Long QT Syndrome

Long QT syndrome (LQTS) is a disorder of ventricular myocardial repolarization that produces QT prolongation on 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)). Long QT syndrome is associated with an increased risk of developing life-threatening cardiac arrhythmias, specifically torsades de pointes. The condition may be congenital or acquired. Congenital LQTS is attributed to genetic mutations affecting cardiac ion channels. Acquired LQTS usually results from drug therapy and/or electrolyte abnormalities. Patients can be asymptomatic or present with 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, seizures Seizures A seizure is abnormal electrical activity of the neurons in the cerebral cortex that can manifest in numerous ways depending on the region of the brain affected. Seizures consist of a sudden imbalance that occurs between the excitatory and inhibitory signals in cortical neurons, creating a net excitation. The 2 major classes of seizures are focal and generalized. Seizures, and even sudden cardiac death. Diagnosis is established with 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) along with medical and family history, laboratory workup, and other cardiac tests. Treatment is determined by etiology. Acquired LQTS requires removal of the offending drug and correction of electrolyte abnormalities. Congenital LQTS management involves avoidance of triggers of arrhythmia, intake of beta-blockers, and placement of an implantable cardioverter-defibrillator (ICD).

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Editorial responsibility: Stanley Oiseth, Lindsay Jones, Evelin Maza

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Definitions

  • Long QT syndrome (LQTS): a ventricular electrical disorder characterized by delayed myocardial repolarization and demonstrated as prolonged QT interval on 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))
  • QT interval: reflects the average duration of a ventricular action potential
  • Normal QT interval:
    • On average: 400440 milliseconds
    • After puberty Puberty Puberty is a complex series of physical, psychosocial, and cognitive transitions usually experienced by adolescents (11-19 years of age). Puberty is marked by a growth in stature and the development of secondary sexual characteristics, achievement of fertility, and changes in most body systems. Puberty, women tend to have a longer QT interval than men.
  • Prolonged QT interval:
    • Males:
      • Normal: ≤ 430 milliseconds
      • Borderline prolonged QT interval: 431450 milliseconds
      • Prolonged QT interval: > 450 milliseconds
    • Females:
      • Normal: ≤ 450 milliseconds
      • Borderline prolonged QT interval: 451470 milliseconds
      • Prolonged QT interval: > 470 milliseconds
  • Torsades de pointes:
    • A life-threatening arrhythmia associated with LQTS
    • Form of polymorphic ventricular tachycardia Ventricular tachycardia Ventricular tachycardia is any heart rhythm faster than 100 beats/min, with 3 or more irregular beats in a row, arising distal to the bundle of His. Ventricular tachycardia is the most common form of wide-complex tachycardia, and it is associated with a high mortality rate. Ventricular Tachycardia
    • Caused by early after-depolarizations
    • Irregular QRS complexes twisting around the isoelectric line (torsade de pointes = “twisting of points”)
    • Rate of 160–250/min
    • Often terminates spontaneously, but can lead to sudden cardiac death

Etiology

Congenital long QT syndrome

Pathophysiology:

  • Defects in genes coding for ion channels (i.e., cardiac channelopathies)
    • Change in flow of positive ions affects repolarizing current in cardiomyocytes → prolongs the action potential (QT prolongation) → leads to early after-depolarization →  increased risk of torsades de pointes 
    • These genetic mutations account for 80% of LQTS cases: 
      • Loss-of-function mutations in KCNQ1-encoded and KCNH2-encoded  potassium channels: prolong action potential duration by reducing K efflux
      • Gain-of-function mutations in the SCN5A-encoded sodium channels: prolong action potential duration by the contribution of increased late sodium currents (which raises Na [sodium] influx)
  • Sympathetic innervation of the heart:
    • A trigger for torsades de pointes is a surge in sympathetic tone (such as an extreme emotional event).
    • Stimulation of left stellate ganglion prolongs the QT interval 
    • Not found in acquired LQTS

Types of congenital LQTS:

  1. Type 1 is the most common congenital form.
    • Up to 45% of LQTS cases
    • Defect in KCNQ1 gene
  2. Type 2
    • Up to 40% of LQTS cases
    • Defect in KCNH2 gene
  3. Type 3
    • Up to 10% of LQTS cases
    • Defect in SCN5A gene

Variety of associated conditions:

  • Romano-Ward syndrome: 99% of cases; congenital LQTS without extracardiac manifestations ( autosomal dominant Autosomal dominant Autosomal inheritance, both dominant and recessive, refers to the transmission of genes from the 22 autosomal chromosomes. Autosomal dominant diseases are expressed when only 1 copy of the dominant allele is inherited. Autosomal Recessive and Autosomal Dominant Inheritance)
  • Jervell and Lange-Nielsen syndrome: congenital LQTS + sensorineural hearing loss Hearing loss Hearing loss, also known as hearing impairment, is any degree of impairment in the ability to apprehend sound as determined by audiometry to be below normal hearing thresholds. Clinical presentation may occur at birth or as a gradual loss of hearing with age, including a short-term or sudden loss at any point. Hearing Loss (autosomal recessive)
  • Anderson-Tawil syndrome: congenital LQTS + periodic paralysis
  • Timothy syndrome: congenital LQTS + cutaneous syndactyly + autism

Acquired long QT syndrome

  • Iatrogenic/pharmacologic
    • Most common cause
    • LQTS caused by blocking potassium outflow during the rapid repolarization phase:
      • Antiarrhythmic drugs
      • Antibiotics ( macrolides Macrolides Macrolides and ketolides are antibiotics that inhibit bacterial protein synthesis by binding to the 50S ribosomal subunit and blocking transpeptidation. These antibiotics have a broad spectrum of antimicrobial activity but are best known for their coverage of atypical microorganisms. Macrolides and Ketolides, fluoroquinolones Fluoroquinolones Fluoroquinolones are a group of broad-spectrum, bactericidal antibiotics inhibiting bacterial DNA replication. Fluoroquinolones cover gram-negative, anaerobic, and atypical organisms, as well as some gram-positive and multidrug-resistant (MDR) organisms. Fluoroquinolones, antifungals, HIV antiretroviral drugs, antimalarial drugs Antimalarial drugs Malaria, a vector-borne parasitic disease caused by Plasmodium spp., is transmitted via injection of sporozoites or immature forms of the parasite into a person's bloodstream. Sporozoites then infect the hepatocytes and differentiate into schizonts, which subsequently rupture, and merozoites invade red blood cells. Antimalarial Drugs)
      • Antihistamines Antihistamines Antihistamines are drugs that target histamine receptors, particularly H1 and H2 receptors. H1 antagonists are competitive and reversible inhibitors of H1 receptors. First-generation antihistamines cross the blood-brain barrier and can cause sedation. Antihistamines (older nonsedating antihistamines, e.g., terfenadine)
      • Opioids Opioids Opiates are drugs that are derived from the sap of the opium poppy. Opiates have been used since antiquity for the relief of acute severe pain. Opioids are synthetic opiates with properties that are substantially similar to those of opiates. Opioid Analgesics (methadone, fentanyl)
      • Psychotropic agents (antidepressants, antipsychotics)
      • Gastric motility drugs (cisapride), antiemetics Antiemetics Antiemetics are medications used to treat and/or prevent nausea and vomiting. These drugs act on different target receptors. The main classes include benzodiazepines, corticosteroids, atypical antipsychotics, cannabinoids, and antagonists of the following receptors: serotonin, dopamine, and muscarinic and neurokinin receptors. Antiemetics (ondansetron)
      • Antineoplastics
      • Beta-2 agonists
      • Diuretics (due to resultant electrolyte abnormalities)
  • Metabolic disorders:
    • Electrolyte disturbances: 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, hypocalcemia Hypocalcemia Hypocalcemia, a serum calcium < 8.5 mg/dL, can result from various conditions. The causes may include hypoparathyroidism, drugs, disorders leading to vitamin D deficiency, and more. Calcium levels are regulated and affected by different elements such as dietary intake, parathyroid hormone (PTH), vitamin D, pH, and albumin. Presentation can range from an asymptomatic (mild deficiency) to a life-threatening condition (acute, significant deficiency). Hypocalcemia, hypomagnesemia
    • Hypothyroidism Hypothyroidism Hypothyroidism is a condition characterized by a deficiency of thyroid hormones. Iodine deficiency is the most common cause worldwide, but Hashimoto's disease (autoimmune thyroiditis) is the leading cause in non-iodine-deficient regions. Hypothyroidism
    • Anorexia nervosa Anorexia Nervosa Anorexia nervosa is an eating disorder marked by self-imposed starvation and inappropriate dietary habits due to a morbid fear of weight gain and disturbed perception of body shape and weight. Patients have strikingly low BMI and diverse physiological and psychological complications. Anorexia Nervosa, starvation (due to resultant electrolyte abnormalities)
  • Bradyarrhythmias Bradyarrhythmias Bradyarrhythmia is a rhythm in which the heart rate is less than 60/min. Bradyarrhythmia can be physiologic, without symptoms or hemodynamic change. Pathologic bradyarrhythmia results in reduced cardiac output and hemodynamic instability causing syncope, dizziness, or dyspnea. Bradyarrhythmias:
    • Sinus node dysfunction
    • Atrioventricular (AV) block (2nd or 3rd degree)
  • Other
    • 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 ( MI MI 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)
    • Intracranial disease 
    • HIV infection HIV infection Human immunodeficiency virus (HIV), a single-stranded RNA virus belonging to the Retroviridae family, is the etiologic agent of acquired immunodeficiency syndrome (AIDS). The human immunodeficiency virus is a sexually transmitted or blood-borne infection that attacks CD4+ T lymphocyte cells, macrophages, and dendritic cells, leading to eventual immunodeficiency. HIV Infection and AIDS 
    • Hypothermia Hypothermia Hypothermia can be defined as a drop in the core body temperature below 35°C (95°F) and is classified into mild, moderate, severe, and profound forms based on the degree of temperature decrease. Hypothermia
    • Toxic exposure (e.g., organophosphates)

Clinical Manifestations

Congenital long QT syndrome

  • Often diagnosed in the first 3 decades of life
  • Most commonly asymptomatic
    Diagnosis may be made:
    • When a patient seeks medical attention after a cardiac event in a family member
    • As an incidental finding in 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) done for another indication
  • Those with symptoms present with:
    • Syncope
    • Syncope followed by seizure (may be misdiagnosed as primary seizure disorder)
    • 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 (SCA)
    • In rare cases, the sentinel event is sudden cardiac death ( SCD SCD Sickle cell disease (SCD) is a group of genetic disorders in which an abnormal Hb molecule (HbS) transforms RBCs into sickle-shaped cells, resulting in chronic anemia, vasoocclusive episodes, pain, and organ damage. Sickle Cell Disease).
  • LQTS type 1: 
    • Cardiac events preceded by exercise (62% of events) or stress
    • Swimming is a highly specific trigger!
  • LQTS type 2:
    • Arrhythmia after an extreme emotional event, exercise, or auditory stimuli (sudden noise or alarm/telephone ringing)
    • Postpartum cardiac event: almost exclusively in LQTS 2
    • Cardiac events can also occur at rest or during sleep Sleep Sleep is a reversible phase of diminished responsiveness, motor activity, and metabolism. This process is a complex and dynamic phenomenon, occurring in 4-5 cycles a night, and generally divided into non-rapid eye movement (NREM) sleep and REM sleep stages. Physiology of Sleep.
  • LQTS type 3
    • The majority of cardiac events occur during rest or sleep Sleep Sleep is a reversible phase of diminished responsiveness, motor activity, and metabolism. This process is a complex and dynamic phenomenon, occurring in 4-5 cycles a night, and generally divided into non-rapid eye movement (NREM) sleep and REM sleep stages. Physiology of Sleep.

Acquired long QT syndrome

  • Symptoms are only present with an episode of arrhythmia.
  • Symptoms vary with the rate and duration of torsades de pointes as well as with comorbidities:
    • Palpitations
    • Light-headedness or presyncope
    • Syncope 
    • 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

Diagnosis

The diagnosis of long QT syndrome can be made via 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) of the patient and/or 1st-degree relatives.

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

  • Prolonged QTc (corrected QT interval)
    • The QT interval needs to be “corrected” to account for varying heart rates and is often automatically reported as the QTc.
    • Correction formula: QTc = QT interval ÷ √RR interval (in sec)
    • QTc interval > 450 ms in males
    • QTc interval > 470 ms in females
  • LQTS can degenerate into fatal arrhythmias, especially torsades de pointes:
    • Short-lived but can have multiple successive episodes
    • Can progress to ventricular fibrillation Ventricular fibrillation Ventricular fibrillation (VF or V-fib) is a type of ventricular tachyarrhythmia (> 300/min) often preceded by ventricular tachycardia. In this arrhythmia, the ventricle beats rapidly and sporadically. The ventricular contraction is uncoordinated, leading to a decrease in cardiac output and immediate hemodynamic collapse. Ventricular Fibrillation
    • 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 include:
      • Prolonged QTc in last sinus beat preceding onset of arrhythmia
      • Tachycardia of 160250/min
      • Wide QRS complexes (> 120 ms) with QRS axis rotating over a sequence of 520 beats
      • Irregular RR interval
  • Ambulatory 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) monitoring: may provide corroborative information for suspected cases of congenital LQTS

Exercise testing

  • To assess exercise-associated arrhythmias
  • Check QT responses (exercise and recovery) and changes in T wave
  • Variable Variable Variables represent information about something that can change. The design of the measurement scales, or of the methods for obtaining information, will determine the data gathered and the characteristics of that data. As a result, a variable can be qualitative or quantitative, and may be further classified into subgroups. Types of Variables response with type of congenital LQTS
  • QTc > 470 ms at 25 minute recovery is suggestive of LQTS 1 (where cardiac events commonly occur during exercise)

Genetic analysis

  • For intermediate and highly suspicious cases of congenital LQTS based on clinical presentation, family history, and 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 asymptomatic patients with serial ECGs showing QTc > 460 ms

Additional tests

  • Medication review
  • Laboratory tests (metabolic panel, thyroid-stimulating hormone [TSH])
  • Other cardiac workup based on probable cause (myocardial perfusion, echocardiogram)

Management

Congenital LQTS

  • Reduce the risk of fatal arrhythmias:
    • Avoid QT-prolonging drugs
    • Electrolyte repletion
    • Avoid triggers of arrhythmia (swimming/exercise, emotional distress, noise; LQTS specialist consult for sports participation recommended)
  • First-line medications: beta-blockers (propranolol or nadolol)
  • Left cardiac sympathetic denervation:
    • Rarely performed
    • May work in some patients who do not respond to or cannot tolerate beta-blockers
    • Not curative; high-risk patients will still need an implantable cardioverter-defibrillator (ICD)
  • Recurrent symptoms despite medical therapy warrant placement of an ICD.

Acquired LQTS

  • Correct treatable medical causes quickly (e.g., electrolyte abnormalities and metabolic disturbances)!
  • Remove the offending drug.

In the setting of torsades de pointes

  • Hemodynamically stable patients:
    •  IV magnesium sulfate, cardiac monitoring
    • Overdrive pacing: for those not responsive to IV magnesium
  • Hemodynamically unstable patients:
    • Defibrillation
    • IV magnesium sulfate

Clinical Relevance

Predisposing factors

The following medical conditions may commonly predispose QT prolongation:

  • Hypothyroidism Hypothyroidism Hypothyroidism is a condition characterized by a deficiency of thyroid hormones. Iodine deficiency is the most common cause worldwide, but Hashimoto's disease (autoimmune thyroiditis) is the leading cause in non-iodine-deficient regions. Hypothyroidism: the deficiency of T3 and T4. Hashimoto’s disease (autoimmune thyroiditis Thyroiditis Thyroiditis is a catchall term used to describe a variety of conditions that have inflammation of the thyroid gland in common. It includes pathologies that cause an acute illness with severe thyroid pain (e.g., subacute thyroiditis and infectious thyroiditis) as well as conditions in which there is no clinically evident inflammation and the manifestations primarily reflect thyroid dysfunction or a goiter (e.g., painless thyroiditis and fibrous Riedel's thyroiditis). Thyroiditis) is the leading cause of hypothyroidism in non-iodine deficient regions. Hypothyroidism Hypothyroidism Hypothyroidism is a condition characterized by a deficiency of thyroid hormones. Iodine deficiency is the most common cause worldwide, but Hashimoto's disease (autoimmune thyroiditis) is the leading cause in non-iodine-deficient regions. Hypothyroidism is diagnosed by the estimation of TSH and free T4. It is treated by the administration of synthetic T4.
  • Hypokalemia: plasma potassium < 3.5 mEq/L. Risk factors for 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 include aging, poor dietary intake, diuretic use, and gastrointestinal losses. 
  • Hypocalcemia: low serum ionized calcium levels. Calcium levels are regulated by the parathyroid hormone (PTH), which is secreted by the parathyroid gland. The presentation of patients with hypocalcemia Hypocalcemia Hypocalcemia, a serum calcium < 8.5 mg/dL, can result from various conditions. The causes may include hypoparathyroidism, drugs, disorders leading to vitamin D deficiency, and more. Calcium levels are regulated and affected by different elements such as dietary intake, parathyroid hormone (PTH), vitamin D, pH, and albumin. Presentation can range from an asymptomatic (mild deficiency) to a life-threatening condition (acute, significant deficiency). Hypocalcemia can range from asymptomatic to life-threatening dysrhythmias.

Differential diagnosis

The following conditions may be included in a differential diagnosis for prolonged QT interval:

  • Vasovagal 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: a drop in blood pressure resulting in poor blood and oxygen flow to the brain that results in temporary loss of consciousness. 
  • 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: obstruction of coronary arteries Arteries Arteries are tubular collections of cells that transport oxygenated blood and nutrients from the heart to the tissues of the body. The blood passes through the arteries in order of decreasing luminal diameter, starting in the largest artery (the aorta) and ending in the small arterioles. Arteries are classified into 3 types: large elastic arteries, medium muscular arteries, and small arteries and arterioles. Arteries resulting in decreased blood supply to the myocardium. The typical presentation of MI MI 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 is 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, shortness of breath, and diaphoresis. Patients may have 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 sudden death.

Complications

Untreated QT prolongation may evolve into the following complications:

  • Torsades de pointes: a specific form of polymorphic ventricular tachycardia Ventricular tachycardia Ventricular tachycardia is any heart rhythm faster than 100 beats/min, with 3 or more irregular beats in a row, arising distal to the bundle of His. Ventricular tachycardia is the most common form of wide-complex tachycardia, and it is associated with a high mortality rate. Ventricular Tachycardia in patients with a long QT interval. It is characterized by rapid and irregular QRS complexes, which appear to be twisting around the baseline.
  • Ventricular tachycardia: a group of arrhythmias with heart rate > 100/min that originates from within the ventricle. There are 3 main types of ventricular tachyarrhythmias: ventricular fibrillation Ventricular fibrillation Ventricular fibrillation (VF or V-fib) is a type of ventricular tachyarrhythmia (> 300/min) often preceded by ventricular tachycardia. In this arrhythmia, the ventricle beats rapidly and sporadically. The ventricular contraction is uncoordinated, leading to a decrease in cardiac output and immediate hemodynamic collapse. Ventricular Fibrillation, monomorphic ventricular tachycardia Ventricular tachycardia Ventricular tachycardia is any heart rhythm faster than 100 beats/min, with 3 or more irregular beats in a row, arising distal to the bundle of His. Ventricular tachycardia is the most common form of wide-complex tachycardia, and it is associated with a high mortality rate. Ventricular Tachycardia, and polymorphic ventricular tachycardia Ventricular tachycardia Ventricular tachycardia is any heart rhythm faster than 100 beats/min, with 3 or more irregular beats in a row, arising distal to the bundle of His. Ventricular tachycardia is the most common form of wide-complex tachycardia, and it is associated with a high mortality rate. Ventricular Tachycardia
  • Cardiac arrest: the sudden complete cessation of cardiac activity with hemodynamic collapse. Cardiac rhythms known to produce a pulseless 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 are shockable rhythms ( ventricular fibrillation Ventricular fibrillation Ventricular fibrillation (VF or V-fib) is a type of ventricular tachyarrhythmia (> 300/min) often preceded by ventricular tachycardia. In this arrhythmia, the ventricle beats rapidly and sporadically. The ventricular contraction is uncoordinated, leading to a decrease in cardiac output and immediate hemodynamic collapse. Ventricular Fibrillation, pulseless ventricular tachycardia Ventricular tachycardia Ventricular tachycardia is any heart rhythm faster than 100 beats/min, with 3 or more irregular beats in a row, arising distal to the bundle of His. Ventricular tachycardia is the most common form of wide-complex tachycardia, and it is associated with a high mortality rate. Ventricular Tachycardia) and non-shockable rhythms (pulseless electrical activity, asystole). Rapid identification and intervention are critical to saving a patient’s life.

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