Ablation of Ventricular Tachycardia Associated With Nonischemic Cardiomyopathy

Key Points

Mapping

Entrainment mapping focusing on sites with concealed entrainment, pace mapping, electrogram-mapping focusing on sites with fractionated electrograms and isolated potentials

Ablation Targets

Myocardial fibers within scar tissue

Special Equipment

Preprocedural magnetic resonance imaging to assess for presence and location of scar tissue
Intracardiac echocardiography to assess for intracardiac structures like papillary muscles, location of scar or aneurysms

Sources of Difficulty

Intramural and epicardial location or the arrhythmogenic substrate

Disease Spectrum

The term nonischemic cardiomyopathy ( NICM ) encompasses a spectrum of diseases, including dilated idiopathic cardiomyopathy, cardiac sarcoidosis, and other forms of myocarditis as well as Chagas disease, hypertrophic cardiomyopathy, amyloidosis, valvular heart disease, and arrhythmogenic right ventricular cardiomyopathy/dysplasia (ARVC/D). Most of these disease entities result in myocardial scar formation, thus creating a substrate for the subsequent development of ventricular arrhythmias. Ventricular tachycardias are among the many clinical manifestations of disease in patients with NICM. This chapter focuses on ventricular tachycardia (VT) ablation in patients with idiopathic dilated cardiomyopathy, myocarditis, cardiac sarcoidosis, ARVC/D, hypertrophic cardiomyopathy, and Chagas disease.

Etiology and Characterization of the Arrhythmogenic Substrate

A comprehensive evaluation using multiple diagnostic modalities is necessary to identify the etiology and to characterize the arrhythmogenic substrate in patients with NICM ( Table 31.1 ). Commonly no specific underlying disease process can be identified and idiopathic dilated cardiomyopathy may be present, which can be often a sequela of myocarditis. Cardiac magnetic resonance imaging (MRI) with delayed enhancement (DE-MRI) is an important modality that can offer key information regarding the etiology and the arrhythmogenic substrate in NICM. Scar distribution in the cardiac MRI can indicate disease-specific patterns of scarring that may be helpful in directing further workup in clarifying the underlying etiology of cardiomyopathy. It must be mentioned, however, that sarcoidosis can present diagnostic challenges and there is no test that can definitively rule out cardiac sarcoidosis. The workup for sarcoidosis requires biopsies (cardiac or noncardiac) to assess for the disease-specific histology of noncaseating granulomas. A scar pattern in the DE-MRI with multifocal areas of delayed enhancement in the right ventricle (RV) with basal septal involvement suggests, but does not prove, the presence of cardiac sarcoidosis.

TABLE 31.1

Arrhythmic Syndrome Diagnostic Criteria

Idiopathic Dilated Cardiomyopathy	Cardiomyopathy without obvious etiology despite diagnostic workup
Myocarditis	Viral infection of the myocardium resulting in acute or chronic myocarditis that may heal with or without sequelae (scar)
Sarcoid Heart Disease	Sarcoidosis involving the myocardium; can be part of systemic form or can be limited to the heart
Arrhythmogenic right ventricular cardiomyopathy/dysplasia	Predominantly right ventricular dilation and dysfunction; task force criteria for diagnosis
Hypertrophic cardiomyopathy	Cardiomyopathy associated with hypertrophy without obvious cause
Chagas Disease	Cardiomyopathy caused by infection with the parasite Trypanosoma cruzi

It is important to keep in mind that frequent premature ventricular complexes (PVCs) may cause a reversible form of NICM. In patients who present with a cardiomyopathy of unclear etiology and who have a PVC burden greater than 10% to 20%, catheter ablation of the PVCs is appropriate and may result in improvement or even reversal of cardiomyopathy. Most often, there is no delayed enhancement in the cardiac MRI, indicating that there is no other myopathic process present.

Most VTs in patients with NICM are caused by reentry originating within scar tissue. DE-MRI is used as the gold standard for imaging of scar tissue ( Fig. 31.1 ). Exact localization of the scar is of particular importance in patients with NICM. In patients with ischemic cardiomyopathy, the scar is typically subendocardially located giving rise to VTs that can be reached from the endocardium. In NICM, on the other hand, intramural VT as well as epicardial VTs are more frequent and may result in procedural failure if an endocardial approach only is used.

Fig. 31.1, Stack of short axis views of a delayed-enhanced magnetic resonance image in a patient with nonischemic cardiomyopathy from base (right) toward apex (left). There is predominantly epicardial uptake of gadolinium, indicative of scar tissue ( yellow dotted lines ) in the basolateral left ventricle.

Scar tissue can be differentiated from normal myocardium on T1-weighted MR images because of delayed contrast enhancement and the fact that gadolinium contrast agents shorten the longitudinal relaxation time (T1). Gadolinium contrast agents (gadolinium chelates) are unable to cross the intact cell membrane, and in the normal myocardium the tissue volume is mainly intracellular. Enhancement of the myocardium several minutes after intravenous injection of a gadolinium chelate indicates accumulation of contrast material in areas where the extracellular space is increased. In the setting of myocardial necrosis or inflammation, disruption of myocyte membranes causes an increased distribution space for gadolinium. In the setting of chronic scar formation, collagenous scar tissue has replaced the necrotic tissue, and the increase in interstitial tissue increases the volume of distribution for the contrast agent, resulting in hyperenhancement.

Disease-Specific Arrhythmogenic Substrate

The MRI helps to identify the arrhythmogenic substrate and can be important in planning an effective ablation procedure.

Idiopathic Dilated Cardiomyopathy

Reports focusing on the histologic findings in patients with dilated cardiomyopathy as well as conduction studies in these patients have demonstrated that the architecture, more than the amount of fibrosis, impacts on conduction velocity. Discontinuous conduction resulting in unidirectional block can occur, especially in the presence of long strands of fibrosis and dense replacement fibrosis. The presence of scar by DE-MRI has been correlated with the spontaneous occurrence of VT as well as the inducibility of VTs, and with outcome in patients with NICM even in the presence of preserved left ventricular (LV) function. The hallmark of idiopathic dilated cardiomyopathy is the presence of mid-wall delayed enhancement. In a study by Neilan et al., intramural scarring was present in 52% of the patients. Predominant epicardial scarring was observed in 26%, and focal scarring involving insertion points was seen in 20% of the patients. There is a predominance of perivalvular scarring, but the anteroseptal and inferolateral left ventricle have also been involved in the arrhythmogenic substrate in these patients.

Myocarditis

Acute myocarditis most often heals completely but can result in scarring and the development of cardiomyopathy. Arrhythmias are uncommon in acute myocarditis but can develop during long-term follow-up as a result of myocardial scarring. In chronic myocarditis, there is intramural or epicardial scarring in addition to evidence of inflammation by endomyocardial biopsy or positron emission tomography (PET) imaging. In the majority of patients with ventricular arrhythmias, the scar is located intramurally, whereas epicardial scarring was present in about one fourth of patients. The scar pattern is similar in patients presenting with VT late after myocarditis. It should be noted that it is not possible to distinguish between idiopathic dilated cardiomyopathy and healed myocarditis as the scarring pattern can be similar, with predominantly intramural and epicardial distribution.

Cardiac Sarcoidosis

Sarcoidosis can affect the myocardium in the form of an infiltrative cardiomyopathy with acute or chronic inflammation and subsequent scarring. The Japanese Health and Welfare Ministry criteria have been traditionally used to establish the criteria for cardiac involvement. More recently, the Heart Rhythm Society published a consensus statement including updated criteria for the diagnosis of cardiac sarcoidosis ( Table 31.2 ). A positive biopsy for the presence of noncaseating granulomas is key for making the diagnosis of sarcoidosis, and in the absence of a positive myocardial biopsy, the presence of specific criteria can be used to make a probable diagnosis of cardiac involvement provided noncaseating granulomas from an extracardiac source have been demonstrated. Hence, the diagnosis of isolated cardiac sarcoidosis is difficult and requires a positive cardiac biopsy; not surprisingly, the prevalence of isolated cardiac sarcoidosis is likely underestimated and requires a heightened index of suspicion. Granulomas start within the myocardium and reach the endocardium or epicardium via extension of the initial inflammatory lesions. In cardiac sarcoidosis, patchy, multifocal involvement of the basal septum, but also patterns involving predominantly the LV epicardium or the RV, have all been described. Ventricular arrhythmias can arise in the acute inflammatory setting or in the chronic state when inflammatory tissue has been replaced by scar tissue. The location of scar determines the origin of ventricular arrhythmias. The presence and extent of delayed enhancement is a known predictor of adverse outcomes in patients with cardiac sarcoidosis. Similarly, the presence of F-fluorodeoxyglucose (FDG) uptake in PET imaging in patients with cardiac sarcoidosis identifies patients at higher risk of death or VT. Locally increased FDG uptake in the absence of a positive biopsy for sarcoidosis has been described, and the term arrhythmogenic inflammatory cardiomyopathy has been coined for this condition.

TABLE 31.2

Heart Rhythm Society Diagnosis Criteria for Cardiac Sarcoidosis

1.
Histologic Diagnosis
Cardiac sarcoidosis is diagnosed in the presence of noncaseating granuloma

2.
Clinical Diagnosis
Cardiac sarcoidosis is probable ^a if:
- (a)
  There is extracardiac sarcoidosis
- and
- (b)
  One or more of the following criteria:
  - -
    Steroid ± immunosuppressant responsive cardiomyopathy or heart block
  - -
    Unexplained EF <40%
  - -
    Unexplained VT (sustained or induced)
  - -
    Advanced AV block
  - -
    Patchy uptake on cardiac PET (in a pattern consistent with cardiac sarcoidosis)
  - -
    Late gadolinium enhancement on MRI (in a pattern consistent with cardiac sarcoidosis)
  - -
    Positive gallium uptake (in a pattern consistent with cardiac sarcoidosis)
  - and
- (c)
  Other causes for cardiac manifestations have been excluded

AV , Atrioventricular; EF , ejection fraction; MRI , magnetic resonance imaging; PET , positron emission tomography; VT , ventricular tachycardia.

a “Probable” indicates that there is sufficient evidence for making the diagnosis of cardiac sarcoidosis.

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