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Related Concept Videos

Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers01:20

Antiarrhythmic Drugs: Class IV Agents as Calcium Channel Blockers

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Class IV antiarrhythmic drugs, such as verapamil and diltiazem, block calcium channels. They primarily affect the heart, slowing the conduction in calcium-dependent tissues like the SA and AV nodes. These drugs manage reentrant supraventricular tachycardia (SVT) and reduce ventricular rate in atrial flutter/fibrillation.
Verapamil, a calcium channel blocker, inhibits calcium movement across myocardial cell membranes and vascular smooth muscle. This results in the dilation of coronary and...
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Dysrhythmias IV: Characteristics of Bradyarrhythmias01:18

Dysrhythmias IV: Characteristics of Bradyarrhythmias

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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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Disturbances in Heart Rhythm01:29

Disturbances in Heart Rhythm

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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.
Arrhythmias are categorized by their speed, rhythm, and origin. A slow heart...
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Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers01:22

Antiarrhythmic Drugs: Class I Agents as Sodium Channel Blockers

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Class I antiarrhythmic drugs are used to treat various types of arrhythmias or irregular heart rhythms. These drugs block the sodium (Na+) channels in the cardiac cells, thereby affecting the movement of electrical impulses across the heart. Class I antiarrhythmic drugs are divided into three subgroups: Class IA, Class IB, and Class IC, each with distinct mechanisms of action and effects on the heart.
Class 1A Antiarrhythmic Drugs: These drugs work by moderately blocking sodium channels,...
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Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers01:12

Antiarrhythmic Drugs: Class III Agents as Potassium Channel Blockers

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Class III antiarrhythmic drugs are a group of medications that can prolong action potentials in the heart. They achieve this by blocking potassium channels or enhancing inward currents from sodium channels. However, these drugs have a unique property of "reverse use-dependence," which is most pronounced at slower heart rates and can lead to torsades de pointes—a specific type of arrhythmia. However, it is essential to note that excessive QT interval prolongation—a measure of...
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Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers01:24

Antiarrhythmic Drugs: Class II Agents as β-Adrenergic Blockers

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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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Updated: Nov 21, 2025

Isolation of Human Atrial Myocytes for Simultaneous Measurements of Ca2+ Transients and Membrane Currents
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Reversible complete heart block due to hypercalcaemia.

Venkatakrishnan Ramakumar1, Shyam S Kothari2, Sandeep Seth1

  • 1Department of Cardiology, All India Institute of Medical Sciences, New Delhi, India.

BMJ Case Reports
|January 19, 2021
PubMed
Summary
This summary is machine-generated.

Severe hypercalcemia, a condition of high calcium levels, can cause complete heart block. This heart rhythm issue resolved after correcting the calcium levels and removing a parathyroid adenoma.

Keywords:
arrhythmiascalcium and bonecardiovascular medicinepacing and electrophysiology

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Area of Science:

  • Cardiology
  • Endocrinology
  • Internal Medicine

Background:

  • Syncope can be caused by various cardiac arrhythmias.
  • Complete heart block is a serious cardiac condition requiring prompt diagnosis and management.

Observation:

  • A 65-year-old woman presented with syncope and ECG findings of complete heart block with a narrow QRS escape rhythm and normal QT interval.
  • Laboratory investigations revealed severe hypercalcemia and elevated parathormone levels.

Findings:

  • The patient's complete heart block resolved upon correction of severe hypercalcemia.
  • A parathyroid adenoma was identified as the cause of hypercalcemia.

Implications:

  • This case highlights that severe hypercalcemia can induce reversible complete heart block.
  • The absence of QT interval shortening in this case suggests a distinct mechanism compared to other causes of heart block.
  • Endocrine disorders, such as parathyroid adenomas, should be considered in the differential diagnosis of unexplained cardiac conduction abnormalities.