Naomi J. Kertesz, MD
The patient is a 26-year-old man with past medical history of tetralogy of Fallot, status post complete repair at 9 months of age with a large transannular RV outflow patch in addition to ASD and VSD closure. The repair included a ventriculotomy. This is the only surgical intervention BW has undergone.
BW has had palpitations for the past 5 years. He also describes 4 syncopal episodes over the past 7 years. All episodes were associated with painful stimuli. He was given an event monitor that demonstrated SVT at 150 bpm (Figure 26-1). As part of his normal follow-up he underwent an MRI and was found to have right ventricular ejection fraction of 36% and a right ventricular end diastolic volume of 161 mL/m2 (Figure 26-2). As part of a prepulmonary valve replacement protocol, he underwent a hemodynamic catheterization (Figure 26-3) and programmed ventricular stimulation (Figure 26-4). There was reproducibly inducible monomorphic VT with double and triple extra stimuli at baseline from the RV apex that was able to be pace-terminated (Figures 26-5 and 26-6). The VT circuit was mapped using 3-D mapping, and an array catheter and was found to be a macroreentrant circuit around the right ventricular free wall which corresponded to his prior right ventriculotomy site (Figure 26-7). He underwent a slow pathway modification for his atrioventricular node reentry. He went to the operating room the following day and underwent surgical pulmonary valve replacement and cryoablation to isolate the area of the right ventricular outflow tract. He underwent a repeat electrophysiology study 8 months later and had no inducible arrhythmias with or without isoproterenol.
FIGURE 26-1 Transtelephonic monitor (TTM) tracing demonstrating SVT. At first glance, the TTM demonstrates a wide QRS tachycardia. On further inspection, the QRS in sinus rhythm (*) is the same as the QRS in tachycardia (**). Patients with congenital heart disease commonly have a bundle branch block at baseline due to VSD repair. Therefore, it is important to determine not only the QRS duration but to determine whether the morphology is the same or different as that which is seen in sinus rhythm.
FIGURE 26-2 MRI of patient with TOF. This patient has a dilated RV and PA due to severe pulmonary regurgitation following TOF repair. Many patients require pulmonary valve replacement during late adolescence or early adulthood.
FIGURE 26-3 Cardiac catheterization diagram. The ventriculotomy incision was used to enlarge the RVOT, pulmonary valve, and MPA.
FIGURE 26-4 Baseline ECG. Note the wide QRS and the right bundle branch block which is classic in patients following TOF repair.
FIGURE 26-5 Surface electrograms of VT induction. Note the wide QRS and that it is different than the QRS in sinus rhythm.
FIGURE 26-6 Burst pacing used to terminate VT. Note onset of pacing as seen as S1 on the Stim channel. Note the change in QRS morphology as pacing captures the ventricle.
FIGURE 26-7 AP and lateral projections of right ventricle. In the image on the left, the white dots represent area of scar from ventriculotomy incision, and the blue arrows represent the circuit of the VT traveling between two areas of scar.
• Congenital heart disease (CHD) is the most common form of birth defect with an incidence of 8 significant defects per 1000 live births.1 Due to advances in both diagnosis and treatment the majority of children live to adulthood. Over one million adult congenital heart disease patients are living in the United States.2 There are now a greater number of adults than children with congenital heart disease living in the United States.3
• Forty-five percent of these adults have simple defects (atrial septal defect, ventricular septal defect, valve stenosis).
• Forty percent have moderately complex heart disease (tetralogy of Fallot).
• Ventricular arrhythmias are rare among CHD patients during the first or second decade of life.
• Patients at highest risk for developing ventricular tachycardia are those who have undergone a ventriculotomy or patching of certain ventricular septal defects.
• Historically sudden cardiac death (SCD) in patients with CHD has been observed most often among patients with TOF and transposition of the great arteries (TGA) who are status post a Mustard or Senning operation4 (Figure 26-8).
FIGURE 26-8 Transposition status post atrial baffle repair (Mustard or Senning repair). Note that the SVC and IVC blood is directed to the mitral valve and left ventricle, which is connected to the pulmonary artery. The pulmonary veins, not shown, are directed to the right ventricle, which is connected to the aorta.
• However, due to advances in surgical technique and timing of repair, a substantial shift in the epidemiology of mortality in CHD patients has occurred over the past 25 years. A comparison of mortality due to CHD between 1987 and 1988 and between 2004 and 2005 showed that the overall mortality rate had decreased by 31%.5 There has been a 40% reduction in annualized death rates for TOF and a 71% reduction for TGA between 1979 and 2005 in the United States.6 In patients with noncyanotic defects such as ventricular septal defects and coarctation of the aorta, arrhythmias were the leading cause of death before 1990, but after 1990 myocardial infarction was the leading cause of overall mortality. In those with cyanotic defects, ie, TOF and TGA, arrhythmias remain the leading cause of late death.
• Sustained VT appears to be the single biggest contributor to the 2% per decade incidence of sudden death in TOF.2
ETIOLOGY AND PATHOPHYSIOLOGY
• There are two main causes of ventricular arrhythmias in congenital heart disease. One is the result of the surgical scars from the repair, and the other is due to long-standing abnormal hemodynamics resulting from volume or pressure overload. Understanding the causes of the arrhythmia is only half the battle. One should understand that the surgical repairs have changed over time and the age at which these repairs are performed has also changed. This has contributed to the changing incidence of sudden cardiac death.
• The mechanism for VT resulting from scar is reminiscent of the intra-arterial reentry atrial tachycardia (scar atrial flutter). It is due to a macroreentrant circuit involving narrow conduction corridors defined by the regions of surgical scar and natural conduction barriers such as the rim of a ventricular septal defect and the edge of a valve annulus. Tetralogy of Fallot is a classic example of congenital heart disease that results in this type of VT. The prevalence of VT after TOF repair has been estimated to be between 3% and 14%.2
• Ventricular arrhythmias can also develop due to long standing hemodynamic overload, which causes advanced ventricular dysfunction or hypertrophy. Examples of CHD lesions that can eventually lead to this myopathic variety of VT include aortic valve disease; LTGA or DTGA following atrial repair when the right ventricle is the systemic ventricle; severe Ebstein anomaly (Figure 26-9); single ventricle physiology (Figure 26-10); and Eisenmengers syndrome.2
FIGURE 26-9 MRI of Ebstein anomaly. Note large amount of atrialized right ventricle due to displaced tricuspid leaflets. The functional RV is now significantly smaller due to a large part becoming atrialized (above the TV).
FIGURE 26-10 Single ventricle patient status post-Fontan procedure. Note SVC and IVC with direct connection to pulmonary artery with no intervening ventricle. Note the large dilated single ventricle.
DIAGNOSIS AND MANAGEMENT
• While sustained VT can lead to sudden cardiac death or syncope, some patients present with palpitations. As many of them have an underlying bundle branch block, it is important to realize that the presence of a wide QRS tachycardia does not mean it is ventricular in etiology. Alternatively, if a patient does not faint, it does not mean that it is SVT. Distinguishing VT from SVT can be challenging in young adults in whom a baseline ECG is not available. Due to the relatively healthy AV node, it is not uncommon for there to be one-to-one ventriculoatrial (VA) conduction retrograde in VT (Figure 26-11). Adenosine and/or the use of a transesophageal lead can be very helpful to produce transient VA dissociation to prove that the AV node is not part of the arrhythmia circuit (Figures 26-12 and 26-13).
FIGURE 26-11 Wide QRS tachycardia in an 18-year-old with 1:1 VA conduction. This could be either SVT or VT. It is unlikely to be SVT in a patient with TOF because the tachycardia has a LBBB morphology rather than a RBBB.
FIGURE 26-12 Baseline ECG in a 44-year-old with TOF. Note RBBB morphology of QRS.
FIGURE 26-13 Same patient with wide QRS tachycardia. In order to prove the mechanism of tachycardia a transesophageal electrode was placed that demonstrated VA dissociation.
• While patients may present with sustained ventricular arrhythmias, it is far more common for individuals to present with nonsustained VT.
• The value of programmed ventricular stimulation (VSTIM) in patients with CHD was demonstrated by Alexander et al in 1999.7 VSTIM identified a subgroup with significantly increased mortality and sudden arrhythmic events. A negative VSTIM was a favorable prognostic sign; however, the frequency of false-negative studies was high.
• The value of VSTIM was then evaluated in patients following TOF.8 Inducible monomorphic VT and polymorphic VT predicted future clinical VT and SCD. In a multivariate analysis, inducible sustained VT was an independent risk factor for subsequent events (Figure 26-14).
FIGURE 26-14 Value of programmed ventricular stimulation in tetralogy of Fallot. Kaplan-Meier event-free survival curves are plotted and compared according to whether patients did or did not have inducible sustained VT on electrophysiology testing. Those patients with inducible VT had significantly higher risk of either clinical VT or sudden cardiac death. (Reproduced with permission from Kairy P, Landzberg MJ, Gatzoulis MA, et al. Value of programmed ventricular stimulation after tetralogy of Fallot repair. Circulation. 2004;109:1994-2000. Figure 2B:1998.)
• As many patients with TOF have significant pulmonary regurgitation, it was thought that if the underlying hemodynamic abnormalities were corrected the patients would no longer be at risk of SCD. Harrild demonstrated that the incidence of VT or sudden death was not reduced by pulmonary valve replacement and improvement of hemodynamics.9
• Attention was then focused on the determining the indications for primary prevention of sudden cardiac death. The largest study to identify independent predictors of sudden death included 793 patients with repaired TOF from six centers. Four independent predictors were identified: older age at repair, QRS interval of 180 msec or longer, transannular patch, and annual increase QRS interval.10
• In Khairy’s study evaluating VSTIM in TOF, the independent risk factors for inducible VT were age 18 or older at the time of testing, palpitations, prior palliative surgery, modified Lown classification of premature ventricular beats of two or higher, and a CT ratio of 0.6 or higher on CXR.8 Inducible sustained VT had a sensitivity of 77% and specificity of 79.5% in predicting sudden cardiac death or clinical ventricular tachycardia.
• Given the low rate of sudden cardiac death in TOF of 0.15%, the decision of whether to implant an ICD can be difficult. In a study evaluating the role of ICDs in patients with TOF, the only two independent predictors of appropriate shocks were nonsustained VT and a left ventricular end-diastolic pressure higher than 12 mm Hg. A risk score was developed on the basis of regression coefficients of the variables retained in the final multivariate model (Table 26-1). Patients were into low (0-2), intermediate (3-5), and high risk (6-12) groups based on their risk of sudden death as shown in Fig 15.11
TABLE 26-1 Risk Score for Appropriate Implantable Cardioverter-Defibrillator Shocks in Primary Prevention
• The risk of ICD implantation, however, is not zero. When evaluating patients with both ICD and CHD, inappropriate shocks were observed in 30% of patients predominantly because of atrial tachyarrhythmias. Related complications were seen in 29% of patients with ICD implantation.12 In patients with TOF and ICDs, inappropriate shocks were observed in 5.8% of patients per year. Complications other than inappropriate shocks occurred in 30% and were predominantly late-lead related.11
• Risk stratification for sudden death in TOF remains imperfect and incomplete. Figure 26-15 summarizes a generalized algorithmic approach by Khairy et al13 that is based on a quantitative assessment of the current state of knowledge.
FIGURE 26-15 Risk stratification approach by Khairy et al13 in tetralogy of Fallot. Risk score is calculated based on variables in Table 26-1. Based on the risk category, the decision can be made whether an EP study with ventricular extrastimulus protocol would increase the risk of sudden cardic death to justify ICD implantation.
• While there is a great body of literature demonstrating the risk factors associated with sudden death in TOF, this is not true about DTGA status post atrial switch procedure. Currently, the only documented risk factors for sudden death in this population are symptoms of arrhythmia or heart failure or documented atrial flutter or fibrillation. This data makes the decision to place ICDs for primary prevention difficult.
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13. Khairy P, Dore A, Poirier N, et al. Risk stratification in surgically repaired tetralogy of Fallot. Expert Rev Cardiovasc Ther. 2009;7(7):755-762.