Imaging Evaluation

Abstract

Progress in the fields of diagnostic technique, surgical and interventional treatment, anesthesia, postoperative clinical management and general medical care fields has improved the outcome of patients operated upon for congenital diseases. Many of these adult patients are those operated on for ToF, and these patients frequently need re-intervention, mostly related to surgical remodeling of the right ventricle outflow tract (RVOT) such as residual stenosis or, more frequently, pulmonary regurgitation (PR). This condition particularly affects right ventricular function, which could be also impaired by other concomitant conditions such as peripheral pulmonary stenosis and increased pulmonary vascular resistance which worsen PR or any other associated defect, or acquired pulmonary or cardiac diseases. PR and RVOT changes are direct consequences of complete surgical correction of ToF with infundibulectomy and transannular patching; this may result in RVOT aneurysmal dilation and a large pulmonary annulus. This condition may be tolerated for several years, but, depending on its severity, it results in a progressive right ventricular dilation and dysfunction at certain ages. Long standing chronic right ventricular volume overload also affects the right ventricular inflow tract by tricuspid annulus dilation which results in different degrees of tricuspid regurgitation. This further worsens right ventricle dilatation and dysfunction, affecting also left ventricular filling and function. There are several causes of left ventricular dysfunction such as distortion of the interventricular septum which affects interventricular interaction, aortic dilation with aortic regurgitation, ventricular dissynchronicity and reduced left ventricular diastolic filling [1]. Furthermore, right ventricular dilation causes atrial and ventricular tachyarrhythmias, which are considered an important risk factor for sudden death in this type of patient [2]. Imaging examination in adult postoperative status with PR should address the assessment of several indicators of right ventricular function in order to indicate the most appropriate timing for pulmonary valve replacement (PVR). The answer to this question remains one of the most challenging and controversial points for a clinician. Several authors proposed MRI measurements of right ventricular volumes as a main indicator for PVR: an RV end-diastolic volume greater than 170 ml/m² or a RV end-systolic volume greater than 85 ml/m² have been proposed [3] as a cut off for reoperation to obtain substantial right ventricular normalization after surgery. Other authors considering even correlation between right ventricular volume, cardiac output and exercise test changes after PVR, proposed a relatively more aggressive PVR policy (end diastolic volume less than 150 mL/m², and this resulted in: normalization of right ventricular volumes, improvement in biventricular function, and submaximal exercise capacity [4]. MRI is considered the gold standard for measurement of RV [5] volume, but 2D and more recently 3D echocardiography in the hands of an experienced operator may provide a reliable volume measurement [6, 7] together with much other information that may be obtained in a comprehensive echocardiographic exam [8]. Nevertheless, timing for reoperation frequently remains a dilemma, especially considering the young age of most patients and the relative duration of the biological prosthesis implanted. In the decision of setting a measure of right ventricular volumes obtained by MRI or echocardiography should never be considered as a unique indicator, evaluation of a patient operated for ToF and who is a candidate for PVR should include also electrocardiogram (ECG) and Holter recording, thoracic radiography and, in selected patients, cardiac catheterization.