Journal of Interventional Cardiac Electrophysiology

, Volume 25, Issue 3, pp 229–234

Ventricular tachycardia inducibility after radiofrequency ablation affects the outcomes in patients with coronary artery disease and implantable cardioverter-defibrillators: The role of left ventricular function

Authors

    • Department Heart and VesselsUniversity of Florence
    • Laboratorio di ElettrofisiologiaAzienda Ospedaliero-Universitaria di Careggi
  • Marzia Giaccardi
    • Department Cardiovascular RehabilitationDon Gnocchi Foundation
  • Raffaele Molino Lova
    • Department Cardiovascular RehabilitationDon Gnocchi Foundation
  • Carmine Liccardi
    • Department Heart and VesselsUniversity of Florence
  • Gian Franco Gensini
    • Department Heart and VesselsUniversity of Florence
    • Department Cardiovascular RehabilitationDon Gnocchi Foundation
Article

DOI: 10.1007/s10840-008-9351-x

Cite this article as:
Colella, A., Giaccardi, M., Lova, R.M. et al. J Interv Card Electrophysiol (2009) 25: 229. doi:10.1007/s10840-008-9351-x
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Abstract

Purpose

We hypothesized that inducibility of the VT responsible for ICD therapies at the end of RFCA, would also be associated with a differential risk, depending on left ventricular function.

Methods

We retrospectively studied 66 patients with previous myocardial infarction and with ICD who also underwent RFCA for recurrent refractory VTs.

Results

During the follow-up only 19 patients (29%) showed VTs. Among patients with ejection fraction (EF) ≤ 35%, 11 out of 25 still continued to have VT recurrences, independent of the inducibility of the VT. Among patients with EF >35% and <50%, no recurrent VT was any longer detected in the nine patients in whom the VT was not inducible, while VT recurrences still continued only in the eight patients in whom it was. Finally, all the 24 patients with EF ≥50% did not show any recurrent VT.

Conclusions

Our findings confirm the role of RFCA in reducing ICD therapies and also place RFCA in the overall clinical management of recurrent post infarction VTs according to the left ventricular function.

Keywords

Sudden deathVentricular tachycardiaImplantable defibrillatorsCatheter ablationEjection fraction

1 Introduction

Cardiac arrest due to acute ventricular tachycardia (VT) is the most common cause of sudden death in the developed countries [1, 2]. A large body of evidence has shown that approximately 75% of victims suffer from coronary artery disease and that a previous myocardial infarction is the condition responsible for the cardiac arrest [3]. Several prospective trials have also demonstrated a survival benefit from implantable cardioverter-defibrillators (ICDs) and a neutral or harmful effect of chronically administered antiarrhythmic drugs [1, 2, 4, 5]. However, in spite of being life saving devices, ICDs bring out several drawbacks to the recipients [6] and impact adversely on their quality of life [1, 7, 8]. In fact, ICD shocks are painful, repeated ICD shocks within a short time interval (ICD “storms”) occur in 10–25% of cases [9, 10] and patients may experience syncope before ICD therapy is delivered. Clinically relevant anxiety and depression, as a result of recurrent ICD shocks, occur in more than 50% of patients [6, 11, 12]. Further, it has been observed that patients receiving ICD shocks show an increased rate of congestive heart failure and mortality [13, 14]. Finally, ICD do not provide an absolute protection against death due to arrhythmias, being the rate of sudden death among patients with ICD approximately 5% [15].

On the other hand, the role of radiofrequency catheter ablation (RFCA), also proposed as an alternative non-pharmacological treatment for VT [16, 17, 18], is still under debate. One previous trial [19] has, in fact, shown that RFCA is poorly effective in the prevention of VT recurrences in those patients with structural heart disease, while a more recent trial [20] has shown that RFCA is able to reduce the risk of receiving ICD therapy, either shocks or anti-tachycardia pacing, in patients with a history of myocardial infarction. However, in both the above trials, no further indication is provided on predictors of VT recurrences among those patients who also received RFCA. Indeed, the identification of such predictors might better clarify the role of RFCA in the overall clinical management of recurrent post infarction VT. In fact, though previous studies [21] have shown that poor left ventricular function is a strong independent predictor of recurrent VTs, information on predictors of VT recurrences in patients with moderately depressed or normal left ventricular function is still scant.

In this study we hypothesized that whether the VT responsible for ICD shocks (clinical VT) was still inducible at the end of the RFCA procedure, this would be associated with a differential risk of VT recurrences, depending on left ventricular function. Accordingly, we retrospectively tested this hypothesis in a sample of patients with previous myocardial infarction and with ICD who also underwent RFCA for recurrent refractory VTs.

2 Methods

We studied 66 consecutive patients (48 men and 18 women, mean age 62.6 ± 6.6 years) referred to our department for RFCA of recurrent VT. All patients, suffering from CAD and with a history of previous myocardial infarction, had previously received an ICD implant for primary or secondary prevention of sudden cardiac death and had been re-vascularized as completely as possible at the time of the implant. Despite optimal drug therapy, all patients had at least two sustained VTs or one sustained plus one non-sustained VT responsible for ICD therapies and documented by the electrograms stored in the ICD in the previous 3 months. All patients gave their written informed consent to undergo the RFCA.

On admission patients underwent a complete clinical and instrumental evaluation, including cardiac Echography, and RFCA procedure was performed within 2 days from admission.

All procedures were performed with the patients in sinus rhythm. Two quadripolar electrode catheters (Bard Inc. Salt Lake City, UT, USA) were inserted into a femoral vein and positioned in the apex of the right ventricle, for the programmed ventricular stimulation, and in the coronary sinus, for the correct sensing of ventricular signal. The inducibility of the VTs was assessed by programmed ventricular stimulation with up to three extrastimuli, using basic drive cycle lengths of 600, 400, and 350 ms. Catheter access to the left ventricle was achieved via the retrograde aortic approach in 64 patients and via the trans-septal approach in two patients, due to the presence of aortic prosthetic valves. During both left ventricular mapping and ablation, heparin was administered in order to achieve and maintain an activated clotting time between 250 s and 300 s.

The left ventricular electroanatomic mapping was performed using the CARTO system [22]. Endocardial electrograms were recorded using a deflectable 7 Fr (NaviStar ThermoCool, BioSense-Webster Inc. Diamond Bar, CA, USA.) with a 4-mm-tip distal electrode and bipolar maps were obtained. A voltage >1.5 mV identified normal tissue, a voltage <1.5 mV abnormal tissue and a voltage <0.5 mV densely scarred tissue; further, endocardial surface areas were calculated assuming multiple rectangular or trapezoidal shapes of either abnormal or densely scarred tissues [17]. Pace-mapping was performed during sinus rhythm in the border zone between the scar and normal tissue to approximate the exit site of each inducible VT. Once detected, a delay in stimulus to QRS interval during pace-mapping within the scar was used to identify putative proximal sites of the VT circuit. Sequential point lesions were linearly extended from the areas showing the lowest amplitude signal (<0.5 mV) to areas showing a distinctly normal signal (>1.5 mV). For each point lesion, radiofrequency energy was applied for 60 s using a power output able to achieve a targeted temperature of 50°C, with continuous monitoring of impedance. Programmed ventricular stimulation was repeated after the end of RFCA to assess the inducibility of specific, targeted tachycardia morphologies. RFCA procedures were defined as successful when the VT responsible for the ICD therapies was terminated by an application of radiofrequency energy and was no longer inducible by programmed ventricular stimulation.

After the procedure patients reassumed the same antiarrhythmic drugs as before the RFCA. Patients were monitored during their stay in hospital and followed as outpatients 1 week and then every 3 months after discharge. The diagnosis of recurrent VT was based upon the record of delivered ICD therapies. Further, when interrogation of the ICD allowed a precise determination of the cycle length of the VT responsible for ICD therapies, this last was considered consistent with the ablated VT if its cycle length was included within ±20 ms of the ablated VT. When interrogation of the ICD did not provide reliable information on the cycle length of the VT responsible for ICD therapies, this last was however considered consistent with the ablated VT.

Statistical analysis was performed using the STATA 7.0 software, from Stata Corporation (College Station, TX, USA). Continuous variables are reported as means, along with their standard deviations, and categorical variables are reported as percentages. Continuous variables were compared using the two-tailed Student “t” test for either paired or independent samples, as appropriate. Categorical variables were compared using the two-tailed Pearson’s χ2 test. Multivariate analysis was performed using a logistic regression based model. Type 1 error was set at 0.05.

3 Results

No relevant adverse event occurred during either the procedure or the follow-up. The mean follow-up was 26.2 ± 12.2 months after RFCA. Only 19 patients (29%) continued to show clinical VTs, while 47 (71%) did not show any recurrent VT during the follow-up. Among the 19 patients (eleven with EF ≤ 35% and eight with EF>35% and <50%) who showed recurrent clinical VTs, ICD therapies, either shocks or anti-tachycardia pacing, dropped from 6.4 ± 3.3, in the 3 months before the RFCA procedure, to 2.5 ± 2.0, in the subsequent 3 months (p < 0.001). After the procedure, patients were followed every three months and at the last three-month follow-up available for each patient ICD therapies, that included both shocks and antitachycardia pacing, did not show any significant difference when compared with the first three-month follow-up (2.4 ± 1.8).

Table 1 shows patients’ characteristics according to the presence vs. absence of recurrent VT. No significant difference was found with regard to age, gender, time from the myocardial infarction, use of drugs, ICD documented events in the 3 months before RFCA and duration of the follow-up. On the contrary, left ventricular ejection fraction (EF) was significantly lower in those showing recurrent VTs. Further, in 14 out of the 19 patients who showed recurrent VTs during the follow-up, the clinical VT was inducible at the end of the RFCA procedure. The multiple logistic regression based model, with VT recurrence as the dependent variable, used to assess possible interactions between poor left ventricular function and VT inducibility at the end of the procedure, showed that both EF (OR 0.91, 95%CI 0.84–0.98, p = 0.016) and VT inducibility (OR 16.3, 95%CI 3.1–86.2, p = 0.001) were independent predictors of VT recurrences. Further, based upon EF tertiles, we divided our patients in poor (≤ 35%), moderately depressed (>35% and <50%) and preserved (≥50%) left ventricular function. Among patients with EF ≤ 35%, 11 out of 25 (44%) still continued to have VT recurrences, independent of whether the VT responsible for ICD therapies was inducible (six patients) at the end of the procedure or not (five patients). Among patients with EF >35% and <50%, no recurrent VT was any longer detected in the nine patients in whom the clinical VT responsible for ICD therapies was not inducible at the end of the procedure (100% specificity), while VT recurrences still continued only in the eight patients in whom the clinical VT was inducible (100% sensibility). Finally, in all the 24 patients with EF ≥50% no recurrent VT was any longer detected during the follow-up.
Table 1

Patients’ characteristics according to the presence vs. absence of recurrent VTs after RFCA (n. 66)

 

Recurrent VTs

No recurrent VTs

 

(n. 19)

(n. 47)

p (*)

Clinical features

- Age (years) (mean ± SD)

62.6 ± 6.6

62.5 ± 6.7

0.951

- Sex (% women)

32

28

0.617

- Time from AMI (months) (mean ± SD)

13.9 ± 3.9

13.0 ± 3.6

0.407

- Ejection fraction (%) (mean ± SD)

34.5 ± 8.9

44.7 ± 11.8

<0.001

Use of Drugs

- Propafenone (%)

13

13

0.968

- Lidocaine (%)

53

45

0.608

- Beta-blockers (%)

67

68

0.942

- Calcium-channels-blockers (%)

7

10

0.734

- Amiodarone (%)

87

84

0.805

- ACE Inhibitors (%)

67

65

0.886

ICD documented events in the 3 months before RFCA

- SVT (n) (mean ± SD)

3.9 ± 1.9

4.4 ± 3.2

0.593

- NSVT (n) (mean ± SD)

7.8 ± 6.2

7.5 ± 6.5

0.863

- ATP (n) (mean ± SD)

2.1 ± 1.8

2.1 ± 2.5

0.967

- Total shocks (n) (mean ± SD)

3.8 ± 2.5

3.6 ± 2.3

0.804

- Inappropriate shocks (n) (mean ± SD)

1.1 ± 0.8

1.2 ± 0.8

0.814

Induced VTs at the end of the procedure (n)

14/19

5/47

<0.001

Follow-up (months) (mean ± SD)

32.0 ± 13.3

28.1 ± 13.0

0.349

(*) From two-tailed Student “t” test for independent samples or Pearson’s χ2 test, as appropriate.

4 Discussion

Previous studies have demonstrated both feasibility and efficacy of RFCA in reducing VT recurrences in patients with a history of myocardial infarction and with ICD [20, 2325], and our results also confirmed the efficacy of RFCA in reducing ICD therapies in these patients. Among the 66 patients referred to our clinic for RFCA of recurrent post infarction VTs, only 19 (29%) showed recurrences during the follow-up. This finding “per se” highlights the role of RFCA in the overall clinical management of recurrent post infarction VTs in patients with ICD. In fact, the only drug known to provide a significant reduction of ICD therapies is amiodarone, whose long term side effects are such that it can not be considered as a feasible therapeutic alternative [2628]. Poor left ventricular function has been shown to be the most powerful independent predictor of cardiac arrest in patients with either ischemic or non-ischemic cardiomyopathy [29] and when associated with VTs induced by the programmed ventricular stimulation at the end of the RFCA procedure it has also been shown to be predictive of death from heart failure [17, 30]. Our findings also confirmed the role of poor left ventricular function as an independent predictor of recurrent VT. Among patients with EF ≤35%, 11 out of 25 (44%) still continued to have VT recurrences, independent of whether the VT responsible for ICD therapies was inducible (six patients) at the end of the procedure or not (five patients). Most clinical trials [14, 3133] testing the efficacy of antiarrhythmic versus ICD therapy have used the EF as the marker for advanced disease, with the qualifying criteria in the range of 30–40% or less. Interestingly, in the AVID trial [34] a subgroup analysis suggested that there was no benefit of ICD therapy over amiodarone for patients with EF between 36% and 40%, being all the benefit accrued to those patients with EF 35% or less. This observation raises the critical question we addressed in conceiving this study about predictors of VT recurrences, and consequently about therapeutic options, for patients with EF greater than 35%. Our findings show that among patients with EF >35% and <50%, no recurrent VT was any longer detected in the nine patients in whom the VT responsible for ICD therapies was not inducible at the end of the procedure (100% specificity), while VT recurrences still continued only in the eight patients in whom the clinical VT was inducible (100% sensitivity). Actually, inducibility of the clinical VT, more than being a predictor of VT recurrences, is simply the consequence of RFCA failure [30], i.e. of the fact that the clinical VT has not been successfully ablated. Accordingly, at least in patients with EF >35% and <50%, the procedure should be repeated until an acutely successful ablation of the clinical VT is achieved. For these patients, in fact, RFCA might be considered a reasonable alternative to ICD as the first choice. Finally, our findings show that in all the 24 patients with EF >50% no recurrent VT was any longer detected during the follow-up.

Based upon our findings, a simple algorithm (Fig. 1) might be proposed for the management of recurrent VTs in patients with previous myocardial infarction:
  1. a)

    for patients with EF ≤35%, ICD still remains the first choice (class 1A). However, RFCA is indicated to reduce ICD shocks (class 1C) [1];

     
  2. b)

    for patients with EF >35% and <50%, the first choice might be RFCA and any effort should be made to successfully ablate the VT, possibly by repeating the procedure. The implantation of ICD might be limited to those patients in whom the VT is not successfully ablated.

     
  3. c)

    for patients with EF ≥50%, the first choice might be RFCA.

     
https://static-content.springer.com/image/art%3A10.1007%2Fs10840-008-9351-x/MediaObjects/10840_2008_9351_Fig1_HTML.gif
Fig. 1

Algorithm for the management of recurrent ventricular tachycardias in patients with myocardial infarction

However, a few considerations suggest that the above algorithm for the management of recurrent VTs in patients with previous myocardial infarction, should be regarded with caution. First, coronary artery disease is an active evolving disease, and the status of risk factors should be periodically monitored, in order to identify disease progression, with evolution from low to high risk status [3]. Second, this study was based upon a retrospective analysis and our findings need, by definition, to be confirmed by prospective studies. Third, despite the high degree of specificity and sensibility (100% for both) of the inducibility of the VT at the end of the procedure in predicting VT recurrences among patients with EF >35% and <50%, the sample we analyzed was, in effect, quite small.

5 Conclusions

Our findings confirm the relevant role of RFCA in reducing ICD therapy drawbacks and also place RFCA in the overall clinical management of recurrent post infarction VT according to the left ventricular function. Future studies are, however, strongly recommended to evaluate on a broader scale the role of RFCA in recurrent post infarction VTs, by implementing prospective randomized trials.

Copyright information

© Springer Science+Business Media, LLC 2008