Catheter ablation versus Amiodarone to prevent future shock episodes in patients with a defibrillator and a history of a myocardial infarction.

Ventricular tachycardia or fibrillation is a rhythm disturbance commonly
encountered among patients with coronary artery disease. lt is the
primary tachyarrhythrmia responsible for nonfatal cardiac arrest among
patients with a history of myocardial infarction. VT after myocardial
infarction commonly arises from a relatively discrete and heterogeneous region
of left ventricular (LV) myocardium within or bordering the infarct zone (1,2).
Over the past two decades, therapeutic approaches have included pharmacological
suppression or surgical excision of the arrhythmogenic focus (3-5). Because of
the unsatisfactory results provided by these approaches, an alternative
solution in common use during the past years has been the implantable
cardioverter-defibrillator (6,7). This method does not eliminate the
tachyarhythmia but, instead, attempts to terminate it by delivering pacing
stimuli or countershocks. Although most patients can adapt to its presence, it
has both considerable cost and the potential for significant long-term
psychological impact on the recipient. ICD therapy has a significant positive
impact on long-term survival in patients with an impaired LV function, with or
without history of (inducible) VT*s (3,8-12). Increasing numbers of patients
with CAD are treated with an ICD. One of the major concerns after implantation
is management and prevention of ICD shocks caused by (unstable) ventricular
tachycardia (VT) or ventricular fibrillation (VF). Recurrent ICD shocks lead to
a decreased quality of life and increased hospitalisation and costs (13,14).
Clinically significant anxiety and depression as a result of recurrent ICD
shocks may occur in more than 50% of patients (15-17). Repeated ICD shocks
within a short time interval, known as an ICD *storm,* occur in 10 to 25% of
patients. (18,19)
Radiofrequency ablation and/or antiarrhythmic medication are both used to
prevent recurrences of shock therapy. Catheter ablation of VT requires that the
reentry circuit of the VT be accurately pinpointed. This is performed using a
catheter introduced into the left ventricle. Through a process known as
endocardial mapping, the catheter is methodically guided throughout the left
ventricular endocardial surface during tachycardia while observing the
characteristics of the sequentially recorded electrograms representing local
endocardial activation. Specific features of electrograms denoting the site of
origin of the VT and the response to certain pacing maneuvers have been
described (20-23) The delivery of radiofrequency energy at the site of origin
can eliminate the VT. Catheter ablation is effective in the treatment of stable
VT (24- 32) as well as unstable VT (33-36). Modern ablation techniques
(substrate mapping and ablation) which use the electroanatomic mapping system
CARTO (37-39) allow the ablation of hemodynamically poorly tolerated VT.
Recently, prophylactic substrate-based catheter ablation was found to reduce
the incidence of ICD therapy in patients with a history of myocardial
infarction who received ICDs for the secondary prevention of sudden death.(40)
In a subgroup analysis of this study, revascularization of patients was
correlated with increased effect of catheter ablation in comparison with
placebo. This might be due to a decrease in ablation effectiveness in patients
with myocardial ischemia. Long-term medical therapy with amiodarone is an
effective therapy to prevent ICD shock therapy, but it is known to coincide
with multiple important side effects (41). Therefore, long-term amiodarone
therapy is debatable. However, no comparison between catheter ablation and
medical therapy was made, and only secondary prevention and mostly
non-revascularized patients were included.

The main objective of this study is to compare the occurrence of next ICD shock
therapy for VT or VF in patients with hospital presentation for an ICD shock
therapy for VT or VF, with a history of a myocardial infarction, between
patients randomized to substrate based ablation or amiodarone.

A prospective, randomized study will be conducted in a single center: hospital
Isala Klinieken, location de Weezenlanden, Zwolle, the Netherlands. Patients
with a prior myocardial infarction, and appropriate ICD therapy will be
included into the study.

1 group takes daily 200 mg amiodarone
1 group undergoes ones a catheter ablation

The ablation procedural mortality varies between 0-4.8 % in the largest
reported series (25,27,31,32,33,35,46).

The most serious risks of systemic arterial embolization which can cause
myocardial infarction, stroke, cardiac perforation or tamponade occurred in 3%
of patients in recent series (25-28,31). Of 52 patients from one center there
was one death in the perioperative period due to acute myocardial infarction
(25). Damage to cardiac valves, damage to the normal cardiac conducting system
requiring a permanent pacemaker, damage to vasculature, and deep venous
thrombosis can also occur, but are infrequent. Initiation of ventricular
tachycardia is required. This can produce hypotension and may require
electrical cardioversion with attendant musculoskeletal discomfort. Procedures
are performed under sedation or general anesthesia. The risks of sedation
include hypoventilation, hypotension, and allergic reactions to the
medications. Fluoroscopy will be used for initial catheter positioning. Precise
identification of mapping catheter position with the CARTO system is expected
to help locate and repeatedly position the catheter at desirable target sites
for ablation. The systems allows identification of catheter position without
fluoroscopy and will probably reduce fluoroscopy exposure in this study.
Mapping during hemodynamically stable sinus rhythm is performed routinely
during catheter ablation procedure.

Radiofrequency current may cause occlusion of a coronary artery, either by
direct thermal damage, spasm, or thrombosis. Experience at numerous centers
suggests that the risk of coronary occlusion is less than 0.5%. Coronary
arterial occlusion could produce myocardial infarction, angina or death. Should
occlusion of a coronary artery occur for any reason, the physician will attempt
to restore coronary blood flow through pharmacological, catheter and/or
surgical intervention as medically indicated.

The application of radiofrequency current close to the AV node or His bundle
could damage the normal AV conduction system, producing complete heart block
and requiring permanent ventricular pacing. If this should become necessary, it
is possible to incorporate this function into the ICD which is to be implanted.

A thrombus may form on the ablation electrode during the application of
radiofrequency current usually indicated by an impedance rise. The thrombus
might become dislodged and embolize to produce a stroke, myocardial infarction,
or other ischemic injury. The risk of an embolus is reduced by quickly
terminating the application of current after an impedance rise, which limits
the size of the coagulum on the electrode.

Thrombus formation on the endocardium following ablation may produce an
arterial or pulmonary embolus, This risk may be reduced by the use of aspirin
or other anticoagulant therapy, at the discretion of the investigator.

Cardiac perforation may result from catheter manipulation or application of
radiofrequency current (risk is <1%). This may result in cardiac tamponade and
may require percutaneous pericardial drainage or surgical repair. Significant
hemodynamic compromise can result in neurologic injury or death.

lnjury to a cardiac valve may result from catheter manipulation or the
application of radiofrequency current (risk < 1 %). This may produce valvular
insufficiency and possibly require surgical valve replacement.

Radiation exposure during the fluoroscopic imaging of the catheters may result
in an increase in the lifetime risk of developing a fatal malignancy (0. 1 %)
or a genetic defect in offspring (0.002%).

Other potential complications that may result from catheter insertion and
manipulation as part of the prerequisite electrophysiology study and mapping
procedure include:

Allergic reaction to the local anesthetic, sedatives, x-ray dye, heparin,
protamine, or other agents administered during the procedure (risk < 1 %).

Arterial or venous injury, including arterial dissection, thrombosis, occlusion
or hemorrhage at the catheter insertion sites or at other sites along the
vessels (risk < 1 %). This may produce hemorrhage, hematoma or ischemic injury
to an extremity or major organ.

Hemorrhage as a result of anticoagulation (risk <0.5%) which may require
transfusion.

Infection, either at the catheter insertion site or systemically, including
endocarditis and septic emboli (risk < 0.5 %). This risk can be minimized by
using standard aseptic technique and, when indicated, by the use of antibiotic
agents.