INTRODUCTION

Chagas disease is still endemic in Latin America, in which more than 6 million people are infected by the Trypansosoma cruzi, the protozoan agent of the disease. T. cruzi is usually transmitted to human beings living in the countryside through the feces of kissing bugs Triatoma infestans, Rhodnius prolixus, and Triatoma dimidiate. Other, less common forms for disease diffusion is through blood transfusion, oral transmission, laboratory contamination, organ transplantation, and congenital transmission.

Chagas disease has been diffused throughout the world due to migration of contaminated people. At present, it is estimated there are 400,000 infected persons living in nonendemic countries, mainly in the United States and Europe. Since Chagas heart disease is an emerging problem in these countries, their cardiologists must be aware to recognize patients with Chagas cardiomyopathy, the most common and fatal complication of this disease that has its complete manifestation around 20 to 30 years after the patient has been infected.¹

CARDIAC ARRHYTHMIAS AND SUDDEN DEATH IN CHRONIC CHAGAS HEART DISEASE

Cardiac arrhythmias are very common findings in patients with Chagas cardiomyopathy, and ventricular arrhythmias are the leading cause of sudden cardiac death (SCD) in such patients.^2–4 Their prevalence and complexity are associated with progression and extension of the myocardial disease.^5,6

The sinus node dysfunction is a common cause of chronotropic deficit in patients with Chagas cardiomyopathy. It may be an expression of extrinsic autonomic denervation or due to an intrinsic nodal dysfunction secondary to myocardial damage.^3,7 Basic studies have suggested an important relationship between anti-β-adrenergic and anti-M2-cholinergic receptor antibodies and their biochemical effects also as a cause of the sinus node dysfunction in patients with Chagas disease.^8,9 Patients with symptomatic sinus node dysfunction due to Chagas disease were generally younger when compared to other cardiomyopathies¹⁰ and presented a clinical benefit when receiving permanent pacemakers to adjust their heart rate based on dynamic sensors.^11,12

Intra-atrial conduction disturbances are also common expressions of atrial myocardial damage. As a consequence, atrial fibrillation and flutter are frequently observed in patients with Chagas cardiomyopathy with prevalence increasing with aging and advanced stages of the disease.^2,13,14 A recent meta-analysis reviewing 30 studies and involving a total of 17238 patients, of whom 6840 (40%) had Chagas disease, showed that although atrial fibrillation was more prevalent in patients with Chagas disease, there was no difference when compared to patients with cardiomyopathy.¹⁵

Right bundle branch block (RBBB) is the most common conduction abnormality in Chagas disease, occurring in up to 40% of patients and it is frequently associated with left anterior hemiblock.^2,6,10,15 In the largest series, isolated RBBB occurred in 22.7% (adjusted OR: 10.73) and associated with left anterior hemiblock in 13.74% (adjusted OR: 12.09). Left bundle branch block (LBBB) is by far less common, occurring in up to 3%. Conduction system abnormalities can lead to AV block and syncope, the main cause for a permanent pacemaker implantation in such patients. However, sustained ventricular tachycardia (VT) has been reported as the main cause of recurrent syncope and bundle branch block.¹⁶ In those cases, electrophysiology study has been recommended for diagnosis clarification, especially when noninvasive methods fail in determining the cause.17,18

Premature ventricular contractions (PVCs) are frequent, and typically present multiple morphologies. The frequency and complexity of ventricular arrhythmias increase with disease progression^5,6 and are aggravated by adrenergic stimulation during physical activity,¹⁹ implying an enhanced risk of cardiac sudden death among young Chagasic patients, which is sometimes the first manifestation of the illness.^20,21

Nonsustained ventricular tachycardia (NSVT) has been recognized as an independent risk factor for death.⁴ Its identification on Holter monitoring was associated with a 2.15-fold increased risk of mortality, which raised to 15.1-fold when associated with important LV dysfunction. It has been estimated that SCD is responsible for 55% to 65% of deaths in patients with Chagas disease and that approximately 90% of the events are caused by ventricular arrhythmias. However, there are no randomized studies supporting the primary or secondary prevention in patients with Chagas disease. Thus, most clinical management recommendations for Chagasic patients with ventricular arrhythmias have been based on retrospective studies conducted by tertiary centers following patients with Chagas disease or based on randomized trials conducted in other non-Chagas cardiomyopathies.^17,18 Currently, a randomized trial is ongoing comparing amiodarone or implanted cardioverter-defibrillator (ICD) for primary prevention of patients with Chagas disease and in high risk for SCD.²²

IMAGING IN CHAGAS DISEASE

Cardiac MRI is the most important imaging method for managing patients with structural heart disease and VT, and in Chagas disease it is similarly valuable. The extension of fibrosis on MRI is related to the occurrence of VT. In one series, patients with VT had more fibrosis (25.4 ± 9.8%) compared to patients without VT (16 ± 12.3%) and indeterminate form (0.9 ± 2.3%; P ≤ 0.001).²³ In another series, myocardial fibrosis was associated with a median follow-up of 5.05 years, 44.6% of the patients with SCD, heart transplantation, ICD therapies, or aborted SCD had myocardial fibrosis associated with the primary outcome (adjusted hazard ratio: 1.031; 95% CI: 1.013 to 1.049; P = 0.001). Those events occurred in 44.6% of the patients in a follow-up of 5.05 years. Additionally, fibrosis of ≥ 12.3 g was also independently correlated to a worse outcome; by comparison, patients with no fibrosis had no major events in follow-up.²⁴ In another observation, patients with two or more contiguous segments of transmural fibrosis presented VT more frequently (RR 4.1; P = 0.04) and the distribution of fibrosis in patients was predominantly inferior, lateral, and basal in patients with VT and predominantly apical in patients without VT.²⁵

In a series of 81 patients with Chagas disease in the United States, mostly from El Salvador and Mexico,²⁶ in which MRI with late gadolinium enhancement (LGE) was performed, the pattern of the scar was predominantly transmural (56%, 65/117 segments) and mid-wall (30%, 35/117 segments). In contrast, the subendocardial pattern was uncommon (14%, 16/117 segments), and the subepicardial pattern was less common (< 1%, 1/117 segments). In another series, the authors identified epicardial only scar in 12.3% of the segments, mid-wall in 34.6%, and endocardial or transmural in 53.1%.

In our center, we use cardiac MRI and CT to identify presence, location, and size of LV aneurysms and scar (Figure 30.1). The use of automatic analysis tools of an MRI 3D LGE acquisition (ADAS Software, Galgo Medical SL, Barcelona, Spain) highlights the scar distribution and identifies the potentials conducting channels of VT. Another useful tool is the analysis of wall thickness on cardiac CT, because usually the abnormal potentials are in areas of wall thickness of less than 5 mm.²⁷

Unfortunately, the etiologic treatment has not been effective in the chronic phase of the disease.28 Therefore, the management of patients is directed to control Chagas disease consequences. Amiodarone has been traditionally the most commonly antiarrhythmic drug recommended to treat patients with recurrent sustained VT and Chagas cardiomyopathy.^17,18 In a series of 35 patients in the pre-ICD era, a mean dose of 356 ± 125 mg/day, suppressed VT recurrence in 44% of the patients in 36 months. In patients with ejection fraction (EF) ≤ 30%, the recurrence rate was 100%, but in patients with EF > 30%, only 30% presented VT recurrence.²⁹ In another series that included 115 patients with sustained or symptomatic NSVT and a mean EF of 49 ± 14%, patients who still presented inducibility of unstable VT using amiodarone presented a significantly higher mortality rate (69%) compared with patients that amiodarone use resulted in tolerated VT (26%) and non-inducibility of VT (26%) in a mean follow-up of 52 ± 32 months.³⁰

Cohort studies involving patients with sustained Chagas heart disease and sustained VT revealed 5% to 11.9% of annual mortality, with SCD representing 61% to 78% of the cases, mostly with important ventricular systolic dysfunction.^29,30

ICD Implantation

The ICD has been recommended to patients with sustained VT and ventricular dysfunction.^32–39 However, patients with Chagas cardiomyopathy had more ICD shocks compared to patients with coronary heart disease.^40,41 One series of 76 patients in the post-ICD group that were compared to a historical control group of 28 patients treated with amiodarone alone. The mean ejection fraction was 39 ± 12% in the ICD group and 41 ± 10% in the control group. An ejection fraction higher than 40% and the use of ICD were independently associated to a lower mortality. Patients in the control group, using amiodarone only, presented a death rate of 11% per year, where ICD patients presented 4.7% per year.38 In another series of 90 patients with ICD and a mean ejection fraction of 47 ± 13%, 71% presented ventricular arrhythmias in a mean follow-up of 756 ± 581 days, where 34% of the patients died in the follow-up, most due to pump failure. More than 4 shocks per month was independently associated with a higher mortality.³³ A meta-analysis including 115 patients in the amiodarone and 483 in the ICD group showed a similar mortality in both groups (9.6% and 9.7% per year, respectively).⁴²

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