Home Economics American Trypanosomiasis Chagas Disease, Second Edition: One Hundred Years of Research
The cardiac form is the most serious and frequent manifestation of chronic Chagas disease. It develops in 20—30% of individuals and manifests as three major syndromes that may coexist in the same patient: arrhythmic, heart failure, and thromboembolism (systemic and pulmonary).19 Clinical presentation varies widely according to the extent of myocardial damage.
Arrhythmias are very common and of different types, frequently in association (Fig. 28.5), and cause palpitations, presyncope, syncope, and Stokes—Adams syndrome; sometimes arrhythmias are asymptomatic.
Frequent, complex, ventricular premature beats, including couplets and runs of nonsustained ventricular tachycardia, are a common finding on 24-h Holter monitoring or stress testing (Fig. 28.6).
They correlate with the severity of ventricular dysfunction, but can also occur in patients with relatively well-preserved ventricular function. Episodes of nonsustained ventricular tachycardia are seen in approximately 40% of patients with mild wall motion abnormalities and in virtually all patients with heart failure, an incidence that is higher than that observed in other cardiomyopathies.20 Sustained ventricular tachycardia is another hallmark of the disease. This life-threatening arrhythmia can be reproduced during programmed ventricular stimulation in approximately 85% of patients and seems to result from an intramyocardial or subepicardial re-entry circuit usually located at the inferior—posterior—lateral wall of the left ventricle.21,22
Heart failure is often a late manifestation of Chagas heart disease. It is usually biventricular with a predominance of right-sided failure (peripheral edema, hepatomegaly, and ascites more prominent than pulmonary congestion) at advanced stages. Nocturnal paroxysmal dyspnea, cardiac asthma, and acute pulmonary edema are all rare. Gallop rhythm is infrequent. Once cardiomegaly appears, a systolic murmur of functional mitral or tricuspid regurgitation may be heard. Isolated left heart failure can be seen in the early stages of cardiac decompensa- tion.23,24 Heart failure of chagasic etiology is associated with higher mortality than is heart failure from other causes.25 Systemic and pulmonary embolisms arising from mural thrombi in the cardiac chambers are quite frequent.26 Clinically, the brain is by far the most frequently recognized site of embolisms (followed by
Figure 28.5 Associated arrhythmias in patients with Chagas heart disease (24-h Hotter monitoring). (A) Sinus pauses and nonsustained ventricular tachycardia; (B) second degree atrioventricular block (Mobitz 2) and sinus pause of 15.0 s of duration (during sleep).
Figure 28.6 Frequent episodes of nonsustained ventricular tachycardia on stress testing (A) and on 24-h Holter monitoring (B) in patients with Chagas heart disease.
limbs and lungs), but at necropsy, embolisms are found more frequently in the lungs, kidneys, and spleen. Chagas disease is an independent risk factor for stroke in endemic areas.27
Sudden death is the main cause of death in patients with Chagas heart disease, accounting for nearly two-thirds of all deaths, followed by refractory heart failure (25—30%) and thromboembolism (10—15%).28 Sudden cardiac death can occur even in patients who were previously asymptomatic. It is usually associated with ventricular tachycardia and fibrillation or, more rarely, with complete atrioventricular block or sinus node dysfunction. Leading causes of death vary depending on the stage of disease, with a clear predominance of sudden death at early stages, and a slight predominance of death from pump failure at advanced stages.
Electrocardiographic alterations are varied, but the most frequent and important are ventricular premature beats (monomorphic or polymorphic, isolated or in pairs), complete right bundle branch block (CRBBB), left anterior fascicular block, primary ST-T changes, Q waves, different degrees of atrioventricular block, manifestations of sinus node dysfunction (sinus bradycardia, sinoatrial block, and sinus arrest), atrial fibrillation, and nonsustained or sustained ventricular tachycardia. All these alterations may be isolated or associated. A frequent association is CRBBB and left anterior fascicular block, and when this occurs in an endemic area, it strongly suggests chronic Chagas heart disease (Fig. 28.7).
Figure 28.7 ECG of a patient with Chagas heart disease showing the three most typical alterations: right bundle branch block, left anterior fascicular block, and ventricular extrasystole.
On radiological examinations, the cardiac size is generally normal in the initial phase of the cardiopathy and even when important electrocardiographic changes are present. The cardiac size may be slightly, moderately, or severely increased, in all chambers (Fig. 28.8). In nearly half of the cases with heart failure, the manifestations of pulmonary congestion are poor or even absent.
The echodopplercardiogram may be abnormal even in patients with a normal ECG and normal chest radiograph. Echo shows wall motion abnormalities in two main areas of the left ventricle: the apex and the posterior—inferior wall. The most characteristic findings are apical aneurysms (with or without thrombi) (Fig. 28.9) and akinesia or hypokinesia of the posterior wall of the left ventricle (with preservation of the atrioventricular septum).
Ambulatory ECG monitoring (Holter system) is an excellent method for investigating patients with Chagas heart disease.29—31 It may be used to identify complex ventricular arrhythmias, evaluate antiarrhythmic therapy, diagnose transitory arrhythmias, identify the association of tachyarrhythmias with bradyarrhythmias, evaluate people for job activities, and establish whether an artificial pacemaker is working properly. It is performed routinely for a 24-h period. In some cases a special device (event recorder) is used that registers ECG activity for several days.
Figure 28.8 Chest radiography of four patients with Chagas heart disease.
(A) Normal; (B) mild cardiomegaly; (C) moderate cardiomegaly; and (D) severe cardiomegaly without pulmonary congestion.
Figure 28.9 Two-dimensional echocardiogram showing left ventricular apical aneurysm with (arrow) and without thrombus.
The exercise testing evaluates the functional capacity of the patient, qualifies and quantifies ventricular premature beats, and may verify the efficacy of antiarrhythmic drugs.
Intracardiac electrophysiological studies evaluate the sinus node function, identify the location of atrioventricular and intraventricular blocks precisely, and investigate the inducibility of ventricular tachyarrhythmias, as well as their place of origin. It is of great value in the evaluation of presyncope and syncope of unknown origin, in indicating the need for an artificial pacemaker, as well as evaluating alternative methods of treatment of sustained ventricular tachycardia (e.g., catheter ablation). Because of its invasive nature, it should be performed only in selected patients or after all other noninvasive methods have been tried, such as Holter monitoring and exercise testing.
More recently, cardiac magnetic resonance has become an important tool in the assessment of cardiac function and myocardial structure. Not only segmental contractility, ventricular aneurysms, intracavitary thrombus, and left and right ventricular ejection fraction and volumes can be well defined, but also myocardial perfusion at rest and under stress are precisely determined. In addition, the myocardial areas of necrosis and/or fibrosis can be analyzed noninvasively and related to clinical aspects of Chagas cardiomyopathy, such as severe ventricular arrhythmias, symptoms of heart failure, sudden death, and other major events.32
Chagas heart disease can be divided schematically into four stages33 (Table 28.2).
In stage I, patients are usually symptom free and show mild and nonspecific ECG alterations. Left ventricular systolic function is preserved, but diastolic abnormalities may be found. Complex ventricular arrhythmias on 24-h Holter monitoring are rare. In stage II, manifestations include more specific conduction abnormalities, most frequently right bundle branch block, left anterior fascicular block (or both), complex ventricular arrhythmias, and segmental left ventricular wall motion abnormalities. Manifestations of later stages (III and IV)
Table 28.2 Stages of chronic Chagas heart disease
are: (1) sinus node dysfunction, usually leading to severe bradycardia; (2) high-degree heart block; (3) pathologic Q waves, low QRS voltage, and atrial fibrillation, compatible with extensive areas of myocardial fibrosis; (4) pulmonary and systemic thromboembolic phenomena due to thrombus formation in the dilated cardiac chambers or aneurysm; (5) cardiomegaly; and (6) progressive dilated cardiomyopathy with marked impairment of systolic function and congestive heart failure.
Improved understanding of prognostic factors in Chagas heart disease has helped clinicians to identify patients’ risk, choose appropriate treatment, and direct patient counseling. Some of us used a rigorous multivariate analysis to develop a risk score for mortality prediction in 424 outpatients from a regional Brazilian cohort and the score has been validated34,35 successfully in two external cohorts. Several demographic, clinical, and noninvasive variables were tested, and six were identified as independent predictors of mortality and were assigned points according to the strength of their statistical association with the outcome. From addition of the points to provide the risk score, patients can be classified into groups of low, intermediate, and high risk (Fig. 28.10).
Subsequently, two systematic reviews5,36 integrated the results of all previous studies in which multivariable regression models of prognosis were used and a clearly defined outcome (all-cause mortality, sudden cardiac death, or cardiovascular death) was analyzed. According to these reviews, the strongest and most consistent predictors of mortality are New York Heart Association (NYHA)
Figure 28.10 Prognostic factors in Chagas heart disease. Rassi score for prediction of total mortality. Echo, echocardiogram; NYHA, New York Heart Association; WMA, wall motion abnormality.
functional class III or IV, cardiomegaly on chest radiography, impaired left ventricular systolic function on echocardiogram or cineventriculography, and nonsustained ventricular tachycardia on 24-h Holter monitoring. On the basis of these findings, a risk stratification model for mortality, which can assist treatment in patients with Chagas heart disease, is proposed in Table 28.3.
With the exception of some peculiarities, the general principles that guide the symptomatic treatment of chronic Chagas heart disease are the same as those established for heart disease of other causes. Bradyarrhythmias are treated with pacemaker implantation. As a general rule, a pacemaker is indicated for all patients with symptomatic bradyarrhythmias or for those at high risk of complete atrioventricular block. The electrode should be placed in the subtricuspid zone37 avoiding the apex of the right ventricle, which may be thin, fibrotic, and contain thrombus.
Table 28.3 Stratification of risk of death associated with Chagas heart disease and recommended therapy
ACE, angiotensin-converting enzyme; echo, echocardiogram; ICD, implantable cardioverter-defibrillator; LV, left ventricular; NYHA, New York Heart Association; VT, ventricular tachycardia.
aNearly 100% of patients with Chagas heart disease in NYHA class III or IV also have LV systolic dysfunction on echo and nonsustained VT on 24-h Holter monitoring. bIf clinically tolerated. cFor selected patients.
Figure 28.11 (A) 24-h Holter monitoring in a patient with Chagas heart disease after pacemaker implantation showing (B and C) episodes of nonsustained ventricular tachycardia.
However, the management of rhythm disorders does not end with the implant of a pacemaker. Ventricular arrhythmias should also be promptly searched in patients with a pacemaker using the 24-h Holter monitoring and/or an exercise testing (Fig. 28.11), and treated accordingly.20
Ventricular arrhythmias are treated mainly with amiodarone; sotalol and beta blockers are second choice drugs. Propafenone and mexiletine have been used in some symptomatic patients with normal ventricular function based exclusively on their antiectopic activity. Quinidine, procainamide, and disopiramide do not have adequate antiarrhythmic activity; nevertheless, the use of procainamide when given intravenously for the treatment of paroxysmal ventricular tachycardia is highly effective. Monomorphic sustained ventricular tachycardia may also be amenable to percutaneous endocardial or pericardial ablation using catheter-delivered radiofrequency or cumulative high-energy fulguration in selected patients with mappable arrhythmia. The use of implantable cardioverter-defibrillators in patients with Chagas heart disease is hampered by the lack of controlled data to establish precise indications and efficacy38 as well as by socioeconomic limitations. A Brazilian randomized trial (CHAGASICS) is currently recruiting patients for a comparison of amiodarone versus the implantable cardioverter-defibrillator for primary prevention of death in patients with nonsustained ventricular tachycardia and a Rassi score of 10 or more points.39 For secondary prevention of sudden cardiac arrest or sustained ventricular arrhythmias, the implantable cardioverter-defibrillator is usually recommended, especially for patients with an ejection fraction less than 35%. When cardiac failure is present, it may be necessary to use higher doses of diuretics; angiotensin-converting enzyme inhibitors, espironolactone, and digoxin are also commonly used, and in special situations, betablockers are used.33 In some individuals, such as those with intractable cardiac failure following optimized treatment, a cardiac transplant is necessary; in this situation, the patient should usually receive specific treatment before or shortly after the surgical procedure. Palliative
procedures, such as dynamic cardiomyoplasty and partial left ventriculectomy, are contraindicated because of unsatisfactory results. Cardiac resynchronization is another form of treatment for heart failure, and is mostly for patients with left bundle branch block. Remarkably few data support its use in patients with right bundle branch block, which is much more common in patients with Chagas heart disease. The potential benefit of transplantation of bone marrow cells for treatment of Chagas heart failure was assessed in a multicenter randomized controlled trial sponsored by the Brazilian Health Ministry (MiHeart study), but it failed to show additional benefits over standard therapy in patients with severe heart failure.40
Because of the high occurrence of thromboembolic phenomena in Chagas heart disease, oral anticoagulants are recommended for patients with atrial fibrillation, previous embolic episodes, and apical aneurysm with thrombus. If poor social and economic factors limit the implementation of anticoagulant therapy, because of the increased risk of bleeding, the use of acetylsalicylic acid is considered a reasonable alternative.
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