New predictors of malignant ventricular arrhythmias in Chagas disease : searching for the holy grail

Of great frequency are also the sudden deaths in the cardiac forms of the disease. This fact constitutes one of the most curious notes in the clinical history of this trypanosomiasis, the lethality of which and number of deaths is really surprising. It being rare for families living in infested zones not to report the loss of one or more of its members in this way. Sometimes they die while still young, in full activity and with an apparently satisfactory state of health. We have heard from sources worthy of trust, manifested surprise by the frequency of these sudden death, verifi ed in middle-aged individuals, in full working conditions; and in our hospital service, we possessobservations of some patients whose demise was from an almost instantaneous death. These, moreover, presented accentuated cardiac syndrome (Carlos Chagas, 1916)(1)

Of great frequency are also the sudden deaths in the cardiac forms of the disease.This fact constitutes one of the most curious notes in the clinical history of this trypanosomiasis, the lethality of which and number of deaths is really surprising.It being rare for families living in infested zones not to report the loss of one or more of its members in this way.Sometimes they die while still young, in full activity and with an apparently satisfactory state of health.We have heard from sources worthy of trust, manifested surprise by the frequency of these sudden death, verifi ed in middle-aged individuals, in full working conditions; and in our hospital service, we possessobservations of some patients whose demise was from an almost instantaneous death.These, moreover, presented accentuated cardiac syndrome (Carlos Chagas, 1916) (1) Since the fi rst descriptions of Chagas disease (ChD), sudden death is considered one of the characteristics and responsible for >50% of the mortality in chagasic patients with heart failure.In this issue of RSBMT, Barbosa et al (2) .highlight several important aspects of the pathogenesis, prognosis, and treatment of ventricular arrhythmias in ChD (2) .Chagas disease has an essentially arrhythmogenic nature characterized by dense and complex ventricular arrhythmias; therefore, ventricular fi brillation likely constitutes the terminal event in most cases of sudden death, which accounts for the majority of deaths in ChD.Chagas cardiomyopathy gives rise to the most intense fi brous reaction amongst all causes of myocarditis, leading to severe disorganization of the myocardial architecture and structure.In addition to the fi brotic substrate, electrical dispersion plays an important role in arrhythmogenesis, and it is caused by areas of slow conduction leading to electrical instability.Myocardial fi brosis and areas of slow electrical conduction result in mechanical alterations in both timing and function.With the development of therapeutic strategies to prevent death from ventricular fi brillation, particularly the use of implantable cardioverter-defi brillators (ICDs), accurate patient stratifi cation based on the future risk of arrhythmic events has become very relevant in ChD (3) .
A major therapeutic goal in the management of Chagas cardiomyopathy is prevention of sudden cardiac death.While ICD therapy is the standard treatment for secondary prevention of cardiac arrest, the strategy for primary prevention of cardiac arrest in Chagas cardiomyopathy is much more controversial.Although several clinical features have been assessed as possible risk factors for the development of fatal arrhythmias, the sensitivity and specifi city of any single test to predict fatal arrhythmias are limited.For example, left ventricular dysfunction is recognized as a strong general risk predictor, particularly for arrhythmic death in ChD (4) ; however, the mere presence of a depressed left ventricular ejection fraction (LVEF) is not sensitive or specifi c enough to stratify the risk of sudden death.Most patients with ChD that have an ICD for secondary prevention and thus have experienced a potentially fatal arrhythmic event have an LVEF >30%.

Electrocardiographic techniques
In the last few years, several new electrocardiographic methods have been used to predict mortality in ChD including measurement of the length of the QRS and QT intervals from a standard 12-lead ECG, which is a simple and inexpensive method of risk assessment in ChD.QT dispersion is associated with left ventricular (LV) systolic dysfunction, and both increased QT dispersion and QT interval are related to a higher risk of death in ChD patients (5) .Moreover, in another study performed in the same study sample, T-wave axis deviation was a strong and independent predictor of mortality risk.Furthermore, T-wave amplitude index, a marker of repolarization variability, is related to the risk of death in ChD, independent of other established risk factors (6) .The presence of late potentials on signal-averaged ECG, a marker of the presence of slow conduction regions, is related to a higher risk of death (7) , as is an increased dispersion of repolarization times in patients with ChD in both univariate and multivariate survival analyses (8) .Although these and other tests have demonstrated prognostic value for overall mortality, the prediction of malignant arrhythmias and sudden death is still challenging.

Imaging techniques
Echocardiography is pivotal in the assessment of cardiac function and prognosis of ChD (9) ; it has been used from the traditional measurement of ejection fraction and diastolic function to the more recent introduction of the quantitation of regional function with parameters such as strain derived by speckle tracking, focusing on the quantifi cation of regional myocardial timing and function.Global longitudinal strain has proved more accurate than LVEF in quantifying LV function, and it is known to possess prognostic impact (10) .Alterations in regional myocardial deformation can be quantifi ed by strain echocardiography, and these may represent electromechanical interactions.Tissue heterogeneity, leading to a dispersed myocardial contraction, is associated with the risk of malignant arrhythmic events.Recent studies have shown that mechanical dispersion of myocardial contractions is closely related to ventricular arrhythmias in several diseases, including myocardial infarction, arrhythmogenic right ventricular cardiomyopathy, and long QT syndrome (11) .
In a recent study, Barros et al. (data not published) used mechanical dispersion assessed by two-dimensional strain echocardiography in the evaluation of ChD patients with an ICD compared with ChD patients without an ICD.Mechanical dispersion was significantly different between the groups (<0.001), with high accuracy (cut-off, 57ms; sensitivity = 79%; specifi city = 74%; AUC = 0.83) for discriminating the ChD group (Figure 1).The use of myocardial dispersion by strain echocardiography could be an attractive tool in the decision making for the use of ICD as primary prevention for sudden cardiac death in ChD.
Cardiac magnetic resonance imaging (CMRI) with a delayed enhancement technique provides an excellent correlation with fi brosis, including the identifi cation of the ChD-related inflammatory process.Such findings support the hypothesis that CMRI can be an important tool to assess fi brosis in ChD.
Recent studies have demonstrated that CMRI improves the risk stratifi cation of patients with ChD and identifi es those more susceptible to ventricular tachycardia (VT).Mello et al (12) .showed that the identification of two or more contiguous segments of transmural DE is associated with greater probability of clinical VT (12) .Despite the progress in the prediction of malignant arrhythmias in ChD, practically none of these methodologies are used clinically to further subclassify individuals at risk of sudden cardiac death and help refi ne therapy.Whether the previously mentioned mechanical, electrical, and histological indices are correlated, additive, or merely provide redundant prognostic information needs to be evaluated in future adequately designed studies for reliable testing of the clinical utility of risk variables for the prediction of arrhythmic death.
Another principal uncertainty is derived from the progressive character of ChD, with the development of heart failure, LV remodeling, or other factors that could alter the electrophysiological arrhythmic substrate.Furthermore, the parameters used for stratifi cation also change with time, making the management more complex and diffi cult.

FIGURE 1 -
FIGURE 1 -Strain curves from a patient with Chagas disease (ChD) without an implantable cardioverter-defi brillator (ICD) (left panel) and a patient with ChD with an ICD (right panel).White horizontal arrows indicate time to peak strain, defi ned from onset of Q/R on ECG.Global longitudinal strain was calculated as the average of 16 left ventricular (LV) segments.Mechanical dispersion was defi ned as the standard deviation of the contraction duration of 16 LV segments.The ChD patient with an ICD shows more pronounced mechanical dispersion compared with the patient without an ICD.