Safety in Ventricular Tachycardia Ablation

Dr Michael Chi Yuan Nam
Specialist Registrar Cardiology
Southampton University Hospital NHS Trust

Currently only Implantable Cardiac Defibrillators (ICD) have consistently shown prognostic benefit in the treatment of malignant ventricular arrhythmia. However poorly controlled ventricular arrhythmia can result in decompensated cardiac function in addition to recurrent ICD discharge which causes significant morbidity. Ablation of ventricular tachycardia (VT) was first reported in the 1980’s and has progressed to a universally accepted treatment strategy for ventricular arrhythmia [1]. However the complexity of cases varies significantly depending on factors such as aetiology, comorbidity, and presentation. The introduction of novel techniques such as irrigated ablation catheters and pre-procedural MR/CT also explains variations in complication rates. Experienced centres have published important procedural data and this article forms a review of the current safety data available.

The 3 main procedural complications associated with VT ablation are vascular injury, thromboembolism, and cardiac tamponade.

Significant vascular complications occur in approximately 2% of VT ablations [2]. Central venous access techniques are used for right heart ablations or trans-septal puncture. Venous injury can result in venous thrombosis and embolism. The left ventricle can also be accessed via a retrograde transaortic approach, which carries arterial puncture complications of haematoma, AV fistula, and pseudoaneurysm formation.

Widespread practice of meticulous anticoagulation monitoring both before and during procedure in high-risk cases has resulted in low overall thromboembolic occurrence. Over 1000 ablations reported in 13 case series noted an overall 1.3% incidence of procedural-related cerebrovascular events [2].

Cardiac tamponade has a reported incidence of approximately 1% [2]. Radiofrequency ablation and irrigation catheter-associated ‘steam pops’ can cause mechanical perforation with the RV free wall at highest risk. Limiting radiofrequency power with open irrigation catheters are suggested to offer some protection.

The risks of the procedure are largely influenced by case setting; each of which will be discussed below.

Idiopathic VT
Structurally normal heart VT often carries a good prognosis. This group includes RV outflow tract VT, monomorphic extrasystoles, LV outflow tract VT, and fascicular VT. Ablation therapy is largely symptom driven. Idiopathic VT is also usually performed electively, which inevitably means a lower complication rate. Two large single center studies have observed an approximate 3% major complication rate; defined as those resulting in long-term disability, requiring intervention, or prolonging their inpatient stay [3, 4). Bohnen et al performed 119 idiopathic VT ablations over a 2-year period, with 2 cases of cardiac tamponade, 1 cerebrovascular event, and 1 pseudoaneurysm [4]. Another study by Peichl et al observed similar complication rates [3]. In both studies 30-day mortality was 0%.

Structural Heart Disease VT (SHD VT)
This group forms the bulk of the VT ablation patient population and includes prior MI, dilated cardiomyopathy, and ARVC/D. The 2009 EHRA Expert Consensus lists 5 recommendations for VT ablation [2];
1) Recurrent symptomatic sustained monomorphic VT (SMVT) refractory to antiarrhythmic therapy;
2) Incessant SMVT or VT storm without a reversible cause;
3) Frequent PVC, NSVT, or VT that causes ventricular dysfunction;
4) Bundle branch re-entrant or interfascicular VT;
5) Recurrent sustained polymopthic VT/VF refractory to antiarrhythmic therapy and where there is a suspected trigger amenable to ablation.

A metanalysis published in 2011 looking at 5 studies (457 cases) calculated a 35% absolute reduction in VT occurrence post ablation over a 6 month period [5, 6]. However the metanalysis also found no statistically significant difference in mortality.
 
Safety data is particularly variable in this setting due to the broad spectrum of disease severity, comorbidity, technical approach, and higher rates of electrical storm presentation.

Prophylactic VT ablation for patients eligible for ICD implantation has been addressed by 2 prospective clinical trials (SMASH-VT and VTACH; n=61 and n=46 respectively) [7,8]. In SMASH-VT they reported 3 ablation-related complications (4.9%); 1 pericardial effusion without tamponade managed conservatively, cardiac decompensation requiring prolonged hospitalisation, and a deep vein thrombosis requiring anticoagulation. The VTACH trial reported 2 procedural complications (3.7%) of TIA and transient ST elevation. There were no deaths within 30 days of the procedure in both trials.

Recent safety data addressing VT ablation for recurrent arrhythmia and their trials are summarised in the table below.

Study

Year

Centers

n

Age (median)

LVEF (%)

ICD (%)

Procedural Time (mins)

Stevenson

2008

18

231

68

25

94

229

Tanner

2009

8

63

66

28

42

257

Bohnen

2011

1

250

63

34

 

 

Peicl

2014

1

473

62

33

86

207

 

Complication Type*

Stevenson

n=231

Tanner

n=63

Bohnen

n=250

Peicl

n=473

Death

7 (3%)

0

1 (0.4%)

0

Perforation

1

3 (5%)

4 (1.4%)

3 (0.6%)

> Tamponade

1

0

4

2

>Haemopericardium

0

3

0

1

Thromboembolic Event

-

-

3 (1.2%)

4 (0.8%)

> Stroke/TIA

-

-

2

3

> DVT/PE

-

-

1

1

AV Block

-

-

-

5 (1%)

Vascular Access

-

-

5 (2%)

22 (4.7%)

> Retroperitoneal Bleed

-

-

1

-

> Pseudoaneurysm

4 (1.7%)

-

1

12

> Femoral AVF

-

-

1

3

> Groin Haematoma

-

1

3

7

> Bleeding

7 (3%)

-

-

-

Heart Failure

6 (2.6%)

-

1

-

Other

 

 

 

3 (0.6%)

> Device Lead dysfunction

1

1

-

1

> CPR intraprocedure

-

-

-

2

> Pericarditis

1

-

-

0

> COPD exacerbation

1

-

-

-

> Sepsis

1

-

-

-

> Haematuria

1

-

1

-

Total

31 (13%)

5 (8%)

15 (6%)

38 (8%)

* data not reported denoted by ‘-‘.

Major complication rates were very low despite most patients displaying poor cardiac reserve. A particular favourable outcome is a 0% procedural mortality after 473 cases reported by Peicl et al [3]. It is important to note that the studies differed in adverse event reporting. For example, sepsis and COPD exacerbation were considered procedural complications in Stevenson’s data only.

Conventional catheter ablation techniques applied to the left heart resulted in an observed 2.7% risk of cerebral or systemic embolism [9]. Many operators now use open irrigated ablation catheters which enable better surface cooling with consequent theoretical reduced thromboembolic risk by reducing coagulum formation on the catheter tip, and also improves ablation area and depth. However external irrigation can result in substantial saline infusion into the circulation which may have contributed to 7 cases of pulmonary oedema observed by Stevenson et al. In addition irrigated electrodes cause deep heating within tissue and subsequent steam formation can explode through tissue (‘steam pops’) causing perforation.

Perhaps surprisingly a meta-analysis of studies on VT ablation for ventricular arrhythmia storm (total 447 patients) found only a 2% complication rate [10]. Of these, procedure-related mortality was 0.6% (3 cases due to myocardial infarction, tamponade, and electromechanical dissociation), cerebrovascular events in 0.6%, heart block in 0.6%, and cardiac tamponade in 0.2%.

Epicardial VT ablation
Although irrigated ablation catheters improve depth of burn, some re-entry circuits lie deep in the subendocardium or in the epicardium. This is observed more frequently in ARVC and nonischaemic dilated cardiomyopathy. This has necessitated attempts of epicardial ablation via a percutaneous approach. One multicentre safety study reported the need for epicardial ablation in 13% of VT ablations (n=146) [11]. Pericardial access was successful in 90% of these cases. They reported a major complication rate of 9%; 5% due to epicardial bleeding, and 4% due to ablation itself including pulmonary emboli, steam pop causing pericardial effusion, cardiogenic shock, AV block, and groin haematomas. There were no procedure-related deaths.

The authors stressed the importance of crude patient selection with consideration of the following safety points:

- Pericardial access and mapping is difficult in patients who have had prior cardiac surgery due to adhesions. Coronary artery bypass grafts may also become damaged during the procedure. The above mentioned safety study failed to obtain access or adequate mapping in 85% post cardiac surgery patients [Sacher et al].
- Pericardial puncture is facilitated by a Tuohy needle and contrast medium to confirm position. Sacher et al reported a 20% RV puncture rate but only 3% resulted in significant bleeding.
- Irrigated ablation catheters were used with haemodynamic monitoring and intrapericardial fluid drainage every 15-20 mins throughout the procedure.
- Coronary angiography is useful pre-ablation in preventing coronary damage. Some centers use cryoablation if targets are in close proximity to coronary arteries.
- The risk of downstream constrictive pericarditis is not known. There were no cases identified in the 2-year follow up period of this study.

Mortality & Predicting Outcomes
Procedure-related mortality rate across publications by 19 experienced centers averaged 0.5% [2].

Peichl et al performed univariate analysis on their patient group and found that the most significant risk factors for complications were age, reduced LV systolic function, and elevated serum creatinine [3]. Interestingly they also noted that procedures that started after 2pm were associated with twice the complication risk (10% vs 5%).

Certainly VT ablation has progressed significantly since first introduction. Idiopathic VT and prophylactic structural heart VT carries a favourable safety profile compared to treatment of recurrent VT in structural heart disease populations. In fact their safety profiles are comparable to other low risk ablation procedures such as SVT ablation. Nevertheless structural heart disease VT data suggests it remains an adjunctive therapeutic option in severely symptomatic patients where antiarrhythmic therapy has failed or is not tolerated. A robust and simple risk analysis tool is required for clinicians to make informed decisions of who should undergo the procedure.

REFERENCES
1) Belhassen B, Miller HI, Geller E, Laniado S: Transcatheter electrical shock ablation of ventricular tachycardia. J Am Coll Cardiol 1986;7:1347-1355
2) Wissner E, Stevenson W, Kuck K: Catheter ablation of ventricular tachycardia in ischaemic and non-ischaemic cardiomyopathy: where are we today? A clinical review. Eur Heart J. 2012 Jun;33(12):1440-50
3) Peichl P, Wichterle D, Pavlu L, Cihak R, Aldhoon B, Kautzner J: Complications of catheter ablation of ventricular tachycardia: a single-center experience. Circ Arrhythm Electrophysiol. 2014 Aug;7(4):684-90
4) Bohnen M, Stevenson WG, Tedrow UB, Michaud GF, John RM, Epstein LM, Albert CM, Koplan BA: Incidence and predictors of major complications from contemporary catheter ablation to treat cardiac arrhythmias. Heart Rhythm. 2011 Nov;8(11):1661-6
5) Stevenson W et al: Irrigated radiofrequency catheter ablation guided by electroanatomic mapping for recurrent ventricular tachycardia after myocardial infarction: the multicenter thermocool ventricular tachycardia ablation trial. Circulation. 2008 Dec 16;118(25):2773-82
6) Mallidi J, Nadkarni GN, Berger RD, Calkins H, Nazarian S: Meta-analysis of catheter ablation as an adjunct to medical therapy for treatment of ventricular tachycardia in patients with structural heart disease. Heart Rhythm. 2011 Apr;8(4):503-10
7) Reddy V et al: Prophylactic catheter ablation for the prevention of defibrillator therapy. N Engl J Med. 2007 Dec 27;357(26):2657-65.
8) Kuck KH et al: Catheter ablation of stable ventricular tachycardia before defibrillator implantation in patients with coronary heart disease (VTACH): a multicentre randomised controlled trial. Lancet. 2010 Jan 2;375(9708):31-40
9) Calkins H et al: Catheter ablation of ventricular tachycardia in patients with structural heart disease using cooled radiofrequency energy: results of a prospective multicenter study. Cooled RF Multi Center Investigators Group. J Am Coll Cardiol. 2000 Jun;35(7):1905-14.
10) Nayyar S et al: Venturing into ventricular arrhythmia storm: a systematic review and meta-analysis. Eur Heart J. 2013 Feb;34(8):560-71.
11) Sacher F et al: Epicardial ventricular tachycardia ablation a multicenter safety study. J Am Coll Cardiol. 2010 May 25;55(21):2366-72

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