Multimodality Imaging in Athletes: Addressing the "Gray Zone"
A 26-year-old male cyclist with no significant medical history was referred to a cardiologist for an evaluation of dyspnea. His training regimen consisted of ten hours of cycling per week with several maximum intensity rides and longer weekend rides lasting approximately four to five hours each. He recently noticed that he was having difficulty maintaining his pace with his fellow cyclists and was concerned that his exercise performance was declining. While he endorsed feeling better during exercise, he stated that he noticed a rapid, regular heart rate with pinching, focal chest discomfort at night during rest. After an unrevealing physical exam, a 12-lead ECG was obtained (Figure 1). He subsequently completed 24-hour ambulatory ECG monitoring which revealed sinus rhythm and rare pre-ventricular contractions without associated symptoms. At a time of reported "palpitations," his rhythm was normal sinus at 79 beats per minute.
Figure 1: Baseline electrocardiogram
2-D transthoracic echocardiography was completed and reported normal left ventricular (LV) size (LVEDD 5.3cm) with LV systolic ejection fraction by Simpson's biplane method of 48% and normal LV diastolic filling pattern. Global longitudinal systolic strain (GLS) via 2D speckle tracking was suggestive of mildly reduced LV systolic function (GLS -16.9, Vendor GE). Right ventricular size and function were reported as normal and both atria were mildly dilated. Labs including a complete blood count, basic metabolic panel, cardiac biomarkers, thyroid function studies and iron studies were within normal limits. Acute phase reactants were collected and revealed a normal erythrocyte-sedimentation rate and mildly elevated C-reactive protein. A viral panel was obtained and showed elevated Coxsackie B and Echovirus titers. In addition, cardiac magnetic resonance imaging was completed (Figure 2).
Figure 2: Cardiac magnetic resonance imaging
The patient completed a maximal 19 minute and 20 second cardiopulmonary exercise test via a 25-watt bike ramp protocol and achieved a VO2 max of 53.6 ml/kg/min (132% predicted) consistent with excellent physical conditioning. His O2 pulse was within normal limits (125% predicted). His normal VE/VCO2 slope of 25 and normal PETCO2 were indicative of normal pulmonary perfusion and ventilation-perfusion matching during exercise. He demonstrated a normal chronotropic response with exercise, achieving a maximum heart rate of 188 beats per minute (97% maximum predicted heart rate) and had appropriate augmentation of his blood pressure with exercise (resting blood pressure 140/96 mmHg, peak blood pressure with exercise 200/71 mmHg). He remained asymptomatic and in sinus rhythm throughout the study without evidence of ischemia or sustained arrhythmias (Figure 3).
Figure 3: Cardiopulmonary exercise testing
Which of the following is the most likely diagnosis?