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Related Concept Videos

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Bradyarrhythmias are cardiac rhythm disorders characterized by a slower-than-normal heart rate, typically defined as fewer than 60 beats per minute. Some of which are discussed here:Sinus BradycardiaSinus bradycardia presents a heart rate lower than 60 beats per minute, with a regular rhythm originating from the SA node. The ECG typically shows normal P waves preceding each QRS complex, a normal PR interval (0.12 to 0.20 seconds), and a normal QRS duration (0.06 to 0.10 seconds).First-Degree AV...
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Depolarizing blockers act on skeletal muscle fibers' membranes and induce their depolarization. Most depolarizing blockers have two quaternary N+ atoms that bind the nicotinic acetylcholine receptors and cause neuromuscular blockade within minutes.
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Adrenergic stimulation generally impacts cardiac rate and rhythm. Specifically, stimulation of the β-adrenoceptors triggers an increase in intracellular calcium ion influx and pacemaker currents, which may cause arrhythmias. Catecholamines like adrenaline also demonstrate β2-adrenoceptor-mediated hypokalemia, impacting cardiac action potential and disrupting the normal cardiac rhythm. Class II antiarrhythmic drugs are β-adrenoceptor antagonists or β-blockers, which...
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Nondepolarizing neuromuscular blockers induce paralysis by competitively blocking nicotinic acetylcholine receptors at the muscle end plate. Examples include pancuronium, mivacurium, vecuronium, and rocuronium. These quaternary ammonium derivatives are administered intravenously, are poorly absorbed, and are excreted via the kidneys.
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The site of chemical communication between a motor neuron and a muscle fiber is called the neuromuscular junction (NMJ). The end of the motor neuron at the NMJ divides into a cluster of synaptic end bulbs. The cytoplasm of these bulbs consists of synaptic vesicles enclosing acetylcholine molecules, the principal neurotransmitter released at the NMJ. The region opposite the synaptic bulb that ends in the muscle fiber is called the motor end plate, which has acetylcholine receptors. Within the...
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Arrhythmia or dysrhythmia refers to an abnormal heart rhythm caused by a defect in the heart's conduction system. It can cause the heart to beat irregularly, too quickly, or too slowly, leading to symptoms like chest pain, shortness of breath, and fainting. Factors such as stress, caffeine, alcohol, nicotine, cocaine, certain drugs, congenital defects, diseases, and electrolyte abnormalities can trigger arrhythmias.
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Related Experiment Video

Updated: May 3, 2026

Benefits of Cardiac Resynchronization Therapy in an Asynchronous Heart Failure Model Induced by Left Bundle Branch Ablation and Rapid Pacing
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[Masquerading bundle branch block].

Piotr Kukla1, Adrian Baranchuk, Marek Jastrzębski

  • 1Department of Internal and Cardiology, Specialistic Hospital, Gorlice. kukla_piotr@poczta.onet.pl.

Kardiologia Polska
|January 29, 2014
PubMed
Summary

This case study details an atypical electrocardiogram (ECG) pattern in a patient with chemotherapy-induced cardiomyopathy. The findings highlight a rare form of masquerading bundle branch block, crucial for accurate cardiac diagnosis.

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Area of Science:

  • Cardiology
  • Electrophysiology
  • Medical Diagnostics

Background:

  • Chemotherapy-induced cardiomyopathy can lead to complex cardiac conditions.
  • Electrocardiograms (ECG) are vital for diagnosing heart abnormalities.
  • Bundle branch blocks (BBB) affect the heart's electrical conduction system.

Observation:

  • A 72-year-old female with a history of breast cancer and chemotherapy-induced cardiomyopathy presented with specific ECG findings.
  • The ECG revealed atrial fibrillation, left ventricular dysfunction, right bundle branch block (RBBB), and left anterior fascicular block (LAFB).
  • The patient exhibited an atypical masquerading bundle branch block, with absent S waves in lead I and precordial leads V5-V6.

Findings:

  • The observed ECG pattern combined features of RBBB and LAFB, a rare presentation known as masquerading bundle branch block.
  • This specific pattern, with absent S waves in lead I and precordial leads, can be mistaken for Left Bundle Branch Block (LBBB).
  • The atypical axis deviation and absence of S waves suggest underlying left ventricular hypertrophy or myocardial scarring/fibrosis.

Implications:

  • Accurate identification of masquerading bundle branch block is critical for appropriate patient management.
  • This ECG pattern underscores the importance of detailed analysis in patients with cardiac dysfunction and a history of cardiotoxic treatments.
  • Recognizing this rare variant can prevent misdiagnosis and guide further cardiac investigations and therapeutic strategies.