Abstract
Ventricular tachycardia (VT) is an outcome-defining complication in the natural history of non-ischemic cardiomyopathies, including idiopathic dilated cardiomyopathy, cardiac sarcoidosis, arrhythmogenic right ventricular cardiomyopathy, among others. While a number of scar-based approaches towards mapping and ablation can be utilized, the ablative treatment of VT in these patients can be challenging. It commonly requires combined endocardial and epicardial mapping/ablation, and is associated with high rates of incomplete success, long-term arrhythmia recurrences and need for multiple procedures. This is largely due to the fact that the arrhythmogenic substrate is frequently intramural and/or epicardial. Therefore, accurate characterization of the substrate with pre-procedural imaging can help optimize procedural planning, including determining the need for epicardial mapping. In this chapter we discuss diagnostic criteria, characterization of the arrhythmogenic substrate, pre-procedural planning, ablation approaches and end points, and disease-specific considerations.
Keywords
ablation, diagnostic criteria, mapping, nonischemic cardiomyopathy, target sites, ventricular tachycardia
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.
| 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.
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.
|
|
a “Probable” indicates that there is sufficient evidence for making the diagnosis of cardiac sarcoidosis.
Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia
The Task Force Criteria for the diagnosis of ARVC/D were updated in 2010 ( Table 31.3 ). The disease process starts in the epicardial RV where fibrofatty tissue replaces myocardial tissue, whereas DE-MRI also demonstrates scar tissue in the RV in this cardiomyopathy and its the presence correlates with inducibility of VT. Interestingly, limited data exists on the use of MRI in defining the arrhythmogenic substrate in patients with ARVC. Possible reasons include difficulties in imaging the thinner wall of the RV as well as differences in optimal inversion times of the RV if nulling is performed based on the left ventricle. In a study of 23 patients with ARVC/D who underwent both DE-MRI and endocardial voltage mapping, the DE-MRI failed to detect areas of scar in about half of the areas with low endocardial voltage, especially in the inferobasal RV. Of note, the involvement of the LV in patients with ARVC/D has been well known and may be present in up to three-quarters of the patients. Intramyocardial LV fat as observed in multidetector computed tomography imaging was the most sensitive imaging finding in a recent series, but the correlation with low voltage was poor.
| Right Ventricular Dysfunction and Structural Changes | |
| Major | Regional RV akinesis, dyskinesis, or aneurysm (echo, MRI, right ventriculography) and 1 or more criteria indicating RV dysfunction/dilatation by
|
| Minor | Regional RV akinesis, dyskinesis, or aneurysm (echo, MRI, right ventriculography) and 1 or more criteria indicating RV dysfunction/dilatation by
|
| Tissue Characterization | |
| Major | Residual myocytes < 60% by morphometric analysis (or < 50% if estimated), with fibrous replacement of the RV free wall myocardium in ≥1 sample, with or without fatty replacement of tissue on endomyocardial biopsy |
| Minor | Residual myocytes 60%–75% by morphometric analysis (or 50%–65% if estimated), with fibrous replacement of the RV free wall myocardium in ≥1 sample, with or without fatty replacement of tissue on endomyocardial biopsy |
| Repolarization Abnormalities | |
| Major | Inverted T waves in right precordial leads (V1, V2, and V3) or beyond in individuals. > 14 years of age (in the absence of complete right bundle branch block QRS 120 ms) |
| Minor |
|
| Depolarization/Conduction Abnormalities | |
| Major | Epsilon wave (reproducible low-amplitude signals between end of QRS complex to onset of the T wave) in the right precordial leads (V1–V3) |
| Minor |
|
| Arrhythmias | |
| Major |
|
| Minor |
|
| Family History | |
| Major |
|
| Minor |
|
Hypertrophic Cardiomyopathy
The presence of delayed enhancement in patients with hypertrophic cardiomyopathy has been reported to correlate with the presence of ventricular arrhythmias. Ventricular tachycardia mapping and ablation procedures have been reported in a few patients with hypertrophic cardiomyopathy. The value of MRI for correlation of the location of scar tissue with the origin of ventricular arrhythmias remains to be determined, however. Although no series of patients has been reported in which MRI was used systematically to map VT in patients with hypertrophic cardiomyopathy, MRI has been helpful to indicate the arrhythmogenic substrate in a few patients ; furthermore, the finding that many VTs have critical areas in the zone where the interventricular septum inserts into the left–right ventricular junction corresponds to prior reports from MRI data indicating that this is often an area of fibrosis in patients with hypertrophic cardiomyopathy.
Chagas Cardiomyopathy
The arrhythmogenic substrate in Chagas cardiomyopathy typically involves the inferolateral left ventricle. The value of scar imaging in identifying the arrhythmogenic substrate in this condition has not been systematically analyzed. Limited data with the use of DE-MRI suggest that more than two-thirds of patients have detectable myocardial fibrosis. In one series, in the majority of cases (53%) the scar was endocardial, indistinguishable from postinfarction scarring. In only 12% of patients, the scarring was limited to the epicardium, and in 35% it was intramural. Nevertheless, during simultaneous endocardial and epicardial electroanatomic mapping, the epicardium appears to harbor larger low-voltage areas compared with the endocardium.
Preablation Workup and Procedural Planning
Different mapping strategies are possible as an initial approach in patients with NICM and VT. If endocardial mapping does not yield an effective ablation site, a transcutaneous subxiphoid puncture to enter the pericardial space can be performed at a separate session (stepwise approach). An alternative option to the stepwise approach is to enter the pericardial space during the first ablation procedure, before the administration of heparin, in all patients with NICM. Yet another approach is a substrate-oriented approach that is guided by imaging and the location of the arrhythmogenic substrate, that is, the scar tissue. The location of the scar tissue often corresponds to areas critical for VT circuits in these patients. The latter approach has the advantage that it only exposes patients to the increased periprocedural risk of pericardial puncture and epicardial mapping if the arrhythmogenic substrate either involves the epicardium or the intramural free wall. Of note, an epicardial ablation is unlikely to eliminate a focus from the interventricular septum, and in these patients, both left and right aspects of the septum may need to be mapped and ablated for elimination of VT. Unfortunately, most patients presenting for VT ablation have implanted implantable cardioverter-defibrillators (ICDs), and in the past MRIs were contraindicated (and are still not performed at many institutions) in patients with implanted cardiac devices, despite mounting evidence that MRIs can be safely performed in such patients with adequate precautions. Mapping and ablation procedures where scar was identified with preprocedure DE-MRI in patients with implanted devices have been carried out despite artifact generated by the ICD generator. In addition to DE-MRI, multidetector cardiac computed tomography (MDCT) can also help in characterizing the arrhythmogenic substrate by identifying myocardial wall thinning. The feasibility of integrating DE-MRI and/or MDCT imaging data to the electroanatomic map has recently been demonstrated and has the potential to impact procedural management and outcomes in scar-related VT.
It is helpful to review all available 12-lead electrocardiograms (ECGs) and ICD-stored electrograms of the VT(s) before the ablation procedure, which can serve as reference for induced VTs during the ablation procedure. The 12-lead ECG has important information and may be helpful in deciding whether an arrhythmia may have an epicardial origin in the absence of a cardiac MRI. Before the ablation procedure, a LV thrombus needs to be ruled out by transthoracic echocardiography or cardiac CT.
Selection of Target Sites for Ablation
Reentry is the most common mechanism of VT, and therefore a mapping strategy similar to postinfarction VT can usually be used ( Fig. 31.2 ). Entrainment mapping, however, can only be performed for hemodynamically tolerated VTs, unless hemodynamic support is provided by assist devices. About one-third of patients have tolerated VTs that can be mapped with entrainment mapping. During the procedure, multipolar catheters are positioned in the high right atrium, the His bundle position, and the right ventricular apex. It is important to have a catheter at the His position to assess for the presence of bundle branch reentry tachycardia. The right ventricular catheter is positioned at the right ventricular apex, and the postpacing interval at this site is also helpful in diagnosing bundle branch reentry tachycardia, especially if the His deflection is difficult to appreciate.
Programmed right ventricular stimulation is used to induce VT. An electromagnetic mapping system is used in combination with an open-irrigation-tip catheter for mapping, navigation, and ablation. It is also helpful to use an intracardiac echo probe to identify the papillary muscles, aneurysms, or even epicardial scar to direct the mapping catheter in the correct direction.
Endocardial activation and/or entrainment mapping (see Fig. 31.2 ) is performed during VT if the VT is tolerated hemodynamically ( Table 31.4 ). For VTs resulting in hemodynamic compromise, pace mapping and voltage mapping are performed at the same locations. VTs originating from an intramyocardial focus can be particularly challenging because both entrainment mapping and pace mapping may only be helpful to get close to the epicardial or endocardial breakthrough sites. In case of hemodynamic compromise, percutaneous assist devices can maintain hemodynamic stability for a period of time that may be sufficient to more precisely identify breakthrough sites. However, the use of hemodynamic support has not improved outcomes and may increase periprocedural complications, because large bore arterial access is required. As each point is collected for the voltage map, pacing is performed at sites with low voltage (bipolar voltage amplitude of <1.5 mV), isolated potentials, or fractionated electrograms. Isolated potentials are particularly helpful in postinfarction patients to guide radiofrequency (RF) ablation ( Fig. 31.3 ). Although their prevalence is lower in patients with NICM, it appears that they are equally, if not more, helpful in NICM patients. A good pace map (defined as ≥10/12 matching leads between the pace map and the targeted VT) at a site where there is an isolated potential is useful for identifying a critical component of the reentry circuit (see Fig. 31.3 ). A good pace map at a site without an isolated potential is a less specific indicator of a critical site for ablation. Histologic analysis adjacent to sites where matching pace maps were identified and where ablation was performed indicate that diffuse fibrosis patterns are present in the area composing the arrhythmogenic substrate.
| Target Site | |
|---|---|
| During sinus rhythm | Isolated potential |
| Matching pace map (≥10/12 leads) | |
| During ventricular tachycardia | Concealed entrainment |
| Isolated diastolic potentials | |
| Fractionated electrograms |
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
