What is the initial workup for a 12-year-old female patient experiencing tachycardia with movement and dizziness?

Initial Workup for Tachycardia with Movement and Dizziness in a 12-Year-Old Female

The initial workup for a 12-year-old female with tachycardia during movement and dizziness should focus on orthostatic intolerance evaluation, including an active standing test to assess for Postural Orthostatic Tachycardia Syndrome (POTS), which is characterized by a heart rate increase ≥40 bpm within 10 minutes of standing in adolescents aged 12-19 years. 1

Initial Cardiovascular Assessment

• Obtain a 12-lead ECG to evaluate for cardiac conduction abnormalities and to establish a baseline cardiac rhythm 2, 1
• Perform an active standing test: measure heart rate and blood pressure while supine, then after standing for 10 minutes, looking specifically for a heart rate increase ≥40 bpm without significant blood pressure drop (diagnostic for POTS in adolescents) 1
• Document all associated symptoms during standing, including lightheadedness, palpitations, tremor, weakness, and visual disturbances 1
• Assess for classic orthostatic hypotension (drop in systolic BP ≥20 mmHg or diastolic BP ≥10 mmHg within 3 minutes of standing) 2
• Evaluate for delayed orthostatic hypotension by extending standing time beyond 3 minutes, as this can be missed with brief monitoring 1

Laboratory Testing

• Complete blood count to evaluate for anemia, which can cause tachycardia and dizziness 1
• Comprehensive metabolic panel to assess electrolytes, renal function, and glucose levels 1
• Thyroid function tests to rule out hyperthyroidism, which can present with tachycardia 1
• Iron studies, including ferritin, iron, and TIBC, to evaluate for iron deficiency 1

Additional Cardiovascular Evaluation

• Consider 24-hour Holter monitoring if symptoms suggest paroxysmal arrhythmia or if the initial evaluation is inconclusive 2, 1
• Echocardiogram should be performed to exclude structural heart disease, which is essential in the evaluation of patients with suspected tachyarrhythmias 2, 1
• Consider tilt-table testing if the active standing test is inconclusive but symptoms strongly suggest orthostatic intolerance 1

Differential Diagnosis Considerations

• Postural Orthostatic Tachycardia Syndrome (POTS): Heart rate increase ≥40 bpm in adolescents within 10 minutes of standing without significant BP drop 1
• Supraventricular tachycardia (SVT): Paroxysmal episodes with abrupt onset/offset, heart rate typically 150-250 bpm 2, 3
• Sinus tachycardia: Gradual onset/offset, often secondary to underlying conditions like fever, anemia, or dehydration 2
• Reflex syncope: Vasovagal episodes triggered by emotional stress, pain, or prolonged standing 2
• Anxiety-related tachycardia: Often misdiagnosed in patients with POTS due to overlapping hyperadrenergic symptoms 4

Important Clinical Considerations

• Don't dismiss orthostatic symptoms in adolescents as "just dehydration" or anxiety, as POTS is frequently misdiagnosed 1, 4
• Assess for common POTS comorbidities including chronic fatigue syndrome, recent infections, and joint hypermobility syndrome 1
• Evaluate the pattern of tachycardia - whether it's paroxysmal (sudden onset/offset) suggesting SVT, or gradual onset/offset suggesting sinus tachycardia 2
• Document if symptoms occur only with position changes (suggesting orthostatic intolerance) or with exertion (suggesting possible arrhythmia or structural heart disease) 2
• Consider rare causes such as ventricular tachycardia, which can present with dizziness during exercise even in patients without structural heart disease 5

This systematic approach ensures comprehensive evaluation of the most common and serious causes of tachycardia with movement and dizziness in adolescents, with particular attention to orthostatic intolerance syndromes that are common in this age group.