Non-invasive Programmed Stimulation to Identify High-risk Patients With Implanted Cardioverter-defibrillator

Some studies have shown that factors predicting ventricular tachycardia (VT) or ventricular fibrillation (VF) recurrences and consequently ICD interventions, include patient's age, New York Heart Association class heart failure, left ventricular ejection fraction (LVEF), the presence of atrial fibrillation (AF), the QRS complex width, and the status of renal function. However, the accuracy of these parameters is limited and other variables that may identify vulnerable patients are sought. This may have important clinical implications because such patients could receive more aggressive antiarrhythmic therapy or may undergo prophylactic ablation of arrhythmia substrate to prevent the occurrence of arrhythmias and ICD discharges. Indeed, some studies suggested that it might be worth to perform prophylactic ablation of VT in patients with previously implanted ICD, however, this approach has not entered into daily clinical practice.

One of the methods of risk stratification for sudden cardiac death which has been used for many years, is programmed ventricular stimulation (PVS). This is an invasive study assessing the likelihood of VT or VF induced by stimulation to occur. This test has been also used in order to qualify for prophylactic ICD implantation in patients with LVEF 31-40% and non-sustained VT in ambulatory ECG. The primary disadvantage of PVS is its invasiveness. Modern ICDs are relatively complex devices with a number of functions, including the possibility to perform NIPS with implanted electrode located in the right ventricle. NIPS is readily available, inexpensive, minimally burdening ICD battery and less disturbing to the patient, because it does not require any invasive procedure.

Some studies suggested that appropriate interventions occur more frequently in patients who had ventricular arrhythmias induced by NIPS, but prognostic significance of NIPS has not yet been determined. One of the first NIPS-related studies demonstrated that VF/VT inducibility during the test of the device can help to optimize ICD programming, however, predictive value of NIPS had not been studied at that time. In another study, one of the first and few on the prognostic value of NIPS, it has been shown that induction of monomorphic, especially relatively slow VT (cycle length> 280ms) was prognostic for recurrence of arrhythmias. This study was relatively small, the distribution of etiology had not been considered, and some of the results were surprising, eg. previous myocardial infarction of inferior wall, rather than the anterior wall, predicted altered outcome, while LVEF had no prognostic value. In addition, these studies had been carried out many years ago, when the use of primary angioplasty for acute myocardial infarction was low, and therefore the clinical characteristics of the patient groups from that period are different than those of contemporary patients.