Current role and future perspectives for radiofrequency catheter ablation of postmyocardial infarction ventricular tachycardia

PULSED-FIELD ABLATION: COMPUTATIONAL MODELLING OF ELECTRIC FIELDS FOR LESION DEPTH ANALYSIS

Background

Pulsed-field ablation (PFA) is an emerging and promising nonthermal technology for cardiac ablation. The effective applied voltage to achieve adequate irreversible myocardial injury is not well studied. The pulsed-field strength remains independent of tissue contact; therefore, PFA is assumed to be an ablation technology, not mandating the need for tissue contact.

Objective

Determine the effect of applied voltage and distance to surface on depth of myocardial injury using PFA.

Methods

A computational model was developed and validated based on extracted data from in vivo studies to examine the effect of different applied voltages and the impact of distance between the catheter and endocardial surface on the depth of irreversible myocardial injury using PFA.

Results

The depth of lesions created by PFA are dose-dependent, and there is a direct correlation between applied PFA voltages and depth of irreversible myocardial injury. The minimum applied voltage of PFA required to create a lesion deeper than 1 mm is 300 volts. The catheter-tissue contact plays a pivotal role in determining lesion depth. With optimal catheter contact in the absence of trabeculation, the minimal applied energy required to achieve a 3-mm-deep lesion is 700 volts. A minor increase in the catheter-tissue distance of 1–2 mm doubles the minimum required applied voltage, increasing it to 1500 volts.

Conclusion

PFA is an important new technology that is proposed to be more efficacious and safer than currently used thermal ablation. Here we demonstrate the impact of dose dependence and the need for maintaining tissue contact during ablation.

Atrial Unipolar Potential in Radiofrequency Catheter Ablation of Atrial Tachycardia

We conducted this study to verify the efficacy of atrial unipolar potentialfor for ablation of atrial tachycardia. The morphology of atrial unipolar potential at the successful and the best unsuccessful ablation sites was analyzed in 35 patients with atrial tachycardia (sino-atrial reentrant tachycardia (SART) 15, adenosine-sensitive atrial reentrant tachycardia near the His bundle (HAT) 10, and non-reentrant ectopic atrial tachycardia (EAT) 10). The usefulness of atrial unipolar potential was compared with the Ao-Po interval. The incidences of QS pattern at the successful and the best unsuccessful sites were (successful versus unsuccessful; P, respectively) 93 versus 55%; P = 0.20 in SART, 90 versus 0%; P = 0.0001 in HAT, and 90 versus 10%; P = 0.001 in EAT. The mean Ao-Po intervals at the successful and the best unsuccessful sites were 35 versus 30 ms; NS in SART, 48 versus 45 ms; NS in HAT, and 58 versus 50 ms; NS in EAT. A significantly higher incidence of transient success at QS pattern sites was observed in SART than in HAT or EAT (n = 2 +/- 0.8 versus 0.2 +/- 0.1 and 0.1 +/- 0.1, P = 0.0005), and each transient site and final success site in SART was distributed linearly. The sensitivity and specificity of QS patterns with regard to the determination of appropriate target sites were 0.91 and 0.45 in SART, 0.9 and 1.0 in HAT, and 0.88 and 0.88 in EAT, respectively. In ablation of HAT and EAT, the QS pattern is very useful and should be given high priority when determining the optimum target site. In SART, the ablation success was often achieved by multiple, linear RF delivery near perinodal tissue, and the QS pattern could be a candidate for the optimum target site.

Ventricular Unipolar Potential in Radiofrequency Catheter Ablation of Idiopathic Non-Reentrant Ventricular Outflow Tachycardia

We conducted this study to verify the efficacy of ventricular unipolar potential (V-uni) for ablation of idiopathic non-reentrant ventricular tachycardia (idio-VT). The morphology of V-uni at the successful and unsuccessful sites was analyzed in 27 patients with idio-VT [20 with right ventricular outflow tachycardia (RVOVT) and 7 with left ventricular outflow tachycardia (LVOVT)]. The usefulness of V-uni was compared with a pacemapping method and the V-QRS interval. The incidence of QS-pattern V-uni at the successful and best unsuccessful sites were 100 versus 25% (P = 0.000005) in RVOVT and 86 versus 29% (P = 0.10) in LVOVT. The pacemapping scores at the successful and best unsuccessful sites were 11.5/12 versus 11.2/12; NS in RVOVT, and 11.2/12 versus 11.1/12; NS in LVOVT. The mean V-QRS interval at the successful and the best unsuccessful sites were 22.5 +/- 3.8 versus 21.6 +/- 3.4 msec; NS in RVOVT, 15.1 +/- 3.2 versus 12.5 +/- 3.3 msec; NS in LVOVT. The sensitivity (sen) and specificity (spe) of QS-pattern V-uni to determine the optimum target sites were 1.0 and 0.89 in RVOVT and 0.86 and 0.83 in LVOVT, respectively. In the ablation of idio-VT, QS-pattern V-uni is simply and visually identifiable, is very useful, and should be given a high priority when determining the optimum target site.

Therapeutic decision tree for patients with sustained ventricular tachyarrhythmias or aborted cardiac arrest: a critical review of the Antiarrhythmics Versus Implantable Defibrillator trial and the Canadian Implantable Defibrillator Study

Antiarrhythmic drugs, mainly amiodarone and sotalol, radiofrequency catheter ablation, and the implantable cardioverter defibrillator (ICD) are the 3 therapeutic options in patients with sustained ventricular tachycardia (VT) or ventricular fibrillation (VF). Idiopathic VT, incessant VT, frequently recurring, hemodynamically stable VT, and VT based on bundle branch reentry, are candidates for radiofrequency catheter ablation. Patients with high-risk ventricular tachyarrhythmias should receive ICDs as initial therapy. Two studies, the Antiarrhythmics Versus Implantable Defibrillator trial (AVID) and the Canadian Implantable Defibrillator Study (CIDS) have tried to approach the problem of these high-risk ventricular tachyarrhythmias. Although at 3 years, the ICD in AVID demonstrated a significant relative risk reduction over amiodarone of 31.5%, CIDS could not duplicate this finding. At 3 years, the relative risk reduction conferred by the ICD over amiodarone in CIDS was only 13.7%. A careful analysis of both studies suggests that CIDS was insufficiently powered to demonstrate statistically significant benefits similar to those shown by AVID, and furthermore, seemed to include an undetermined number of low-risk VT patients. The problem in the CIDS trial in this regard was the recruitment of patients in whom the inclusion criteria were met by the arrhythmias induced during the electrophysiology stimulation study, but which did not exist in real life. In addition CIDS included 14% of patients with (1) undocumented syncope and inducible monomorphic sustained VT; or (2) long runs of spontaneous nonsustained VT. Under these circumstances, the therapeutic implications of AVID remain unchallenged.

Management of postinfarct ventricular tachycardias

The clinical profile of patients with postinfarct VT has changed in the past two decades. Along with these changes, existing treatments have improved, and entirely new therapeutic approaches have been developed. The expanded range of treatment options has made postinfarct VT a less imposing clinical problem than it once was. Emerging therapies promise to make an even greater beneficial impact. The challenge in treating patients with postinfarct VT has changed from merely keeping patients alive to keeping up with innovations in therapy that can provide them with a better quantity and quality of life.

Radiofrequency catheter ablation of frequent monomorphic ventricular ectopic activity

INTRODUCTION

Frequent ventricular ectopic beats can result in severe symptoms and may even be incapacitating in some patients. Although radiofrequency catheter ablation is an effective and safe therapy for drug refractory idiopathic ventricular tachycardia, it has not been widely used in ventricular ectopy. The purpose of this study was: (1) to assess the potential role of catheter ablation in eliminating monomorphic ventricular ectopy in symptomatic patients regarding feasibility and safety and (2) to determine the usefulness of various mapping strategies.

METHODS AND RESULTS

Forty-one patients with symptomatic ventricular ectopic activity (right ventricular origin in 23 patients, left ventricular origin in 18 patients) were enrolled. The mean frequency of ventricular ectopic beats was 1512+/-583/hour documented by Holter ECG monitoring. These patients had previously been unable to tolerate or had been unsuccessfully treated with a mean of 3+/-1 antiarrhythmic agents. The site of origin was mapped using earliest endocardial activation times, unipolar electrograms and pace mapping. Radiofrequency ablation was successful in 34 (83 %) of 41 patients. Multivariate logistic regression analysis revealed pace mapping as the only independent predictor for a successful ablation site (P < 0.01). After a follow-up of 3 months, the overall success rate was 71%. The mean frequency of ventricular ectopic beats after successful ablation was 12+/-10 ventricular premature beat/hour.

CONCLUSION

Radiofrequency catheter ablation is an effective and safe treatment for frequent symptomatic drug refractory monomorphic ventricular ectopic activity. Pace mapping predicts best successful ablation of ventricular ectopic beats.

Therapeutic options for malignant ventricular tachyarrhythmias: is the implantable cardioverter-defibrillator a primary alternative or merely complementary?

In considering alternatives to the implantable cardioverter-defibrillator (ICD) in patients with malignant ventricular arrhythmias, both pharmacologic and nonpharmacologic therapies are available. Unfortunately, both pharmacologic methods (even when therapy is individualized and optimized) and nonpharmacologic methods (including coronary revascularization and radiofrequency or surgical ablation) yield long-term results that are unacceptable for many patients. Thus, the ICD should be strongly considered as complementary therapy, even when alternative methods are selected. More importantly, early implantation of an ICD often may be justified as the first therapeutic alternative, rather than as complementary therapy, in patients with life-threatening ventricular arrhythmias.