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In order to synthetize past decade technologic
evolution of implantable cardioverter defibrillator device, since its first appearance in
clinical therapeutic application and also to draw potential future developments, it's
helpful to define the main analysis and description criteria of such a sophisticated
device.
It's also necessary and profitable to underline the deep cross-correlation, among
apparently distinct and separate technologic aspects, leading to heavy limitations in
device evolution.
The main and first distinction to do is relative to hardware and software
defibrillator technology.
Following this basic criterion it's possible to identify the principal areas involved
in technologic evolution (Fig. 1).
 
Fig. 1
Considering hardware area, device can and defibrillation leads represent the two
elements characterizing the system under the physical point of view. Both of them have
traced a clear evolution trajectory marked by size reduction: device volume and weight
have been reduced down to figures allowing easy to perform and patient comfortable
pectoral site implantations; on the other side defibrillation lead diameter, dimension and
flexibility have been enhanced, greatly simplifying lead system positioning procedures.
Considering the second technologic area, the software one, the most important aspects
are: arrhythmias therapeutic approach, arrhythmias detection criteria, pacemaker and
Holter function.
Arrhythmias therapy evolved from only shock defibrillators towards tiered
therapy-based implantable cardioverter defibrillators: at the moment therapeutic approach
reached the top if we consider safety, efficacy and flexibility of programmation, this
last feature allowing a total patient ventricular arrhythmia-based customization of the
device. Next step has been to design devices provided with therapeutic tools dedicated to
treat also atrial arrhythmias in order to make available a dual implantable cardioverter
defibrillator. Both cardiac chambers could be treated with such devices and positive
effects will be surely visible not only under the therapeutic point of view, but also
considering ventricular tachycardias detection enhancement deriving:
- firstly from atrial arrhythmias stop through appropriate and progressive therapy
(with ventricular therapeutic back up in case of induction of ventricular life-threatening
arrhythmias);
- secondly from atrial arrhythmias recurrence reduction by means of atrial pacing
algorithms of prevention.
Arrhythmias detection approach evolved from ventricular signal-based criteria (rate,
stability, onset and morphology to list only the most common ones) towards full dual
chamber architecture-based algorithms with important enhancement in sensitivity and
specificity performances.
Pacemaker function available in implantable defibrillators evolved from single chamber
to dual chamber pacing modality. Last generation of defibrillators expresses now a
technologic synthesis of two decades and a half of industrial and clinical experience in
pacing field: reliable and safe algorithms, as mode switching ones, rate responsive
function and other software tools, as the well known atrial arrhythmias prevention pacing
algorithms in clinical evaluation, are and will be soon available in defibrillators.
In addition more and more sophisticated and enlarged Holter function have been
introduced in implantable defi-brillators. In the next future not only memory size will be
important but also software tools, loaded on the programming system, able to manage
enormous quantity of information and able to perform automatic interpretation of such
amount of stored data: very positive results, encouraging this technologic evolution
project, have been already assessed by studies applied to pacemaker Holter memories.
In conclusion the next very close future is represented by a fully integrated
implantable defibrillator system: the dual DDD defibrillator.
Besides this consideration, in case of positive results deriving from present and
future clinical trials designed to prove a positive, real and enlarged effect of
prophylactic defibrillator implantation, technologic development in this field will be
necessarily marked by the birth of a second group of devices: the low cost and highly
sized reduced devices, able to deliver a very limited number of shocks and able to prevent
not previously documented sudden death episode. This new type of defibrillators would be
replaced after the first life-threatening ventricular arrhythmia episode positively
reduced: they will represent for the patient not only a real protection for their life but
also a bridge towards more sophisticated device when implant indication has been
documented.
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