Supraventricular Tachycardias

Supraventricular tachycardias are related disorders in which the elevation in heart rate is driven by pathophysiology in the atria. This group falls under the larger umbrella of tachyarrhythmias and includes paroxysmal supraventricular tachycardias (PSVTs), ventricular pre-excitation syndromes (i.e. Wolff-Parkinson-White syndrome), atrial flutter Atrial flutter Atrial flutter is a regular supraventricular tachycardia characterized by an atrial heart rate between 240/min and 340/min (typically 300/min), atrioventricular (AV) node conduction block, and a "sawtooth" pattern on an electrocardiogram (ECG). Atrial Flutter, multifocal atrial tachycardia, and atrial fibrillation Atrial fibrillation Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation. Sinus tachycardia (> 100/min) is not a pathologic arrhythmia. The diagnosis of these conditions can be made using electrocardiogram Electrocardiogram An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) ( ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG)), and treatment differs depending on the condition.

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Sinus Tachycardia

Etiology

  • Normal physiological response to exercise
  • Normal physiological response to a decrease in vagal tone (reflex tachycardia)
  • Sympathetic stimulation in pathological conditions ( fever Fever Fever is defined as a measured body temperature of at least 38°C (100.4°F). Fever is caused by circulating endogenous and/or exogenous pyrogens that increase levels of prostaglandin E2 in the hypothalamus. Fever is commonly associated with chills, rigors, sweating, and flushing of the skin. Fever, pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain, hyperthyroidism Hyperthyroidism Thyrotoxicosis refers to the classic physiologic manifestations of excess thyroid hormones and is not synonymous with hyperthyroidism, which is caused by sustained overproduction and release of T3 and/or T4. Graves' disease is the most common cause of primary hyperthyroidism, followed by toxic multinodular goiter and toxic adenoma. Thyrotoxicosis and Hyperthyroidism, hypovolemia, sepsis Sepsis Organ dysfunction resulting from a dysregulated systemic host response to infection separates sepsis from uncomplicated infection. The etiology is mainly bacterial and pneumonia is the most common known source. Patients commonly present with fever, tachycardia, tachypnea, hypotension, and/or altered mentation. Sepsis and Septic Shock, anemia Anemia Anemia is a condition in which individuals have low Hb levels, which can arise from various causes. Anemia is accompanied by a reduced number of RBCs and may manifest with fatigue, shortness of breath, pallor, and weakness. Subtypes are classified by the size of RBCs, chronicity, and etiology. Anemia: Overview, pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism, myocardial infarction Myocardial infarction MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction)
  • Exposure to stimulants Stimulants Stimulants are used by the general public to increase alertness and energy, decrease fatigue, and promote mental focus. Stimulants have medical uses for individuals with ADHD and sleep disorders, and are also used in combination with analgesics in pain management. Stimulants (nicotine, caffeine, amphetamines), anticholinergic drugs Anticholinergic drugs Anticholinergic drugs block the effect of the neurotransmitter acetylcholine at the muscarinic receptors in the central and peripheral nervous systems. Anticholinergic agents inhibit the parasympathetic nervous system, resulting in effects on the smooth muscle in the respiratory tract, vascular system, urinary tract, GI tract, and pupils of the eyes. Anticholinergic Drugs, beta-blocker medication withdrawal, illicit drugs (cocaine)

Clinical presentation

  • Palpitations
  • Postural orthostasis: fatigue, lightheadedness, exercise intolerance

Diagnosis

  • Heart rate > 100/min with normal P waves and QRS complexes observed via electrocardiogram Electrocardiogram An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) ( ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG))
  • The rate of impulses arising from the sinoatrial node is elevated.
  • Sinus tachycardia is typically regular, between 100/min and 180/min.
  • Determine underlying cause:
    • Volume depletion versus infection versus other medical conditions 
    • Via CBC, WBC, thyroid-stimulating hormone (TSH), angiography, urine drug test, etc.
Sinus tachycardia

Sinus tachycardia

Image: “Sinus tachycardia” by Faculty of Medicine, Zagazig University, Zagazig City, Egypt. License: CC BY 4.0

Treatment

  • Reverse the underlying cause
  • If reversible causes have been excluded, consider beta-blockers, then ivabradine, then catheter ablation.

Paroxysmal Supraventricular Tachycardias (PSVTs)

Etiology

  • Presents in young adulthood
  • Prevalence is similar in men and women and increases progressively with age.
  • 60% of PSVT cases are due to atrioventricular nodal reentry tachycardia (AVNRT):
    • Two different electrical pathways in the atrioventricular (AV) node form a loop that continuously conducts impulses leading to tachycardia.
    • The 2 pathways form a “fast” and “slow” pathway:
      • Anterograde conduction along the slow pathway 
      • Retrograde conduction along the fast pathway
  • 30% of PSVT cases are due to atrioventricular reciprocating tachycardia (AVRT).
    • The re-entry loop is formed by a normal AV node.
    • Abnormal presence of an accessory conduction pathway between the atria and the ventricles
    • Typified by Wolff-Parkinson-White (WPW) syndrome
  • 10% of PSVT cases are due to atrial tachycardia (AT) and sinoatrial nodal reentrant tachycardia (SANRT).

Clinical presentation

  • Palpitations
  • Syncope Syncope Syncope is a short-term loss of consciousness and loss of postural stability followed by spontaneous return of consciousness to the previous neurologic baseline without the need for resuscitation. The condition is caused by transient interruption of cerebral blood flow that may be benign or related to a underlying life-threatening condition. Syncope or presyncope
  • Lightheadedness or dizziness
  • Diaphoresis
  • Chest pain Pain Pain has accompanied humans since they first existed, first lamented as the curse of existence and later understood as an adaptive mechanism that ensures survival. Pain is the most common symptomatic complaint and the main reason why people seek medical care. Physiology of Pain
  • Shortness of breath

Diagnosis

  • Sudden-onset episodes of heart rate > 100/min caused by re-entry involving the atrium, AV node, or an accessory pathway
  • PSVTs are typically regular and between 140 and 250/min with narrow QRS complexes (< 120 ms)
  • Evaluate for signs and symptoms of hemodynamic (in)stability
  • Assess ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) for the type of narrow QRS complex tachycardia present: regular vs. irregular → P wave identification → atrial rate, P wave morphology, RP relationship, and AV relationship
Psvt: paroxysmal supraventricular tachycardias, ecg

Example of an ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) tracing of supraventricular tachycardia with a regular rhythm, hidden P wave morphology, narrow complex QRS < 120 ms, and a rate > 150/min (approximately 188/min).

Image: “SVT Lead II-2” by James Heilman, MD. License: Public Domain

Treatment

Treat hemodynamic instability via urgent direct current (DC) cardioversion if present.

AVNRT and AVRT:

  • Attempt vagal maneuvers (Valsalva, carotid massage) to slow conduction through the AV node.
  • If ineffective, IV adenosine is the first-line pharmacotherapy to terminate the rhythm.
  • IV calcium-channel blockers (e.g., verapamil), IV beta-blockers (e.g., propranolol), or digoxin may be used to slow conduction through the AV node in acute or preventative treatment if adenosine is not effective.
  • AVRT: Consider IV procainamide or IV amiodarone if persistent.

Wolff-Parkinson-White Syndrome

Etiology

  • Atrial impulses pass to the ventricles through both the AV node and an accessory pathway (bundle of Kent): leads to ventricular pre-excitation
  • Accessory pathway is often congenital in origin: failure of resorption of the myocardial syncytium at the annulus fibrosis during development
  • Characteristic ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) findings in WPW are observed due to the accessory pathway activating the ventricle slightly before the AV nodal pathway:
    • Shortened PR interval (< 0.12 s)
    • Slurred QRS upstroke (delta wave)
    • Widened QRS (> 120 ms)
Wolff-parkinson-white syndrome electrical pathways

Normal electrical pathway versus the abnormal accessory pathway that causes WPW

Image: “WPW” by Tom Lück. License: CC BY 3.0

Clinical presentation

  • The majority of patients are asymptomatic.
  • Patients can develop wide QRS-complex atrial fibrillation Atrial fibrillation Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation with rapid ventricular response (RVR) as part of the AVRT re-entry tachyarrhythmia Tachyarrhythmia A tachyarrhythmia is a rapid heart rhythm, regular or irregular, with a rate > 100 beats/min. Tachyarrhythmia may or may not be accompanied by symptoms of hemodynamic change. Tachyarrhythmias.
  • Accompanying palpitations, lightheadedness or dizziness, syncope or presyncope, chest pain Chest Pain Chest pain is one of the most common and challenging complaints that may present in an inpatient and outpatient setting. The differential diagnosis of chest pain is large and includes cardiac, gastrointestinal, pulmonary, musculoskeletal, and psychiatric etiologies. Chest Pain, or sudden cardiac arrest Cardiac arrest Cardiac arrest is the sudden, complete cessation of cardiac output with hemodynamic collapse. Patients present as pulseless, unresponsive, and apneic. Rhythms associated with cardiac arrest are ventricular fibrillation/tachycardia, asystole, or pulseless electrical activity. Cardiac Arrest can be present.

Diagnosis

  • Short PR interval (< 0.12 s) and a delta wave: confirming the diagnosis of the WPW pattern on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG)
  • Invasive electrophysiology testing: confirming the diagnosis in rare circumstances (e.g., short effective refractory periods in competitive athletes)
Tachyarrhythmia in wolff-parkinson-white syndrome

Normal sinus rhythm ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) obtained from a patient with Wolff-Parkinson-White Syndrome (WPW). Note delta waves and shortened PR interval.

Image: “Tachyarrhythmia in Wolff-Parkinson-White Syndrome” by University of California, Irvine, Department of Emergency Medicine, Irvine, California. License: CC BY 4.0

Treatment

Treatment is indicated in patients with symptomatic tachyarrhythmias to prevent RVR.

  • Do not use AV-blocking agents to treat the tachyarrhythmia Tachyarrhythmia A tachyarrhythmia is a rapid heart rhythm, regular or irregular, with a rate > 100 beats/min. Tachyarrhythmia may or may not be accompanied by symptoms of hemodynamic change. Tachyarrhythmias as slowed conduction through the AV node will worsen conduction through the accessory pathway and can be fatal.
  • Drugs for aborting the arrhythmia:
    • Procainamide 
    • Amiodarone
  • Catheter ablation of the accessory pathway for long-term control
  • Digoxin and calcium channel blockers Calcium Channel Blockers Calcium channel blockers (CCBs) are a class of medications that inhibit voltage-dependent L-type calcium channels of cardiac and vascular smooth muscle cells. The inhibition of these channels produces vasodilation and myocardial depression. There are 2 major classes of CCBs: dihydropyridines and non-dihydropyridines. Class 4 Antiarrhythmic Drugs (Calcium Channel Blockers) are dangerous in WPW because they block the normal AV node and force conduction in an abnormal pathway.

Atrial Flutter and Atrial Fibrillation

Atrial flutter

  • Rapid, regular atrial activity at a rate of 180300/min 
  • Varying degrees of conduction block at the AV node (due to the refractory period)
  • Generally caused by re-entry over a circuit of tissue along the tricuspid valve annulus  →  depolarizes large amounts of the atria throughout the cycle
  • Diffuse atrial polarization leads to its characteristic “sawtooth” pattern on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG)

Atrial fibrillation

  • Irregular atrial rate so fast that there are no discernable P waves on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG)
  • Patients have an “irregularly irregular” ventricular rhythm.
  • Generally caused by re-entry in random circuits around the atria caused by abnormal electrical discharges that originate in the pulmonary veins Veins Veins are tubular collections of cells, which transport deoxygenated blood and waste from the capillary beds back to the heart. Veins are classified into 3 types: small veins/venules, medium veins, and large veins. Each type contains 3 primary layers: tunica intima, tunica media, and tunica adventitia. Veins
  • Complications: stroke, secondary to thrombus formation in the left atria
Atrial fibrillation

Example of an ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) tracing showing atrial fibrillation Atrial fibrillation Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation with irregularly irregular RR intervals and loss of P waves

Image by Lecturio.

Multifocal Atrial Tachycardia (MAT)

Etiology

  • 60% of cases are associated with significant pulmonary disease
    • Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD) ( COPD COPD Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD)) > pneumonia Pneumonia Pneumonia or pulmonary inflammation is an acute or chronic inflammation of lung tissue. Causes include infection with bacteria, viruses, or fungi. In more rare cases, pneumonia can also be caused through toxic triggers through inhalation of toxic substances, immunological processes, or in the course of radiotherapy. Pneumonia, pulmonary embolism Pulmonary Embolism Pulmonary embolism (PE) is a potentially fatal condition that occurs as a result of intraluminal obstruction of the main pulmonary artery or its branches. The causative factors include thrombi, air, amniotic fluid, and fat. In PE, gas exchange is impaired due to the decreased return of deoxygenated blood to the lungs. Pulmonary Embolism, etc. 
    • Associated cardiac disease (coronary, valvular, hypertensive)
  • Can also be associated with hypokalemia Hypokalemia Hypokalemia is defined as plasma potassium (K+) concentration < 3.5 mEq/L. Homeostatic mechanisms maintain plasma concentration between 3.5-5.2 mEq/L despite marked variation in dietary intake. Hypokalemia can be due to renal losses, GI losses, transcellular shifts, or poor dietary intake. Hypokalemia, hypomagnesemia, medications (e.g., isoproterenol, aminophylline, theophylline), chronic renal failure
  • Multiple atrial origin sites cause different and unique P wave morphology.

Clinical presentation

  • Symptoms predominantly relate to the underlying precipitating illness rather than the arrhythmia.
  • Multifocal atria tachycardia can worsen systemic oxygenation in patients with advanced pulmonary disease and exacerbate heart disease.
    • Cardiac decompensation: angina, dyspnea Dyspnea Dyspnea is the subjective sensation of breathing discomfort. Dyspnea is a normal manifestation of heavy physical or psychological exertion, but also may be caused by underlying conditions (both pulmonary and extrapulmonary). Dyspnea, orthopnea

Diagnosis

  • Atrial rate > 100/min
  • Three or more distinct P-wave morphologies on ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG)
    • Each unique P wave morphology indicates a different atrial origin site.
    • P waves return to baseline, separated by isoelectric intervals.
  • P-P intervals, P-R duration, and R-R intervals that vary
Multifocal atrial tachycardia

ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) of a 3-year-old child who developed multifocal atrial tachycardia following an iatrogenic overdose of epinephrine accidentally administered intravenously.
Notice the different P-wave morphologies; flat (junctional), negative, and positive p-waves are evident (arrows).

Image: “ ECG ECG An electrocardiogram (ECG) is a graphic representation of the electrical activity of the heart plotted against time. Adhesive electrodes are affixed to the skin surface allowing measurement of cardiac impulses from many angles. The ECG provides 3-dimensional information about the conduction system of the heart, the myocardium, and other cardiac structures. Normal Electrocardiogram (ECG) findings” by Department of Pediatrics, College of Medicine and Health Science, United Arab Emirates University, Al-Ain, UAE. License: CC BY 2.0

Treatment

  • Aimed at underlying disease: magnesium and potassium replacement
  • Calcium channel blockers (e.g., verapamil) and beta-blockers (e.g., metoprolol) can be used with caution related to the underlying disease (avoid beta-blockers in lung disease)
  • Ablation:
    • Rarely required as episodes are brief and resolve with correction of the underlying abnormality
    • Indicated in persistent symptomatic MAT if the patient does not respond to or cannot tolerate pharmacotherapy

Clinical Relevance

The following conditions may be associated with the development of tachyarrhythmias:

  • Hyperthyroidism: an excess of thyroid hormones Thyroid hormones The 2 primary thyroid hormones are triiodothyronine (T3) and thyroxine (T4). These hormones are synthesized and secreted by the thyroid, and they are responsible for stimulating metabolism in most cells of the body. Their secretion is regulated primarily by thyroid-stimulating hormone (TSH), which is produced by the pituitary gland. Thyroid Hormones T3 and T4. Can promote the development of tachyarrhythmias, particularly atrial fibrillation Atrial fibrillation Atrial fibrillation (AF or Afib) is a supraventricular tachyarrhythmia and the most common kind of arrhythmia. It is caused by rapid, uncontrolled atrial contractions and uncoordinated ventricular responses. Atrial Fibrillation
  • Structural heart disease: can be arrhythmogenic; patients should be evaluated with echocardiography. Structural abnormalities may be a consequence of congestive heart failure Congestive heart failure Congestive heart failure refers to the inability of the heart to supply the body with normal cardiac output to meet metabolic needs. Echocardiography can confirm the diagnosis and give information about the ejection fraction. Congestive Heart Failure, myocardial infarction Myocardial infarction MI is ischemia and death of an area of myocardial tissue due to insufficient blood flow and oxygenation, usually from thrombus formation on a ruptured atherosclerotic plaque in the epicardial arteries. Clinical presentation is most commonly with chest pain, but women and patients with diabetes may have atypical symptoms. Myocardial Infarction, or valvular heart disease. 
  • COPD COPD Chronic obstructive pulmonary disease (COPD) is a lung disease characterized by progressive, largely irreversible airflow obstruction. The condition usually presents in middle-aged or elderly persons with a history of cigarette smoking. Signs and symptoms include prolonged expiration, wheezing, diminished breath sounds, progressive dyspnea, and chronic cough. Chronic Obstructive Pulmonary Disease (COPD): a spectrum of conditions characterized by irreversible airflow limitation correlated to smoking. The condition is a result of obstructive inflammation Inflammation Inflammation is a complex set of responses to infection and injury involving leukocytes as the principal cellular mediators in the body's defense against pathogenic organisms. Inflammation is also seen as a response to tissue injury in the process of wound healing. The 5 cardinal signs of inflammation are pain, heat, redness, swelling, and loss of function. Inflammation of the small airways as well as changes in the lung parenchyma and pulmonary vasculature. Advanced pulmonary disease is associated with the development of multifocal atrial tachycardia. 
  • Intoxication/ingestion: Numerous pharmacologic and illicit drugs may lead to sinus tachycardia or promote arrhythmias. 
  • Electrolyte abnormalities: Several abnormalities are associated with the development of ventricular tachyarrhythmias, including hypokalemia Hypokalemia Hypokalemia is defined as plasma potassium (K+) concentration < 3.5 mEq/L. Homeostatic mechanisms maintain plasma concentration between 3.5-5.2 mEq/L despite marked variation in dietary intake. Hypokalemia can be due to renal losses, GI losses, transcellular shifts, or poor dietary intake. Hypokalemia and hypomagnesemia.

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