The Question is from neet-zoology body-fluids-and-circulation , and it was created by the author Mr. BALACHANDRA.N

Question

An ECG shows a regular, narrow-complex tachycardia with a rate of 170 bpm.  P waves are difficult to discern.  Carotid sinus massage terminates the tachycardia. Which is the MOST likely diagnosis?

Mr. BALACHANDRA.N · Accepted Answer

## CORE INFORMATION
✓ **Answer**: C
## CONCEPT FRAMEWORK
 **Primary Concept**: Electrocardiogram (ECG) interpretation and supraventricular tachycardias.
 **Related Topics**: Cardiac arrhythmias, carotid sinus massage, differential diagnosis of tachycardias.
 **Prerequisites**: Understanding of ECG waveforms (P waves, QRS complexes), heart rate calculation, and the mechanism of carotid sinus massage.
## SOLUTION PATHWAY
**Given Information**:
  * Regular, narrow-complex tachycardia:  Indicates the origin of the tachycardia is above the ventricles (supraventricular).
  * Rate of 170 bpm:  A significantly elevated heart rate.
  * P waves are difficult to discern:  Suggests that atrial activity is rapid and/or obscured by the ventricular activity.
  * Carotid sinus massage terminates the tachycardia: This maneuver increases vagal tone, slowing conduction through the AV node.  It is effective in terminating many supraventricular tachycardias.
**Method & Steps**:
 1. Analyze the ECG characteristics: The narrow QRS complex rules out ventricular tachycardia (wide QRS complexes are characteristic of ventricular tachycardia).
  Reasoning: Ventricular tachycardia originates in the ventricles, leading to wide QRS complexes.
  Formula/Rule: None directly applicable, but understanding ECG morphology is crucial.
 2. Consider the effect of carotid sinus massage: The successful termination of the tachycardia by carotid sinus massage strongly suggests a supraventricular origin, as this maneuver primarily affects the AV node conduction.
  Working:  Carotid sinus massage increases parasympathetic activity, slowing AV nodal conduction. This is effective in many SVTs but not in ventricular tachycardias.
  Key Point: The response to carotid sinus massage is a key differentiating factor.
 3. Differential diagnosis:  Given the regular rhythm and response to carotid sinus massage, atrial fibrillation (irregular rhythm) and sinus tachycardia (usually less than 100 bpm) are less likely.
  Result: Supraventricular tachycardia (SVT) is the most likely diagnosis.
  Verification: All the given information supports the diagnosis of SVT.
 ## OPTION ANALYSIS
A :x: Ventricular tachycardia is incorrect because the QRS complex is narrow, not wide.
B :x: Atrial fibrillation is incorrect because it is characterized by an irregular rhythm, not a regular one.
C ✓: Supraventricular tachycardia (SVT) is correct because it aligns with all the ECG findings and the response to carotid sinus massage.
D :x: Sinus tachycardia is incorrect because the heart rate is excessively high (170 bpm) for sinus tachycardia.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Misinterpreting the QRS complex width:  A wide QRS complex suggests a ventricular origin; a narrow complex suggests a supraventricular origin.
  2.Overlooking the significance of carotid sinus massage:  A positive response strongly suggests supraventricular tachycardia.
 **Quick Tips**:
  1.Remember the key characteristics of different tachycardias (e.g., regular vs. irregular rhythm, narrow vs. wide QRS complex).
  2.Use a systematic approach to ECG interpretation, considering all available information.

Mr. BALACHANDRA.N · Answer

Ventricular tachycardia

Mr. BALACHANDRA.N · Answer

Atrial fibrillation

Mr. BALACHANDRA.N · Answer

The correct Option is "Supraventricular tachycardia (SVT)"

Mr. BALACHANDRA.N · Answer

Sinus tachycardia

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