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- AF, atrial fibrillation
- CAD, coronary artery disease
- DC-ICD, dual chamber implantable cardioverter-defibrillator
- DCM, dilated cardiomyopathy
- EF, ejection fraction
- ICD, implantable cardioverter-defibrillator
- IST, inappropriate shock therapy
- LV, left ventricular
- MI, myocardial infarction
- NYHA, New York Heart Association
- SC-ICD, single chamber implantable cardioverter-defibrillator
- SVT, supraventricular tachycardia
- VF, ventricular fibrillation
- VT, ventricular tachycardia
Implantable cardioverter-defibrillators (ICDs) are standard treatment for both secondary and primary prevention in patients with malignant ventricular arrhythmias.1,2 Inappropriate shock therapy (IST) occurs in a significant proportion of ICD patients, despite newer generation devices and algorithms specifically employed to try and eliminate this.3
The frequency of IST in patients implanted with cardioverter-defibrillators at this institution over a 17 year period from 1984 to 2001 was assessed. Predictive factors of IST were assessed, as was the susceptibility of certain subgroups to IST. Also, newer dual chamber devices were examined to see if they reduced IST.
METHODS
We retrospectively analysed data from 171 patients. Each patient had an ICD capable of storing electrograms that met the programmed criteria for detection (that is, fell within a ventricular tachycardia (VT) or ventricular fibrillation (VF) therapy zone). Full data regarding delivered therapy were available in 155 patients. We analysed stored electrogram data from the ICD. Clinical assessments were made by studying ECG data and inpatient records from the time of hospitalisation, to assess whether therapy was appropriate. Therapy was deemed inappropriate when delivered for rhythms that were not VT or VF. A probability value of p < 0.05 was considered significant.
RESULTS
IST occurred in 22 patients (14%). Of these, 18 received IST for atrial arrhythmias (flutter/fibrillation) or sinus tachycardia. In the …