Introduction
Inappropriate sinus tachycardia (IST) is a common cause of tachycardia in young adults. While generally benign, it can lead to debilitating symptoms such as dizziness, anxiety, and exercise intolerance, ultimately resulting in a significantly reduced quality of life. In addition to conservative measures such as endurance training and yoga, pharmacological therapy plays a central role in the treatment of IST. However, medical therapy is often insufficient or poorly tolerated due to side effects such as hypotension - particularly in younger, drug-sensitive patients.
Case Presentation
A 25-year-old female ICU nurse presented to our outpatient clinic with recurrent episodes of tachycardia, dizziness, and presyncope, significantly impairing her exercise tolerance and overall quality of life. The symptoms had been present for several years and occurred both at rest and during physical activity, often triggered by caffeine or alcohol. The patient was athletic with a BMI of 18.7. A Holter ECG showed a narrow-complex tachycardia with a P-wave morphology closely resembling sinus rhythm and heart rates reaching up to 110 bpm at rest and 200 bpm during exercise, both with typical warming-up and cooling-down phases. Ergometry revealed a heart rate of 200 bpm at just 100 Watts. Echocardiography was unremarkable for her age, and no secondary causes of sinus tachycardia were identified, leading to a diagnosis of IST.
Prior to presentation at our clinic, multiple pharmacologic treatments had already been attempted under the same presumptive diagnosis, including calcium channel blockers, flecainide, and beta-blocker monotherapy, all of which failed to adequately control the IST. Initial treatment with Ivabradine, even in combination with beta-blockers, was also ineffective and caused visual disturbances as side effects.
We then initiated therapy with a combination of Carvedilol and Flecainide, which successfully suppressed the tachycardia. However, within a few days, the patient developed symptomatic hypotension with systolic blood pressure dropping to 70 mmHg. Despite the effective rhythm control, the hypotension became a limiting factor. After thorough discussion with the patient, we decided to manage the hypotension rather than abandon the effective anti-arrhythmic therapy. We added the α1-agonist midodrine at a dose of 20 drops three times daily. This led to normalization of blood pressure and complete resolution of all symptoms. The patient has remained symptom-free for the past six months.
Discussion and Conclusion
This case highlights an alternative therapeutic strategy in a patient with initially treatment-refractory IST. Multiple pharmacologic approaches, including off-label combinations, failed to provide symptom relief, raising the consideration of sinus node ablation or modulation due to the patient’s high symptom burden. However, by choosing to accept the side effect of hypotension associated with an otherwise effective regimen and managing it with midodrine, invasive intervention was avoided.
Midodrine may thus represent a promising add-on therapy in IST patients where hypotension would otherwise necessitate discontinuation of an effective rhythm-control strategy.
