A 22-year-old woman is evaluated in the emergency department because of symptoms of prolonged palpitations. She complains of no associated chest discomfort, shortness of breath, or lightheadedness. The palpitations have occurred twice before, but they always stopped spontaneously after 5 minutes, and she cannot associate them with any triggers. The past health history is negative and she is not on any medications.On physical examination, the blood pressure is 110/70 mm Hg, heart rate is 160/min and regular. The heart and lung examinations are normal, and the ECG is shown in Figure below. The heart rate abruptly changes to 72/min after applying carotid sinus pressure. Which of the following is the most likely diagnosis?
A 22-year-old woman is evaluated in the emergency department because of symptoms of prolonged palpitations. She complains of no associated chest discomfort, shortness of breath, or lightheadedness. The palpitations have occurred twice before, but they always stopped spontaneously after 5 minutes, and she cannot associate them with any triggers. The past health history is negative and she is not on any medications.On physical examination, the blood pressure is 110/70 mm Hg, heart rate is 160/min and regular. The heart and lung examinations are normal, and the ECG is shown in Figure below. The heart rate abruptly changes to 72/min after applying carotid sinus pressure. Which of the following is the most likely diagnosis?
💡 Explanation
## **Core Concept**
The question tests the understanding of supraventricular tachycardias (SVTs), specifically focusing on the diagnosis and management of paroxysmal supraventricular tachycardia (PSVT). PSVTs are characterized by episodes of rapid heart rate that originate above the ventricles and are often associated with a narrow QRS complex on the electrocardiogram (ECG).
## **Why the Correct Answer is Right**
The correct answer, **. Atrioventricular Reentrant Tachycardia (AVRT)**, is likely because the patient's symptoms and ECG findings are consistent with AVRT. AVRT is a type of PSVT that involves a reentrant circuit within the atrioventricular (AV) node or between the atria and ventricles, often utilizing an accessory electrical pathway. The abrupt termination of the tachycardia with carotid sinus pressure, which increases vagal tone and slows AV nodal conduction, supports this diagnosis. The regular heart rate of 160/min and the lack of associated symptoms such as chest discomfort or shortness of breath are also consistent with AVRT.
## **Why Each Wrong Option is Incorrect**
- **Option A:** While **Atrioventricular Nodal Reentrant Tachycardia (AVNRT)** is another common cause of PSVT and can present similarly, it is less likely to be distinguished from AVRT based solely on the information given. However, AVNRT typically does not involve an accessory pathway.
- **Option B:** **Atrial Fibrillation with Rapid Ventricular Response** usually presents with an irregularly irregular heart rhythm, which does not match the regular rhythm described in the scenario.
- **Option C:** **Atrial Tachycardia** could present with a similar heart rate but often has P waves visible on the ECG that are not consistent with a typical sinus rhythm, and the response to carotid sinus pressure might differ.
## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that **vagal maneuvers**, such as carotid sinus pressure, can help terminate certain types of SVTs, including AVRT and AVNRT, by increasing parasympathetic tone and slowing conduction through the AV node. This is a useful diagnostic and therapeutic tool in the acute management of PSVT.