13th International Congress
THE "NEW FRONTIERS"
OF ARRHYTHMIAS 1998

January 24-31, 1998
Marilleva, Trento, Italy

S-165

Dual-chamber ICD indications:
present and future

P.E. Vardas.
Cardiology Department, University Hospital of Heraklion, Crete, Greece

Automatic implantable cardioverter defibrillator devices undoubtedly represent one of the major technological breakthroughs in the last two decades for the treatment of cardiac rhythm disorders. Today's devices are capable of low energy cardioversion, antitachycardia pacing and defibrillation, together with antibradycardia pacing and sensing in the ventricle. The recording of the internal electrogram and the ability of these devices to function as an internal Holter monitor allows the cardiologist to check on the device's performance and to make any necessary adjustments in the programming.

However, this self checking capacity has revealed one of the main limitations of ICDs, namely, their lack of specificity in the detection of ventricular tachycardia. False pos-itive detection of atrial tachyarrhythmias with a fast ventricular response as ventricular tachyarrhythmias can lead to inappropriate electrical therapy. In fact, such inappropriate therapy for documented non-ventricular rhythm has been documented in up to 41% of all patients treated with an ICD, sometimes with serious complications.

The vast majority of arrhythmia episodes leading to inadequate defibrillator therapy are caused by paroxysmal atrial fibrillation (AF) with a fast ventricular response. Although many algorithms have been developed to deal with this arrhythmia, they all suffer from the limitation of being based only on ventricular sensing, which leads to deficiencies in accuracy and specificity. Thus, dual-chamber sensing is an obvious approach to the problem. A device with the ability to sense and pace in both ventricle and atrium, as well as performing cardioversion and defibrillation in the ventricle, offers clear advantages over conventional ICDs¹. The dual-chamber ICDs available at present, apart from delivering electrical therapy to the ventricle, are also capable of pacing and sensing in both ventricle and atrium. Some dual-chamber ICD devices can also deliver defibrillatory shocks to the atrium.

The electrical benefits of dual-chamber ICD systems are as follows²:

* they allow both atrial and atrioventricular pacing;
* they can discriminate better between supraventricular and ventricular arrhythmias^3,4;
* interactions between dual-chamber pacemaker and ICD are reduced;
* atrial pacing may be used to prevent AF;
* atrial or dual-chamber defibrillation are both possible.

It is also possible that atrioventricular pacing may improve the haemodynamic function in patients with compromised left ventricular function.

Key Words

Implantable cardioverter defibrillator – new perspectives  
dual chamber ICD, low energy cardioversion, antitachycardia pacing, defibrillation, antibradycardia pacing, atrial pacing, atrioventricualr pacing, atrial sensing-pacing, paroxysmal AF, ventricualr tachycardia/fibrillation, sudden cardiac death, R