Diagnostics and Therapy by the ICD Better than the Cardiologist

From the time of introduction of the Implantable Cardioverter Defibrillator (ICD), the device has evolved from a simple shock-box to a complete arrhythmia management device. Diagnostics or interpretation of what the defibrillator had done with the patient and his arrhythmias has always been a matter of concern for the cardiologist [1]. In the beginning, the nonprogrammable devices were limited to shock delivery, and it was only possible to assess the charge time and to read the number of delivered shocks (Figure 1.1).

Advances in diagnostic information have paralleled the improvements in arrhythmia treatment (pacing, antitachycardia pacing, atrioversion). The current generation of ICDs offers an array of diagnostic information, including stored electrograms. Analysis of this diagnostic information has not only improved the management of patients, but also contributed to an increased understanding of triggers precipitating device therapy. It becomes evident that the amount of data available in a device will be extremely helpful to the experienced cardiologist to understand the arrhythmia, the involved mechanism, and the underlying disease. Physiological information derived from measurements like thoracic impedance, lead tension, and oxygen saturation will become available and will even change our management of heart failure patients. It is clear that device information has to be reliable; therefore it has to be studied, understood, and often corrected. Cardiologists should not solely rely on information as provided by the manufacturer, but be prepared to teach other physicians (who are not electrophysiologists), nurses, and technicians. They should be able to engage in a discussion with the industry at a high level. We hope that this book will be a contribution to be successful in this area.

Historical Perspective of Diagnostic Information in ICDs

In the first-generation devices, the definition of "appropriate" therapy relied on the clinical history of the patient, the presence or absence of hemody-namically significant symptoms, or concomitant ECG monitoring. Diagnostic information remained limited after the introduction of programmable devices (Figure 1.2).

Ventak 1500
Figure 1.1. Read-out of the device, using a doughnut-magnet, which allowed capacitor reformation. Via audible tones synchronicity with the R-wave was assessed (AID and AICD, Intec; later Ventak 1500 series, CPI).

The second-generation ICDs had recording of numerical RR intervals, often tabular, sometimes with device activity markers. This storage allowed analysis of the rate of the arrhythmia preceding and following ICD therapy. Differentiation of arrhythmias was based on the regularity of RR intervals. Irregular RR intervals suggested atrial fibrillation (AF), while regular RR intervals could indicate sinus tachycardia, arial flutter, or atrial tachycardia as well as ventricular tachycardia (Figure 1.3).

Appropriate ICD therapy for ventricular arrhythmias without hemodynam-ically significant symptoms was soon demonstrated in patients [2, 3]. With third-generation devices, the most significant advance in diagnostic information was the storage of intracardiac electrogram recordings (Figure 1.4). This diagnostic information included recording of RR intervals preceding and following the arrhythmia, and stored electrograms with real-time marker channels of arrhythmias triggering ICD therapy. It became clear that this bit of information would be helpful in the interpretation of clinical data.

The Diagnosis of Ventricular Tachycardia: A Continuing Story with a Happy End?

The manifestation of a regular broad complex tachycardia on the electrocardiogram can be due to ventricular tachycardia or supraventricular tachycardia with aberrant conduction. For the accurate differential diagnosis of a broad

The Diagnosis of Ventricular Tachycardia: A Continuing Story with a Happy End? 3

The Diagnosis of Ventricular Tachycardia: A Continuing Story with a Happy End? 3

Ecg With Aberrant Conduction
Figure 1.2. EP test data and pulse generator data printouts of one of the first programmable ICDs (Ventak P 1600, Guidant).

complex tachycardia, several famous cardiologists have developed diagnostic algorithms [4-6]. Most of these diagnostic algorithms are based on features of the QRS complex, including QRS width, morphology in the precordial leads and axis in the frontal plane, and features of atrioventricular dissociation like the presence of P waves independent of QRS complexes, fusion, or capture beats. The diagnostic algorithms implement these features into a step-by-step diagnostic hierarchy. Despite these algorithms, misdiagnoses are still common [6]. A major limitation of these diagnostic algorithms is imperfect

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