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The real clinical usefulness of new generations of
automatic cardioverter defibrillators, provided with dual chamber pacing-sensing functions
and dual chamber arrhythmias detection algorithms, at the moment, is not evaluable cause
of their very recent availability.
First experiences with such devices1-2 allow the
management of prospective clinical studies designed to assess the real influence on
efficacy and safety and on sudden and non sudden mortality rates.
At the moment only retrospective studies are possible, in order to identify the
population that would benefit of such new functions.
A quantitative evaluation of patients in need of a dual chamber implantable
defibrillator is not easy and it requires the following information:
* population of patients that would benefit from atrial sensing in device detection
specificity enhancement
* population of patients that would benefit from VVD pacing in comparison with VVI
pacing modality in presence of AV block
* population of patients that would benefit from atrial pacing in case of sinus
dysfunction or drug induced sinus bradycardia
* atrial pacing efficacy assessment in myocardial electrical stability and atrial
arrhythmias prevention enhancement.
ICD patients with atrial arrhythmias history are around 20-30% and they represent the
majority of patients that experienced inappropriate interventions3-8:
in this situation atrial sensing, if flanked to "stability" and
"onset" criteria, could strongly increase device specificity in arrhythmias
detection. These two criteria allowed a reduction in non appropriate therapies3-8 but sometimes not sufficiently to avoid drug
treatments based on sotalol/amiodarone or radiofrequency AV node ablation10.
In these cases atrial pacing could be useful in order to achieve a better haemodynamic
stability, compensating bradycardiac effect of amiodarone, sotalol or other beta-blockers
and to achieve a better electrical atrial stability, potentially reinforced by other drugs
use11.
Moreover atrial sensing showed its efficacy in ventricular tachycardias detection
specificity enhancement when flanked to the well known "stability" and
"onset"1-2 inside full dual chamber
architecture-based detection algorithms12.
Dual chamber pacing shows clear advantages in haemodynamic performance with important
consequences on patients' life quality and duration.
Sudden death prevention doesn't lenghten life in patient with severely compromised
left ventricular function; in this case it's commonly accepted the statement that
defi-brillator determines only a short time shift from sudden death towards non sudden
death13-15. A left ventricular function enhancement
based on dual chamber pacing could decrease non sudden death based on mortality rate: this
positive effect, added to the well known efficacy of defibrillator in sudden death
prevention would lenghten life duration more consistently.
In addition it's clear that defibrillator implantation candidate patient with heart
failure and pacemaker implant indications would much more benefit from dual chamber pacing
modality. Anyway sequential pacing modality usefulness in patient characterized by normal
chronotropic response has to be clearly demonstrated.
Many clinical studies, but with methodological limitations, showed dual chamber
modality benefits in heart failure patients refractory to medical therapy16-21.
Dual chamber pacing, with atrioventricular delay ECO based optimization, in a
restricted population with dilated cardiomyopathy, diastolic mitralic insufficiency and
ejection fraction less than 25%, showed quality of life and cardiac output enhancement
after 3 months of follow-up24.
In any case the severe cardiac pathological pattern characterizing such categories of
patient could be complicated after defibrillator implant by sinus dysfunction or AV block:
in addition antiarrhythmic drugs as sotalol or amiodarone, usually prescribed, could
determine a marked sinus bradycardia.
In conclusion atrial sensing may further decrease ICD inappropriate intervention
incidence, albeit it is questionable if this favorable feature could offset the more
complex dual lead system; however, the advantage of atrial sensing may be obtained by
atrio-ventricular single lead technology avoiding the additional lead. This may also be
the solution for cases with A-V block and normal sinus node function. Dual chamber ICD is
suitable for patients who present at implantation time pacing indications or if the
addition of drugs, such as beta-blockers or amiodarone, which may determine chronotropic
incompetence, at rest and during exercise, may be predicted. The purpose of DDD pacing for
heart failure patients is to give sufficient chronotropic competence, an optimal A-V
sequential timing and a greater electrical stability. To date the prophylactic use of dual
chamber ICD in heart failure patients without pacing indications is still questionable.
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