The usefulness of Holter monitoring in selecting pharmacologic therapy for patients with sustained monomorphic ventricular tachycardia: studies in patients in whom no effective pharmacologic therapy could be determined by electrophysiologic study

Role of electrophysiologic study (EPS)-guided preventive therapy for the management of ventricular tachyarrhythmias in patients with heart failure

BACKGROUND

Ventricular tachyarrhythmias (VT/VF) are 1 of the most important factors determining the prognosis of patients with heart failure (HF). Although priority is given to implantable cardioverter defibrillator (ICD) therapy for the prevention of sudden cardiac death, electrophysiologic-study (EPS)-guided preventive therapy could be important for reducing the number of cardiac events.

METHODS AND RESULTS

Of 864 patients with a history of HF, an EPS was performed in 168 and 121 had inducible VT/VF. Under the basic therapy of an ICD, additional catheter ablation was attempted for 95 of 124 monomorphic VT foci in 74 patients, and 78 of the VT were successfully ablated. The prognoses were compared among 5 patient groups with different results for the EPS and catheter ablation: (1) success group (n=43), (2) failure group (n=15), (3) not attempted group (n=16), (4) VF group (n=47), and (5) no inducible VT/VF group. During a follow-up period of 31+/-22 months, the incidence of VT/VF was lower in the success and no inducible VT/VF groups than in the other groups (p=0.0018), although a significant difference was not observed for the total deaths.

CONCLUSION

EPS-guided preventive therapy using an ICD and catheter ablation can be useful, at least for the reduction of arrhythmic events in patients with HF.

Clinical usefulness of electrophysiologic study (EPS)-guided risk stratification for life-threatening arrhythmia in patients with heart failure

BACKGROUND

Ventricular tachyarrhythmia is one of the most important factors determining the prognosis of patients with heart failure and sudden death can be observed even during stable therapy controlling clinical heart failure. In this study, the usefulness of electrophysiologic study (EPS) for the prediction of a future arrhythmic event was evaluated in patients with heart failure.

METHODS AND RESULTS

The patient population consisted of 474 patients with a history of clinical heart failure but without an episode of spontaneous sustained ventricular tachycardia or fibrillation (VT/VF). A Holter ECG was performed in all patients, and 177 of the 474 patients underwent EPS because of a recording of nonsustained VT (NSVT, > 5 beats). When sustained VT/VF was inducible in EPS, the patient was assigned to implantation of a defibrillation device. The patients were divided into 3 groups, ie, 1) no NSVT (n = 297), 2) NSVT + no inducible VT/VF (n = 134), and 3) NSVT + inducible VT/VF (n = 43), and were followed-up for > 12 months. All patients were followed-up under standard therapy for heart failure. There were no significant differences in basic clinical characteristics and therapies among the 3 groups. During the follow-up period of 32 +/- 18 months, 56/474 patients suffered a VT/VF episode, ie, 21/297 in no NSVT, 14/134 in NSVT + no inducible VT/VF, and 21/43 in NSVT + inducible VT/VF patients (P = 0.032). All patients were rescued from sudden death among patients with an implanted defibrillator, but 11 patients without a defibrillator died.

CONCLUSION

In patients with heart failure, future arrhythmic events could be predicted by EPS and Holter ECG. EPS-guided risk stratification seems to be useful in managing patients with heart failure.

Clinical significance of the electrophysiologic study (EPS)-guided therapy for the secondary prevention of ventricular tachycardia

BACKGROUND

Although electrophysiologic study (EPS) is one of the most reliable methods for selecting preventive therapy for patients with sustained ventricular tachycardia (VT), VT may recur during EPS-guided effective therapy; therefore, the importance of implantable cardioverter-defibrillator (ICD) has been emphasized. In this study, the prognoses of VT patients were evaluated to clarify the importance of EPS-guided therapy for the secondary prevention of VT.

METHODS AND RESULTS

The study population consisted of 99 consecutive patients with a history of sustained VT, which was inducible in EPS. The VT induction protocol used 1-3 extrastimuli and rapid ventricular pacing at 2 right ventricular sites and included additional isoproterenol infusion. ICD implantation was applied to all patients with an episode of hemodynamically unstable VT, regardless of the result of preventive therapy. For preventive therapy, an antiarrhythmic drug and/or catheter ablation were selected, and they were defined as being effective in the EPS-guided therapy when the induction of VT was completely prevented. When no therapy was effective for prevention, an antiarrhythmic drug was prescribed under ICD implantation. During the follow-up period of 19+/-20 months, VT recurred in 17 of 32 patients (53%) in the ineffective group and in 10 of 67 patients (15%) in the effective group (p=0.0001). The therapies used in the effective group were class I antiarrhythmic drug in 9, class III in 15, and catheter ablation in 35 patients. Between the patients with and without VT recurrence, there were no significant differences in the left ventricular ejection fraction and the maximum number of repetitive ventricular responses that remained in VT induction in EPS.

CONCLUSIONS

Although VT may recur in up to 15% of patients with EPS-guided effective therapy, the recurrence rate was significantly reduced in comparison to that in the ineffective group. EPS-guided therapy may be useful to reduce the clinical recurrence of VT, as well as the action of ICD.

Pediatric Cardiac Electrophysiology

The rapid development of invasive cardiac electrophysi ologic procedures, including the insertion of rate-responsive pacemakers, radiofrequency catheter ablation (RFA), and the implantation of cardiac defibrillators has given pediatric cardiac electrophysiologists better techniques to treat in fants and children with arrhythmias. Expertise on the basic pathophysiologic mechanisms of arrhythmias is a requisite in performing invasive intracardiac electrophysiologic pro cedures. Techniques for invasive cardiac electrophysiologic procedures (EPS) in pediatric patients are similar to those for diagnostic cardiac catheterization. The choice of anes thesia is determined by institutional preference, patient's age, anticipated sites of intravascular access, and type of procedure. The goal is to avoid agents that depress myocar dial contractility or affect cardiac conduction or refractori ness. EPS equipment includes multielectrode catheters, a multichannel recording system, an electrical stimulator, and a fluoroscopy unit. EPS require the ability to induce, termi nate, and modify cardiac arrhythmias. The objectives of the EPS include definition of the mechanisms of observed and induced cardiac arrhythmias, determination of risk for sudden cardiac arrhythmic death, investigation of antiar rhythmic drug efficacy, and ablation of tachyarrhythmia sub strates. This is accomplished by evaluating electrophysi ologic properties, such as automaticity, conduction, and refractoriness; by initiating and terminating tachycardias; by mapping sequence of activation; and by evaluating patients for various forms of therapy and judging the response to therapy. Though generally quite low, the associated morbid ity and mortality in performing EP study and RFA in pediatric patients varies considerably, depending on the patient's age and size, diagnosis, associated cardiac defects, and prepro cedure condition.

Leakage of energy to the body surface during defibrillation shock by an implantable cardioverter-defibrillator (ICD) system--experimental evaluation during defibrillation shocks through the right ventricular lead and the subcutaneous active-can in canines

The leakage of electrical current to the body surface during defibrillation shock delivery by an implantable cardioverter-defibrillator (ICD) device (the Medtronic Jewel Plus PCD system) was evaluated in 5 dogs. The defibrillation shocks were delivered between the active-can implanted in the left subclavicular region and the endocardial lead placed in the right ventricle at the energy levels of 1, 2, 8, 12, 24 and 34 J. During each delivery, the electrical current leakage from the body surface was measured by electrodes connected to a circuit at 4 recording positions: (A) parallel-subcutaneous (the electrodes were fixed in the subcutaneous tissue of the left shoulder and the right lower chest, and the direction of the electrode vector was parallel to the direction of the defibrillation energy flow); (B) cross-subcutaneous (the electrodes were fixed in the subcutaneous tissue of the right shoulder and the left lower chest, and the vector of the electrodes was roughly perpendicular to the direction of the energy flow); (C) parallel-surface (the electrodes were fixed with ECG paste on the shaved skin surface at the left shoulder and the right lower chest); and (D) surface grounded (the electrodes were fixed on the shaved skin surface at the left shoulder and the left foot, which was grounded). The circuit resistance was set at a variable level (100-5,000 ohms) in accordance with the resistance measured through each canine body. Leakage energies were measured in 750 defibrillation shocks with each circuit resistance in 5 dogs. The leakage energy increased in accordance with the increase of the delivered energy and the decrease of the circuit resistance in all 4 recording positions. When the circuit resistance was set at 1,000 ohms, the leakage energy during shock delivery at 34 J was 32+/-17 mJ at position A, 5+/-9 mJ at B, 10+/-9 mJ at C, and 4+/-3 mJ at D (p=0.042). The peak current was highest at position A and was 87+/-22 mA with a circuit resistance of 1,000 ohms. The power of the leakage energy depended on the delivered energy and the impedance between the electrodes. The angle between the alignment of the recording electrodes and the direction of the energy flow was another important factor in determining the leakage energy. Although the peak current of the leakage energy reached the level of macro shock, the highest leakage energy from the body surface was considerably less because of the short duration of the shock delivery.

Electrophysiologic parameters to predict clinical recurrence of ventricular tachycardia in patients under electrophysiologic study-guided effective pharmacological therapy

Although an electrophysiologic study (EPS) is the most reliable method for selecting the treatment for a patient with sustained ventricular tachycardia (VT), VT recurrence may occur even during EPS-guided effective therapy. Electrophysiologic parameters were compared between patients with and without arrhythmic events under EPS-guided effective therapy to identify the predictive parameters of VT recurrence during the clinical course. The study population consisted of 77 consecutive patients with sustained VT who were receiving long-term pharmacological therapy that was demonstrated to be effective by the EPS assessment. The VT induction protocol employed 1-3 extrastimuli and rapid ventricular pacing at 2 right ventricular sites and 1 left ventricular site, and isoproterenol was infused when VT was not induced. To determine the 'effective' antiarrhythmic drug, all sustained ventricular arrhythmias had to be prevented during the whole induction protocol, but repetitive ventricular responses (RVR) were allowed to remain for up to 5 beats when they were in the same QRS configurations as the clinical VT and up to 12 beats when they were in polymorphic QRS configurations. The effective refractory periods (ERPs) at the 3 ventricular pacing sites and their difference (i.e., ERP-dispersion) and the maximum number of RVR beats were evaluated in an EPS during the control state and at the time of drug assessment. In the comparison of patients with and without VT recurrence, there was no significant difference in clinical characteristics or ERPs, but the deltaERP-dispersion (i.e., the increase in ERP-dispersion caused by the antiarrhythmic drug) and the maximum number of RVRs were significantly smaller in the group of patients without VT recurrence (deltaERP-dis, -3+/-8 vs. 6+/-12, p = 0.0027; maxRVR, 3+/-3 vs. 5+/-4, p = 0.0160). The VT recurrence rate was significantly lower in the patients with deltaERP-dis < or =0 or maxRVR<6 in comparison with the others (p = 0.01 14 and p = 0.0360). Patients with VT recurrence showed greater deltaERP-disp and a longer duration of RVRs at the time of drug assessment in comparison with the patients without VT recurrence. The prognosis of patients under EPS-guided therapy may be improved by the use of stricter criteria for drug assessment in the EPS, although this may decrease the number of drug responders determined in the EPS.