michael s
(Michael S)
#1
88 How do I manage the patient with an ICD?
Roy M John
An implantable cardioverter defibrillator (ICD) serves as prophy-
laxis against sudden collapse and death from rapid ventricular
arrhythmias. In general, all ICDs sense the heart rate and provide
anti-tachycardia pacing or deliver synchronised (cardioversion) or
unsynchronised (defibrillation) shocks. Some of the modern ICDs
also incorporate dedicated pacing function; patients with heart
block or sinus node disease may be dependent on these devices just
like any patient with an implanted cardiac pacemaker.
Like pacemakers, ICDs have to be checked by telemetric
interrogation at periodic intervals to confirm integrity of the lead
systems and proper function of ICD components including
adequacy of battery voltage. Reprogramming of the various
parameters that govern pacing, arrhythmia detection and therapy
may be necessary from time to time. Such routine follow up,
usually undertaken at established arrhythmia centres, should
occur at 3 to 6 monthly intervals in the absence of major inter-
current events. Some issues specific to this group of patients can
be summarised as follows:
1. Avoid rapid heart rates
In its basic form, arrhythmia detection algorithms of ICDs rely on
a programmed heart rate threshold. Once this is exceeded for a
defined period of time, the device may deliver therapy
irrespective of whether the arrhythmia is of ventricular or supra-
ventricular origin. In a ventricular-based ICD, the shock energy
vector is designed primarily to encompass the ventricles.
Consequently, atrial arrhythmias may fail to convert such that
multiple inappropriate ICD shocks may result. Further, if anti-
tachycardia pacing is delivered in the ventricle for an atrial
arrhythmia, ventricular arrhythmias may be provoked creating a
pro-arrhythmic situation. The newer ICDs incorporate atrial
sensing to improve arrhythmia discrimination but it must be
remembered that any algorithm that improves specificity for
ventricular arrhythmia will entail some loss of sensitivity.
Cognisant of the above, it is imperative that atrial arrhythmias are
adequately treated in these patients, particularly the paroxysmal
