Atrioventricular block (AV block)

Epidemiology and Etiology

Epidemiology

• More common in the elderly
• 3rd-degree block is the rarest.
• 1st-degree and Mobitz type 1 Type 1 Spinal Muscular Atrophy 2nd-degree atrioventricular (AV) block can be seen in healthy patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship.

Etiology

• Pathologic:
  • Idiopathic Idiopathic Dermatomyositis fibrosis Fibrosis Any pathological condition where fibrous connective tissue invades any organ, usually as a consequence of inflammation or other injury. Bronchiolitis Obliterans and sclerosis Sclerosis A pathological process consisting of hardening or fibrosis of an anatomical structure, often a vessel or a nerve. Wilms Tumor of the conduction system (approximately 50% of cases)
  • 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 (approximately 40% of cases)
  • Cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Cardiomyopathy: Overview and Types:
    • Hypertrophic obstructive cardiomyopathy Cardiomyopathy Cardiomyopathy refers to a group of myocardial diseases associated with structural changes of the heart muscles (myocardium) and impaired systolic and/or diastolic function in the absence of other heart disorders (coronary artery disease, hypertension, valvular disease, and congenital heart disease). Cardiomyopathy: Overview and Types 
    • Sarcoidosis Sarcoidosis Sarcoidosis is a multisystem inflammatory disease that causes noncaseating granulomas. The exact etiology is unknown. Sarcoidosis usually affects the lungs and thoracic lymph nodes, but it can also affect almost every system in the body, including the skin, heart, and eyes, most commonly. Sarcoidosis 
    • Amyloidosis Amyloidosis Amyloidosis is a disease caused by abnormal extracellular tissue deposition of fibrils composed of various misfolded low-molecular-weight protein subunits. These proteins are frequently byproducts of other pathological processes (e.g., multiple myeloma). Amyloidosis
  • Myocarditis Myocarditis Myocarditis is an inflammatory disease of the myocardium, which may occur alone or in association with a systemic process. There are numerous etiologies of myocarditis, but all lead to inflammation and myocyte injury, most often leading to signs and symptoms of heart failure. Myocarditis:
    • Lyme disease Lyme disease Lyme disease is a tick-borne infection caused by the gram-negative spirochete Borrelia burgdorferi. Lyme disease is transmitted by the black-legged Ixodes tick (known as a deer tick), which is only found in specific geographic regions. Patient presentation can vary depending on the stage of the disease and may include a characteristic erythema migrans rash. Lyme Disease
    • Systemic lupus erythematosus Systemic lupus erythematosus Systemic lupus erythematosus (SLE) is a chronic autoimmune, inflammatory condition that causes immune-complex deposition in organs, resulting in systemic manifestations. Women, particularly those of African American descent, are more commonly affected. Systemic Lupus Erythematosus
    • Infective endocarditis Infective endocarditis Infective endocarditis (IE) is caused by infection or inflammation of the inner lining of the heart (endocardium), most commonly affecting the heart valves. Endocarditis
    • Other bacterial, viral, and parasitic causes
  • Congenital Congenital Chorioretinitis heart disease:
    • Atrial and AV septal defects
    • Neonatal lupus Neonatal Lupus Systemic Lupus Erythematosus 
  • Familial disease
  • 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 and hyperthyroidism Hyperthyroidism Hypersecretion of thyroid hormones from the thyroid gland. Elevated levels of thyroid hormones increase basal metabolic rate. Thyrotoxicosis and Hyperthyroidism
  • Hyperkalemia Hyperkalemia Hyperkalemia is defined as a serum potassium (K+) concentration >5.2 mEq/L. Homeostatic mechanisms maintain the serum K+ concentration between 3.5 and 5.2 mEq/L, despite marked variation in dietary intake. Hyperkalemia can be due to a variety of causes, which include transcellular shifts, tissue breakdown, inadequate renal excretion, and drugs. Hyperkalemia
  • Tumors and trauma
• Physiologic:
  • Increased vagal tone (due to athletic training, sleep Sleep A readily reversible suspension of sensorimotor interaction with the environment, usually associated with recumbency and immobility. Physiology of Sleep, pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways, carotid sinus Carotid sinus The dilated portion of the common carotid artery at its bifurcation into external and internal carotids. It contains baroreceptors which, when stimulated, cause slowing of the heart, vasodilatation, and a fall in blood pressure. Carotid Arterial System: Anatomy massage, carotid sinus Carotid sinus The dilated portion of the common carotid artery at its bifurcation into external and internal carotids. It contains baroreceptors which, when stimulated, cause slowing of the heart, vasodilatation, and a fall in blood pressure. Carotid Arterial System: Anatomy hypersensitivity syndrome)
  • Heart tissue changes related to aging
• Iatrogenic Iatrogenic Any adverse condition in a patient occurring as the result of treatment by a physician, surgeon, or other health professional, especially infections acquired by a patient during the course of treatment. Anterior Cord Syndrome:
  • Cardiac surgery Cardiac surgery Cardiac surgery is the surgical management of cardiac abnormalities and of the great vessels of the thorax. In general terms, surgical intervention of the heart is performed to directly restore adequate pump function, correct inherent structural issues, and reestablish proper blood supply via the coronary circulation. Cardiac Surgery ( aortic valve Aortic valve The valve between the left ventricle and the ascending aorta which prevents backflow into the left ventricle. Heart: Anatomy surgery)
  • Transcatheter cardiac procedures
  • Cardiac ablation therapy
  • Medications:
    • Beta blockers 
    • Non-dihydropyridine Non-Dihydropyridine Pulmonary Hypertension Drugs calcium Calcium A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes. Electrolytes channel blockers 
    • Digoxin Digoxin A cardiotonic glycoside obtained mainly from digitalis lanata; it consists of three sugars and the aglycone digoxigenin. Digoxin has positive inotropic and negative chronotropic activity. It is used to control ventricular rate in atrial fibrillation and in the management of congestive heart failure with atrial fibrillation. Its use in congestive heart failure and sinus rhythm is less certain. The margin between toxic and therapeutic doses is small. Cardiac Glycosides 
    • Adenosine Adenosine A nucleoside that is composed of adenine and d-ribose. Adenosine or adenosine derivatives play many important biological roles in addition to being components of DNA and RNA. Adenosine itself is a neurotransmitter. Class 5 Antiarrhythmic Drugs 
    • Antiarrhythmics ( amiodarone Amiodarone An antianginal and class III antiarrhythmic drug. It increases the duration of ventricular and atrial muscle action by inhibiting potassium channels and voltage-gated sodium channels. There is a resulting decrease in heart rate and in vascular resistance. Pulmonary Fibrosis, quinidine Quinidine An optical isomer of quinine, extracted from the bark of the cinchona tree and similar plant species. This alkaloid dampens the excitability of cardiac and skeletal muscles by blocking sodium and potassium currents across cellular membranes. It prolongs cellular action potentials, and decreases automaticity. Quinidine also blocks muscarinic and alpha-adrenergic neurotransmission. Class 1 Antiarrhythmic Drugs (Sodium Channel Blockers), procainamide Procainamide A class ia antiarrhythmic drug that is structurally-related to procaine. Class 1 Antiarrhythmic Drugs (Sodium Channel Blockers), disopyramide Disopyramide A class I antiarrhythmic agent (one that interferes directly with the depolarization of the cardiac membrane and thus serves as a membrane-stabilizing agent) with a depressant action on the heart similar to that of guanidine. It also possesses some anticholinergic and local anesthetic properties. Class 1 Antiarrhythmic Drugs (Sodium Channel Blockers))

Pathophysiology and Classification

Atrioventricular (AV) block is a delay, or interruption, in the electrical impulse as it passes from the atria to the ventricles through the AV node or the His-Purkinje system. Atrioventricular block is classified based on the severity of the disruption.

First-degree AV block

• Delayed or prolonged conduction through the AV node; not considered a true block
• Defined as a prolonged PR interval PR interval Electrocardiogram (ECG) (> 0.2 sec)
• May be non-pathologic

Second-degree AV block

Second-degree AV block is further divided into 2 subtypes:

• Mobitz type 1 Type 1 Spinal Muscular Atrophy (also known as “Wenckebach”):
  • Progressive increase in the delay of conduction until a block forms at the AV node → conduction is not transmitted through the AV node → the QRS complex QRS complex Electrocardiogram (ECG) is “dropped”
  • Usually the result of excess vagal tone of the AV node in athletes
• Mobitz type 2 Type 2 Spinal Muscular Atrophy: 
  • Intermittent block of conduction through the AV node → unchanged PR intervals with intermittent QRS complexes “dropped”
  • Almost always results from conduction system disease below the level of the AV node
  • Can deteriorate into 3rd-degree AV block

Third-degree (complete) AV block

• Complete failure of conduction between the atria and ventricles
• Results in AV dissociation Dissociation Defense Mechanisms: 
  • Atrial activation and ventricular activation are independent of each other.
  • Occurs because no atrial impulses reach the ventricles
• An escape Escape With constant immune mechanisms holding unstable tumor cells in equilibrium, tumor-cell variants may emerge. These cancer cells may express fewer antigens on their surfaces or lose their MHC class I expression.Variants may also protect themselves from T-cell attack via expression of IC molecules on their surfaces, like normal cells.Creation of an immunosuppressive state in the microenvironment is another way to grow without immunologic interference. Cancer Immunotherapy pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias occurs distal to the block:
  • Junctional escape Escape With constant immune mechanisms holding unstable tumor cells in equilibrium, tumor-cell variants may emerge. These cancer cells may express fewer antigens on their surfaces or lose their MHC class I expression.Variants may also protect themselves from T-cell attack via expression of IC molecules on their surfaces, like normal cells.Creation of an immunosuppressive state in the microenvironment is another way to grow without immunologic interference. Cancer Immunotherapy rhythm from above the His bundle
  • Ventricular escape Escape With constant immune mechanisms holding unstable tumor cells in equilibrium, tumor-cell variants may emerge. These cancer cells may express fewer antigens on their surfaces or lose their MHC class I expression.Variants may also protect themselves from T-cell attack via expression of IC molecules on their surfaces, like normal cells.Creation of an immunosuppressive state in the microenvironment is another way to grow without immunologic interference. Cancer Immunotherapy rhythm from below the His bundle
• Atrial and ventricular contractions become uncoordinated → poor movement of blood → poor cardiac output Cardiac output The volume of blood passing through the heart per unit of time. It is usually expressed as liters (volume) per minute so as not to be confused with stroke volume (volume per beat). Cardiac Mechanics → heart failure Heart Failure A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction. Total Anomalous Pulmonary Venous Return (TAPVR), hemodynamic instability, or cardiovascular collapse

Clinical Presentation

• 1st-degree and Mobitz type 1 Type 1 Spinal Muscular Atrophy 2nd-degree AV block are usually asymptomatic. 
• Mobitz type 2 Type 2 Spinal Muscular Atrophy 2nd-degree AV block and 3rd-degree AV block may present with:
  • Chest pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways
  • Bradycardia Bradycardia 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
  • Nausea Nausea An unpleasant sensation in the stomach usually accompanied by the urge to vomit. Common causes are early pregnancy, sea and motion sickness, emotional stress, intense pain, food poisoning, and various enteroviruses. Antiemetics 
  • Presyncope Presyncope Syncope or 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 (Stokes-Adams syndrome)
  • Hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension 
  • Pallor
  • Blurry vision Vision Ophthalmic Exam
  • Confusion
  • Fatigue Fatigue The state of weariness following a period of exertion, mental or physical, characterized by a decreased capacity for work and reduced efficiency to respond to stimuli. Fibromyalgia
  • 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
  • Dizziness Dizziness An imprecise term which may refer to a sense of spatial disorientation, motion of the environment, or lightheadedness. Lateral Medullary Syndrome (Wallenberg Syndrome)
  • 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
  • Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with 3rd-degree block may have cannon A-waves (atrial-wave): 
    • Waves seen occasionally in the jugular 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: Histology
    • Due to the right atrium contracting against a closed tricuspid valve Tricuspid valve The valve consisting of three cusps situated between the right atrium and right ventricle of the heart. Heart: Anatomy

Diagnosis

The diagnosis is made by electrocardiography Electrocardiography Recording of the moment-to-moment electromotive forces of the heart as projected onto various sites on the body’s surface, delineated as a scalar function of time. The recording is monitored by a tracing on slow moving chart paper or by observing it on a cardioscope, which is a cathode ray tube display. 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. Electrocardiogram (ECG)), and the findings depend on the type of AV block.

First-degree AV block

• All P waves are followed by a QRS complex QRS complex Electrocardiogram (ECG).
• PR interval PR interval Electrocardiogram (ECG) > 0.2 sec

Second-degree AV block, Mobitz type 1 Type 1 Spinal Muscular Atrophy (Wenckebach)

• Irregular rhythm
• PR interval PR interval Electrocardiogram (ECG) progressively lengthens.
• Failure of the AV node to conduct the atrial impulse results in a missing QRS complex QRS complex Electrocardiogram (ECG).
• AV node conduction resumes with the next beat, and repeats the cycle Cycle The type of signal that ends the inspiratory phase delivered by the ventilator Invasive Mechanical Ventilation.
• Mnemonic: “Longer, longer, longer, drop! This must be a Wenckebach!”
• 2:1 AV block is difficult to differentiate from Mobitz type 2 Type 2 Spinal Muscular Atrophy, but the following may be clues:
  • A PR interval PR interval Electrocardiogram (ECG) > 0.3 sec
  • Enhanced AV nodal conduction with atropine Atropine An alkaloid, originally from atropa belladonna, but found in other plants, mainly solanaceae. Hyoscyamine is the 3(s)-endo isomer of atropine. Anticholinergic Drugs
  • Worsened with carotid massage Carotid massage Supraventricular Tachycardias by slowing AV nodal conduction

Second-degree AV block, Mobitz type 2 Type 2 Spinal Muscular Atrophy

• Consistent, unchanging PR intervals
• An abrupt failure of P wave P wave Electrocardiogram (ECG) conduction results in a missing QRS complex QRS complex Electrocardiogram (ECG).
• The rhythm on either side of the drop is normal.
• Can form a pattern (e.g., a P:QRS conduction ratio of 3:1)
• May progress to high-grade 2nd-degree AV block, where multiple P waves in a row are blocked

Third-degree AV block

• No relationship Relationship A connection, association, or involvement between 2 or more parties. Clinician–Patient Relationship between the P waves and QRS complexes
• 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 PR interval PR interval Electrocardiogram (ECG)
• QRS, P-P, and R-R intervals are constant.
• QRS complexes are due to junctional or ventricular escape Escape With constant immune mechanisms holding unstable tumor cells in equilibrium, tumor-cell variants may emerge. These cancer cells may express fewer antigens on their surfaces or lose their MHC class I expression.Variants may also protect themselves from T-cell attack via expression of IC molecules on their surfaces, like normal cells.Creation of an immunosuppressive state in the microenvironment is another way to grow without immunologic interference. Cancer Immunotherapy rhythms:
  • Junctional rhythms will have a rate of 40–60 beats/min.
  • Ventricular rhythms will have a rate of 20–40 beats/min.
  • QRS complexes may be narrow or wide, depending on the site of occurrence.

Management

First-degree AV block

• No treatment needed in asymptomatic patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship
• Evaluate for underlying conditions and reversible causes. 
• Regular Regular Insulin follow-up 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. Electrocardiogram (ECG) to monitor for progression
• Pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias placement is usually not indicated; exceptions include:
  • Patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with wide QRS complexes due to a conduction delay below the AV node, which may progress to 2nd- and 3rd-degree heart block
  • Symptomatic patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship with “pseudo-pacemaker syndrome” due to the loss of AV synchrony: 
    • Due to atrial contraction against a closed mitral valve Mitral valve The valve between the left atrium and left ventricle of the heart. Heart: Anatomy or when the atrial contraction occurs right after ventricular systole Ventricular systole Cardiac Cycle
    • Leads to hemodynamic changes (systemic hypotension Hypotension Hypotension is defined as low blood pressure, specifically < 90/60 mm Hg, and is most commonly a physiologic response. Hypotension may be mild, serious, or life threatening, depending on the cause. Hypotension, elevated pulmonary artery Pulmonary artery The short wide vessel arising from the conus arteriosus of the right ventricle and conveying unaerated blood to the lungs. Lungs: Anatomy pressure, cannon A-waves)

Second-degree AV block, Mobitz type 1 Type 1 Spinal Muscular Atrophy (Wenckebach)

• Asymptomatic (most patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship): same as 1st-degree AV block treatment 
• Symptomatic:
  • Stable: 
    • Continuous monitoring with transcutaneous pacing pads in place in case of deterioration 
    • Identify and treat reversible causes.
    • If persistent and there are no reversible causes, then permanent pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias placement
  • Unstable: 
    • Atropine Atropine An alkaloid, originally from atropa belladonna, but found in other plants, mainly solanaceae. Hyoscyamine is the 3(s)-endo isomer of atropine. Anticholinergic Drugs 
    • If no response, then temporary transcutaneous pacing
    • Dopamine Dopamine One of the catecholamine neurotransmitters in the brain. It is derived from tyrosine and is the precursor to norepinephrine and epinephrine. Dopamine is a major transmitter in the extrapyramidal system of the brain, and important in regulating movement. Receptors and Neurotransmitters of the CNS infusion is an alternative.
    • Pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias placement is pursued if there is no reversible etiology.

Second-degree AV block, Mobitz type 2 Type 2 Spinal Muscular Atrophy

• Same treatment as with symptomatic Mobitz type 1 Type 1 Spinal Muscular Atrophy patients Patients Individuals participating in the health care system for the purpose of receiving therapeutic, diagnostic, or preventive procedures. Clinician–Patient Relationship
• Requires careful monitoring because 2nd-degree AV block, Mobitz type 2 Type 2 Spinal Muscular Atrophy can progress to 3rd-degree AV block 
• Will often lead to pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias placement unless there is a reversible cause

Third-degree AV block

• Treatment of stable and unstable patients Unstable Patients Blunt Chest Trauma is the same as Mobitz type 2 Type 2 Spinal Muscular Atrophy 2nd-degree AV block.
• Dobutamine Dobutamine A catecholamine derivative with specificity for beta-1 adrenergic receptors. Sympathomimetic Drugs may also be used in unstable patients Unstable Patients Blunt Chest Trauma presenting with heart failure Heart Failure A heterogeneous condition in which the heart is unable to pump out sufficient blood to meet the metabolic need of the body. Heart failure can be caused by structural defects, functional abnormalities (ventricular dysfunction), or a sudden overload beyond its capacity. Chronic heart failure is more common than acute heart failure which results from sudden insult to cardiac function, such as myocardial infarction. Total Anomalous Pulmonary Venous Return (TAPVR).
• Will require pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias placement unless there is a reversible cause

Differential Diagnosis

• Junctional rhythm: a rhythm originating in the AV junction due to slowing of the sinoatrial (SA) node or failure of electrical impulses to reach the ventricles. Electrocardiography Electrocardiography Recording of the moment-to-moment electromotive forces of the heart as projected onto various sites on the body’s surface, delineated as a scalar function of time. The recording is monitored by a tracing on slow moving chart paper or by observing it on a cardioscope, which is a cathode ray tube display. Electrocardiogram (ECG) findings include narrow QRS complexes, bradycardia Bradycardia 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, retrograde (or no) P waves, or AV dissociation Dissociation Defense Mechanisms. The P wave P wave Electrocardiogram (ECG) morphology, rate, and relationship Relationship A connection, association, or involvement between 2 or more parties. Clinician–Patient Relationship to the QRS complex QRS complex Electrocardiogram (ECG) will help determine if the junctional rhythm is related to the AV block. Treatment is based on the cause and the stability of the patient. 
• Sinus node dysfunction Sinus node dysfunction A condition caused by dysfunctions related to the sinoatrial node including impulse generation (cardiac sinus arrest) and impulse conduction (sinoatrial exit block). It is characterized by persistent bradycardia, chronic atrial fibrillation, and failure to resume sinus rhythm following cardioversion. This syndrome can be congenital or acquired, particularly after surgical correction for heart defects. Bradyarrhythmias: a spectrum of SA node abnormalities causing alterations in electrical impulse formation and conduction, resulting in abnormal atrial rates. Symptoms include light-headedness, 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, and alternating periods of bradycardia Bradycardia 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 and tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children. Electrocardiography Electrocardiography Recording of the moment-to-moment electromotive forces of the heart as projected onto various sites on the body’s surface, delineated as a scalar function of time. The recording is monitored by a tracing on slow moving chart paper or by observing it on a cardioscope, which is a cathode ray tube display. Electrocardiogram (ECG) findings of severe bradycardia Bradycardia 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 pauses or arrests, junctional escape Escape With constant immune mechanisms holding unstable tumor cells in equilibrium, tumor-cell variants may emerge. These cancer cells may express fewer antigens on their surfaces or lose their MHC class I expression.Variants may also protect themselves from T-cell attack via expression of IC molecules on their surfaces, like normal cells.Creation of an immunosuppressive state in the microenvironment is another way to grow without immunologic interference. Cancer Immunotherapy rhythm, or alternating bradycardia Bradycardia 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 and tachycardia Tachycardia Abnormally rapid heartbeat, usually with a heart rate above 100 beats per minute for adults. Tachycardia accompanied by disturbance in the cardiac depolarization (cardiac arrhythmia) is called tachyarrhythmia. Sepsis in Children will differentiate sinus node dysfunction Sinus node dysfunction A condition caused by dysfunctions related to the sinoatrial node including impulse generation (cardiac sinus arrest) and impulse conduction (sinoatrial exit block). It is characterized by persistent bradycardia, chronic atrial fibrillation, and failure to resume sinus rhythm following cardioversion. This syndrome can be congenital or acquired, particularly after surgical correction for heart defects. Bradyarrhythmias from AV block. A pacemaker Pacemaker A device designed to stimulate, by electric impulses, contraction of the heart muscles. It may be temporary (external) or permanent (internal or internal-external). Bradyarrhythmias is usually needed.
• Sinus bradycardia Sinus bradycardia Bradyarrhythmias: a sinus rhythm Sinus rhythm A heart rate and rhythm driven by the regular firing of the SA node (60–100 beats per minute) Cardiac Physiology with a heart rate Heart rate The number of times the heart ventricles contract per unit of time, usually per minute. Cardiac Physiology < 60 beats/min, which may result from vagal tone, medications, or underlying conditions. Symptoms can include dizziness Dizziness An imprecise term which may refer to a sense of spatial disorientation, motion of the environment, or lightheadedness. Lateral Medullary Syndrome (Wallenberg Syndrome), chest pain Pain An unpleasant sensation induced by noxious stimuli which are detected by nerve endings of nociceptive neurons. Pain: Types and Pathways, and 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. Electrocardiography Electrocardiography Recording of the moment-to-moment electromotive forces of the heart as projected onto various sites on the body’s surface, delineated as a scalar function of time. The recording is monitored by a tracing on slow moving chart paper or by observing it on a cardioscope, which is a cathode ray tube display. Electrocardiogram (ECG) shows a slow, regular Regular Insulin rhythm; narrow QRS complexes; and normal P wave P wave Electrocardiogram (ECG) morphology. Normal PR intervals and a lack of “dropped” beats differentiates sinus bradycardia Sinus bradycardia Bradyarrhythmias from AV block. Treatment depends on the patient’s stability and the underlying cause.