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Differential Diagnosis for M Shaped QRS in Lead 3

Single Most Likely Diagnosis

  • Right Bundle Branch Block (RBBB): This condition is characterized by a delay or blockage in the right bundle branch, leading to an abnormal QRS complex. The M shape in lead 3 can be indicative of RBBB due to the altered ventricular depolarization pattern.

Other Likely Diagnoses

  • Left Anterior Fascicular Block (LAFB): This condition involves a blockage in the anterior fascicle of the left bundle branch, which can also lead to an abnormal QRS complex. The M shape in lead 3 might be seen in LAFB due to the changed depolarization pattern of the left ventricle.
  • Wolff-Parkinson-White (WPW) Syndrome: WPW syndrome is a condition where an accessory electrical pathway between the atria and ventricles causes the heart to beat too quickly. The M shape in lead 3 could be a manifestation of the pre-excitation pattern seen in WPW.

Do Not Miss Diagnoses

  • Ventricular Tachycardia (VT): Although less common, VT can present with an M shaped QRS complex in lead 3, especially if the origin of the tachycardia is from the right ventricle. Missing VT could be fatal, making it a critical diagnosis not to overlook.
  • Hyperkalemia: Severe hyperkalemia can cause significant changes in the ECG, including widening of the QRS complex, which might appear as an M shape in certain leads. Hyperkalemia is a medical emergency that requires immediate attention.

Rare Diagnoses

  • Cardiac Sarcoidosis: This rare condition involves the infiltration of the heart by sarcoid granulomas, which can disrupt the normal electrical conduction of the heart, potentially leading to abnormal QRS complexes.
  • Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC): ARVC is a rare heart condition where the muscle in the right ventricle is replaced by fat and scar tissue, which can lead to abnormal heart rhythms and potentially an M shaped QRS complex in certain leads.

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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