Ventricular tachycardias (VT) include a spectrum of arrhythmias that range from non-sustained asymptomatic VT to sustained arrhythmias, which can produce hemodynamic disturbances and cardiac arrest. These arrhythmias can be caused by a variety of disorders such as: chronic ischemic heart disease, cardiomyopathy, congenital and valvular heart disease, drug toxicity, metabolic disorders, long QT
syndromes, or even in the structure of normal hearts. Programmed electrical stimulation is the tool of dynamic electrophysiology testing. It has been used in documented or suspected VT to: 1. Confirm the diagnosis of VT. 2. Define the mechanism of arrhythmia. 3. Localize the site of origin of VT. 4. Evaluate the efficacy of pharmacologic and non pharmacologic therapeutic methods. Various protocols of programmed electrical stimulation have been used to induce ventricular arrhythmias in different laboratories. These protocols differ from each other in: number of extrastimuli used, paced cycle length, sites of stimulation and the current used (voltage and pulse width). Most of these protocols are time consuming. The purpose of the present study was to evaluate a proposed protocol for ventricular arrhythmia induction by comparing it to a standardized protocol. The second goal was to assess the predictive power of the following non-invasive
parameters on ventricular arrhythmia inducibility: QT dispersion (QTd), QRS dispersion (QRSd), heart rate variability (HRV), heart rate turbulence (HRT), left ventricular ejection fraction (LVEF), cardiac axis. The patient group included Group I: 25 patients admitted for ventricular arrhythmia induction during
electrophysiology (EP) study in whom the proposed protocol of ventricular arrhythmia induction was applied.
Group II: 20 patients admitted for ventricular arrhythmia induction during electrophysiology (EP) study in whom a standardized protocol of ventricular arrhythmia induction was applied. The proposed protocol of ventricular arrhythmia induction consisted of 2 and 3 extrastimuli delivered at predetermined fixed coupling intervals during pacing at 400 and 600 ms drive cycle length both at right ventricular apex (RVA) and right ventricular outflow tract (RVOT). Burst pacing and Short-long-Short cycles were also used. When comparing the proposed protocol with the standardized protocol of programmed ventricular stimulation (PVS) there was no significant difference in ventricular arrhythmia inducibility between group I and Group II.
EF was significantly lower in the group of patients in whom ventricular arrhythmia was induced as compared to the non-induced group. QRSd and QRSd+QTd were significantly longer in the induced group. From the HRV parameters measured (SDNN, RMSSD, PNN50, and short-term HRV); only the short-term HRV was significantly lower in the induced group. Turbulence onset (TO) as a parameter of HRT was significantly different between the induced group as compared to the non-induced group. In conclusion, the modified protocol proposed in this study can be accepted as a protocol for PVS. Left ventricular EF, QRSd, QRSd+QTd, short-term HRV, TO parameters may be used to assess the patient predisposition for ventricular arrhythmias.