemakers were
launched. These devices could be programmed only to a lim-
ited extent, providing several options for the adjustment of
pacing rate (frequency), pulse amplitude, and, in certain types,
sensitivity. Another achievement was the introduction of two-
way programmer-implant communication. Nevertheless, fully
communicating devices capable of measuring the parameters
of a pacing circuit were not produced until the 1980s. The pos-
sibility of programming pacing pulse parameters and individ-
ual settings of a device in accordance with an individual
patient's needs prolonged the longevity of the devices and
enabled the treatment of various arrhythmias. In 1974, the first
three-position code for designating pacing mode was devel-
oped by the Intersociety Commission on Heart Disease
Resources. The code corresponds to the first three positions of
the code used today. At that time, most pacemakers worked in
the VVI mode (Fig.
1.4
). Since the beginning of the 1980s,
dual-chamber pacing has been applied more often because of
technical innovations. The devices were capable of pacing and
sensing in both the atrium and the ventricle; naturally, they
allowed two-way programmer-device communication and
were multiprogrammable.
Fig. 1.1
Asynchronous pacemaker circuit (Used with permission of
V. Bicik Research Institute for Medical Electronics and Modelling,
Prague, Czechoslovakia )
Fig. 1.2
Epoxy resin pacemaker
cardiac activity (but without the possibility of pacing inhibi-
tion) and allow modification of the pacing pulse amplitude,
measurement of the impedance, etc. The connection of the
external device and the implanted lead, however, proved to
be problematic because the percutaneous insertion of the
lead connected to the external device possessed a risk of
infection [ 10 ] .
First-generation implantable pacemakers only provided
asynchronous pacing, that is, they disregarded the intrinsic
cardiac activity (Fig.
1.1
). The output energy of pacing pulses
was higher than required. At that time, pacing at 70-80 pulses
per minute, voltage of around 5 V, and pulse width of 1.5 ms
was considered appropriate. Epoxy resin was chosen as a bio-
compatible material with which to plug the seal (Fig.
1.2
).
The first leads were epimyocardial, when the implantation
required a left-sided thoracotomy. The material of the leads
was Elgiloy alloy, which the Elgin Watch Company made use
of in balance wheels for mechanical watches. In addition, sili-
con transistors became widespread and enhanced the reliabil-
ity of circuits. Energy was supplied by electrochemical cells
