First degree AV block

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sara Zand, M.D.[2] Mohammed Salih, M.D., Cafer Zorkun, M.D., Ph.D. [3], Ahmed Elsaiey, MBBCH [4]

First-degree AV block is a disease of the electrical conduction system of the heart in which the PR interval is prolonged. It is defined as PR prolongation of more than 200 milliseconds (normal PR interval is between 120 and 200 msec). First-degree AV block was first described by Dr. Engelmann in 1984. Dr. Ashmar further studied the blocked impulses and their impact on the conduction in the myocardium. The atrioventricular node is a normal electrical pathway between the atria and ventricles and it is located in the right atrium. First-degree AV block pathogenesis can be attributed to an electrical conduction delay in the AV node or His-Purkinje system. First-degree AV block can be associated with normal QRS complex or wide QRS complex on the ECG. It usually involves the atrioventricular node, but it can involve other structures. In first-degree AV block, all atrial impulses are conducted to the ventricles; however, there is a delay in conduction within the AV node resulting in a prolonged PR interval on ECG (>200 msec or >5 small blocks). In other words, a first-degree AV block is a slowed conduction without loss of atrioventricular synchrony. Common causes of first-degree AV block include ischemic heart disease, congenital heart disease, electrolyte abnormalities (particularly hypokalemia and hypomagnesemia), inflammation, infections (endocarditis, rheumatic fever, Chagas disease, Lyme disease, diphtheria), drugs (antiarrhythmic Ia, Ic, II, III, IV and digoxin, β-blockers, calcium channel blockers ), infiltrative diseases (sarcoidosis), collagen vascular diseases (SLE, rheumatoid arthritis, scleroderma), idiopathic degenerative diseases (Lenegre and Lev diseases) and neuromuscular disorders and increased vagal tone in younger patients. First-degree AV block should be differentiated from third-degree AV block, second degree AV block, supraventricular tachycardia with long PR. The prevalence of First-degree AV block is approximately 1000-2000 per 100,000 individuals in developed countries. The incidence of First-degree AV block was estimated to be 1000 cases per 100,000 in children and adolescent athletes and significantly lower than adults due to lower vagal tone in children. First-degree AV block is more commonly observed among elderly patients. Men are more commonly affected with first-degree AV block than women. The male to female ratio is approximately 2 to 1. First-degree AV block was more commonly observed among African-American subjects compared with Caucasian subjects. Common risk factors associated with atioventricular block include older age, male sex, history of myocardial infarction, history of congestive heart disease , high systolic blood pressure, increased fasting blood glucose level. Ambulatory electrocardiographic monitoring is useful for screening of intermittent atrioventricular block, LBBB and bifascicular block in asymptomatic patients. In patients with symptomatic atrioventricular block or bradycardia during sleep, screening about sleep apnea is recommended. Screening for congenital heart block is recommended in pregnant women with Ro/SSA antibodies. Women with history of neonatal lupus, fetal echos are recommended weekly or every other week from week 18 to 28. It is unclear how often first degree heart block progresses to complete heart block, some cases my revert to normal sinus rhythm or complete heart block.First-degree atrioventricular block may be due to conduction delay in the atrium, atrioventricular node, and/or His-Purkinje system. The atrioventricular node is the site most commonly involved in adults. However, more than 1 site of conduction delay is often present. Isolated First-degree atrioventricular has few clinical consequences. There are no symptoms or signs associated with it. First-degree AV block rarely progresses to more severe form of conduction abnormalities. In the setting of neuromuscular diseases such as myotonic dystrophy 1 with conduction abnormalities in the heart, First-degree AV block may progress to complete heart block during variable period of time. Common complications associated with first-degree heart block may include increased risk of atrial fibrillation, increased risk of pacemaker implantation. Prognosis of First degree AV block is generally good. However, some studies showed worse prognosis with PR prolongation. Presence of First degree AV block is shown to be associated with a higher risk of cardiovascular and all-cause mortality as well as higher risk of heart failure, left ventricular dysfunction, and atrial fibrillation. Symptoms related to atrioventricular block vary and related to the degree of atrioventricular block, the ventricular rate, and the frequency of its occurrence. Patients presented with First-degree AV block are usually asymptomatic. However, severe first-degree AV block may cause symptoms similar to pace maker syndrome including heart failure symptoms, exertional intolerance. Pseudo pacemaker syndrome is defined when the PR interval is >300ms leading to atrial contraction during the closed atrioventricular valves, loss of atrioventricular synchrony and decrease in cardiac output and an increase pulmonary capillary wedge pressure.First degree AV block may be an incidental finding on an routine ECG. General assessment about signs of underlying cardiac disease including auscultation for murmurs or additional heart sounds, assessment of JVD, peripheral edema, evaluation of skin about cyanosis, clubbing, or other signs of cardiac disease is warranted. There are no specific laboratory findings associated with First-degree AV block. However, in suspicion of underlying causes of atrioventricular block, laboratory testing about metabolic disorder, infectious disease, rheumatology disorder is reasonable. Echocardiography is useful for finding structural heart disease in patients with First-degree AV block while symptoms suspected to be cardiac in origin including syncope, presyncope, lightheadedness.In the presence of atrioventricular block and evidence of structural heart disease, cardiac imaging is considered. However, routine cardiac imaging is not recommended in patients with asymptomatic first-degree atrioventricular block and no clinical evidence of structural heart disease.The presence of severe first-degree atrioventricular block (PR >0.30 s) and a narrow QRS usually indicates atrioventricular node delay. However, ambulatory ECG monitoring is useful for finding the alternative changes in QRS morphology. In addition, exercise stress test can be used to identify the ischemia as the precursor of the development of atrioventricular block.Commonly, there is no need for treating first-degree AV block. Permanent pacemaker indicates only for symptomatic first-degree AV block with PR>300 ms,neuromuscular disease, or in presence of wide QRS compelex. First-degree AV block in the setting of acute myocardial infarction usually reverses after recovery from acute phase of myocardial infarction. Antiarrhythmic medications should be avoided in first-degreeAV block.Common factors associated with placement of permanent pacemaker include presence or absence of symptoms, level of atrioventricular block, unstable scaped ventricular rhythm with rapid progression to complete heart block. First-degree AV block is typically a benign condition that do not progress suddenly to complete heart block. Placement of permanent pacemaker is reserved for the condition that symptomatic First-degree AV block affects quality of life as well as evidence of atrioventricular block in neurologic conditions with Lamin A/C mutation ( limb girdle, emery dreifuss, muscular dystrophies). Effective measures for primary prevention of atrioventricular block include treatment of hypertension and maintenance of normal blood glucose levels. There are no established measures for the secondary prevention of first-degree heart block.

First-degree AV block was first described by Dr. Engelmann in 1984. Dr. Ashmar further studied the blocked impulses and their impact on the conduction in the myocardium.

There is no established system for the classification of First degree AV block.

The atrioventricular node is a normal electrical pathway between the atria and ventricles and it is located in the right atrium. First-degree AV block pathogenesis can be attributed to an electrical conduction delay in the AV node or His-Purkinje system. First-degree AV block can be associated with normal QRS complex or wide QRS complex on the ECG.

Common causes of first-degree AV block include ischemic heart disease, congenital heart disease, electrolyte abnormalities (particularly hypokalemia and hypomagnesemia), inflammation, infections (endocarditis, rheumatic fever, Chagas disease, Lyme disease, diphtheria), drugs (antiarrhythmic Ia, Ic, II, III, IV and digoxin, β-blockers, calcium channel blockers ), infiltrative diseases (sarcoidosis), collagen vascular diseases (SLE, rheumatoid arthritis, scleroderma), idiopathic degenerative diseases (Lenegre and Lev diseases) and neuromuscular disorders and increased vagal tone in younger patients.

First-degree AV block should be differentiated from [[third-degree AV block], second degree AV block, supraventricular tachycardia with long PR.

The prevalence of First-degree AV block is approximately 1000-2000 per 100,000 individuals in developed countries. The incidence of First-degree AV block was estimated to be 1000 cases per 100,000 in children and adolescent athletes and significantly lower than adults due to lower vagal tone in children. First-degree AV block is more commonly observed among elderly patients. Men are more commonly affected with first-degree AV block than women. The male to female ratio is approximately 2 to 1. First-degree AV block was more commonly observed among African-American subjects compared with Caucasian subjects.

Common risk factors associated with atioventricular block include older age, male sex, history of myocardial infarction, history of congestive heart disease , high systolic blood pressure, increased fasting blood glucose level.

Ambulatory electrocardiographic monitoring is useful for screening of intermittent atrioventricular block, LBBB and bifascicular block in asymptomatic patients. In patients with symptomatic atrioventricular block or bradycardia during sleep, screening about sleep apnea is recommended. Screening for congenital complete heart block is recommended in pregnant women with Ro/SSA antibodies. Women with history of neonatal lupus, fetal echos are recommended weekly or every other week from week 18 to 28. It is unclear how often first degree heart block progresses to complete heart block, some cases my revert to normal sinus rhythm or complete heart block.

First-degree atrioventricular block may be due to conduction delay in the atrium, atrioventricular node, and/or His-Purkinje system. The atrioventricular node is the site most commonly involved in adults. However, more than 1 site of conduction delay is often present. Isolated First-degree atrioventricular has few clinical consequences. There are no symptoms or signs associated with it. First-degree AV block rarely progresses to more severe form of conduction abnormalities. In the setting of neuromuscular diseases such as myotonic dystrophy 1 with conduction abnormalities in the heart, First-degree AV block may progress to complete heart block during variable period of time. Common complications associated with first-degree heart block may include increased risk of atrial fibrillation, increased risk of pacemaker implantation. Prognosis of First degree AV block is generally good. However, some studies showed worse prognosis with PR prolongation. Presence of First degree AV block is shown to be associated with a higher risk of cardiovascular and all-cause mortality as well as higher risk of heart failure, left ventricular dysfunction, and atrial fibrillation.

Symptoms related to atrioventricular block vary and related to the degree of atrioventricular block, the ventricular rate, and the frequency of its occurrence. Patients presented with First-degree AV block are usually asymptomatic. However, severe first-degree AV block may cause symptoms similar to pace maker syndrome including heart failure symptoms, exertional intolerance. Pseudo pacemaker syndrome is defined when the PR interval is >300ms leading to atrial contraction during the closed atrioventricular valves, loss of atrioventricular synchrony and decrease in cardiac output and an increase pulmonary capillary wedge pressure.

First degree AV block may be an incidental finding on an routine ECG. General assessment about signs of underlying cardiac disease including auscultation for murmurs or additional heart sounds, assessment of JVD, peripheral edema, evaluation of skin about cyanosis, clubbing, or other signs of cardiac disease is warranted.

There are no specific laboratory findings associated with First-degree AV block. However, in suspicion of underlying causes of atrioventricular block, laboratory testing about metabolic disorder, infectious disease, rheumatology disorder is reasonable.

In normal individuals, the AV node slows the conduction of electrical impulse through the heart. This is manifest on a surface EKG as the PR interval. The normal PR interval is from 120 milliseconds (ms) to 200 milliseconds (ms) in duration. This is measured from the initial deflection of the P wave to the beginning of the QRS complex.

In first degree heart block, the diseased AV node conducts the electrical activity slower. This is seen as a PR interval greater than 200 milliseconds (ms) in length on the surface EKG. It is usually an incidental finding on a routine EKG.

First degree heart block does not require any particular evaluation except for electrolyte and drug screens especially if an overdose is suspected.

There are no x-ray findings associated with first degree AV block.

Echocardiography is useful for finding structural heart disease in patients with First-degree AV block while symptoms suspected to be cardiac in origin including syncope, presyncope, lightheadedness.

In the presence of atrioventricular block and evidence of structural heart disease, cardiac imaging is considered. However, routine cardiac imaging is not recommended in patients with asymptomatic first-degree atrioventricular block and no clinical evidence of structural heart disease.

The presence of severe first-degree atrioventricular block (PR >0.30 s) and a narrow QRS usually indicates atrioventricular node delay. However, ambulatory ECG monitoring is useful for finding the alternative changes in QRS morphology. In addition, exercise stress test can be used to identify the ischemia as the precursor of the development of atrioventricular block.

Commonly, there is no need for treating first-degree AV block. Permanent pacemaker indicates only for symptomatic first-degree AV block with PR>300 ms,neuromuscular disease, or in presence of wide QRS compelex. First-degree AV block in the setting of acute myocardial infarction usually reverses after recovery from acute phase of myocardial infarction. Antiarrhythmic medications should be avoided in first-degreeAV block.

Common factors associated with placement of permanent pacemaker include presence of symptoms, level of atrioventricular block, unstable scaped ventricular rhythm with rapid progression to complete heart block. First-degree AV block is typically a benign condition that do not progress suddenly to complete heart block. Placement of permanent pacemaker is reserved for the condition that symptomatic First-degree AV block affects quality of life as well as evidence of atrioventricular block in neurologic conditions with Lamin A/C mutation ( limb girdle, emery dreifuss, muscular dystrophies).

Effective measures for primary prevention of atrioventricular block include treatment of hypertension and maintenance of normal blood glucose levels

There are no established measures for the secondary prevention of first-degree heart block.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ahmed Elsaiey, MBBCH [2]

First-degree AV block was first described by Dr. Engelmann in 1984. Dr. Ashmar further studied the blocked impulses and their impact on the conduction in the myocardium.

• In 1894, Dr. Engelmann described a phenomenon of AV interval lengthening. Dr. Engelmann described a stimulus that is applied to the atrium followed by elongation of the AV interval.^[1]
• In 1925, Dr. Ashmar further studied these blocked impulses and their impact on the conduction in the muscle of the heart.
• Dr. Ashmar stated the early blocked beats that follow normal impulses have less effect on the conduction system.

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mohammed Salih, M.D., Ahmed Elsaiey, MBBCH [2], Cafer Zorkun, M.D., Ph.D. [3]

The atrioventricular node is a normal electrical pathway between the atria and ventricles and it is located in the right atrium. First-degree AV block pathogenesis can be attributed to an electrical conduction delay in the AV node or His-Purkinje system. First-degree AV block can be associated with normal QRS complex or wide QRS complex on the ECG.

• The atrioventricluar node is the normal electrical pathway between the atria and ventricles. It is located in the right atrium near to the tricuspid valve leaflet.
• The AV node receives blood supply from the right coronary artery in most of the population.
• The bundle of His is the electrical connection between the AV node to the interventricular septum. At the end of the septum, a bundle of His is divided into the right and left bundle branches to the ventricular walls.

• First-degree AV block broadly means the prolongation of the PR interval on the ECG with normal atrioventricular node function.
• First-degree AV block pathogenesis can be attributed to an electrical conduction delay in one of the following:^[1]
  • Atrioventricular node
  • His-Purkinje system which is formed of both bundle of His and Purkinje fibers
• The conduction delay can be also in both the AV node and His-Purkinje system.
• One of the characteristics of first-degree AV block is that there are no beats skipped and it has a regular rhythm.

First-degree AV block with normal QRS duration results from atrial or AV nodal delay.

First-degree AV block with wide QRS complex most often results from delay in conduction in the bundle of His and in some patients, the AV node.

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Cafer Zorkun, M.D., Ph.D. [2]; Raviteja Guddeti, M.B.B.S. [3]

Common causes of first-degree AV block include ischemic heart disease, congenital heart disease, electrolyte abnormalities (particularly hypokalemia and hypomagnesemia), inflammation, infections (endocarditis, rheumatic fever, Chagas disease, Lyme disease, diphtheria), drugs (antiarrhythmic Ia, Ic, II, III, IV and digoxin, β-blockers, calcium channel blockers ), infiltrative diseases (sarcoidosis), collagen vascular diseases (SLE, rheumatoid arthritis, scleroderma), idiopathic degenerative diseases (Lenegre and Lev diseases) and neuromuscular disorders and increased vagal tone in younger patients.

Life-threatening causes include conditions which may result in death or permanent disability within 24 hours if left untreated.

• Acute myocardial infarction
• Acute rheumatic fever
• Bacterial endocarditis
• Myocarditis

• Hyperkalemia
• Hyperthyroidism
• Hypothyroidism
• Increased vagal tone (e.g. sleep, athletes)
• Ischemic heart disease
• Medications ( e.g. adenosine, amiodarone, beta-blockers, diltiazem, procainamide, verapamil)

Cardiovascular	Acute myocardial infarction, acute rheumatic fever, ASD, dilated cardiomyopathy, Ebstein’s anomaly, hypersensitive carotid sinus syndrome, hypertension, hypertrophic cardiomyopathy, Lev’s disease, myocardial bridging, myocarditis, post aortic valve replacement, post catheter ablation for arrhythmias, post closure of a ventricular septal defect, post mitral valve replacement, tetralogy of Fallot, endocardial cushion defect, transposition of the great vessels, valvular heart disease, VSD
Chemical / poisoning	No underlying causes
Dermatologic	No underlying causes
Drug Side Effect	Amiodarone, beta-blockers, digitalis, calcium channel blockers, cholinesterase inhibitors, disopyramide, dofetilide, dolasetron, donepezil, eslicarbazepine acetate, fesoterodine, fingolimod, flecainide, ibutilide, lacosamide, magnesium, paliperidone, pramipexole, procainamide, propafenone, propoxyphene, quinidine, sotalol, terodiline
Ear Nose Throat	No underlying causes
Endocrine	Hyperthyroidism, myxedema, thyrotoxic periodic paralysis, hypothyroidism
Environmental	Hypothermia
Gastroenterologic	Hemochromatosis
Genetic	Emery-Dreifuss muscular dystrophy, Fabry disease, glycogenosis type 2b, hereditary neuromuscular disease, Kearns-Sayre syndrome
Hematologic	Multiple myeloma
Iatrogenic	Post aortic valve replacement, post catheter ablation for arrhythmias, post closure of a ventricular septal defect, post mitral valve replacement
Infectious Disease	Acute rheumatic fever, Chagas disease, diphtheria, Lyme disease, myocarditis, neonatal lupus erythematosus, protozoal infection, sarcoidosis, SLE, tuberculosis
Musculoskeletal / Ortho	Ankylosing spondylitis, hereditary neuromuscular disease, Kearns-Sayre syndrome, mitochondrial genome inherited conditions, muscular dystrophy
Neurologic	No underlying causes
Nutritional / Metabolic	Fabry disease, glycogenosis type 2b
Obstetric/Gynecologic	No underlying causes
Oncologic	Multiple myeloma
Opthalmologic	No underlying causes
Overdose / Toxicity	No underlying causes
Psychiatric	No underlying causes
Pulmonary	Sarcoidosis
Renal / Electrolyte	Hyperkalemia, hypokalemia
Rheum / Immune / Allergy	Ankylosing spondylitis, dermatomyositis, rheumatoid arthritis, scleroderma, SLE
Sexual	No underlying causes
Trauma	No underlying causes
Urologic	No underlying causes
Dental	No underlying causes
Miscellaneous	Amyloidosis, degenerative diseases, enhanced vagal tone, normal variants

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Raviteja Guddeti, M.B.B.S. [2]

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First-degree AV block should be differentiated from [[third-degree AV block], second degree AV block, supraventricular tachycardia with long PR.

First-degree AV block should be differentiated from the following:

• Third-degree AV block
• Second degree AV block
• Supraventricular tachycardia with long PR

following table summarizes the differential diagnosis of First-degree AV block:

Arrhythmia		Rhythm	Rate	P wave	PR Interval	QRS Complex	Response to Maneuvers	Epidemiology	Co-existing Conditions
Atrioventricular block[1]	First degree [2][3]	Regular		Normal	Prolonged PR interval (>200 msec)	Less than 0.12 seconds, consistent, and normal in morphology.	No treatment required	Prevalence: 650 to 1600 per 100,000 individuals in the united states.	Heart failure Coronary heart disease Cardiomyopathy Sarcoidosis Lyme disease Defenerative muscle disorders as Lev’s disease and Lenegre’s disease. Overly active vagus nerve.
	Second degree[4][5]	Regular irregular		Normal	Mobtiz I: Progressive PR prolongation Mobitz II: Normal PR interval	QRS is normal but dropped as the following: Mobitz I: QRS complex is dropped after a progressive lengthening of PR Mobitz II: QRS complex is dropped after a normal PR	Can be reversed by using a pacemaker.	Prevalence: 3 per 100,000 individuals in the united states.
	Third degree[6][7]	Regular		Normal but no relationship between P wave and the QRS. More P waves than the QRS complexes.	Varies	Normal QRS	Can be reversed by using a pacemaker.	The prevalence: 20 per 100,000 individuals worldwide.
Atrial Fibrillation (AFib)[8][9]		Irregularly irregular	On a 10-second 12-lead EKG strip, multiply number of QRS complexes by 6	Absent Fibrillatory waves	Absent	Less than 0.12 seconds, consistent, and normal in morphology in the absence of aberrant conduction	Does not break with adenosine or vagal maneuvers	2.7–6.1 million people in the United States have AFib 2% of people younger than age 65 have AFib, while about 9% of people aged 65 years or older have AFib	Elderly Following bypass surgery Mitral valve disease Hyperthyroidism Diabetes Heart failure Ischemic heart disease Chronic kidney disease Heavy alcohol use Left chamber enlargement
Atrial Flutter[10]		Regular or Irregular	75 (4:1 block), 100 (3:1 block) and 150 (2:1 block) beats per minute (bpm), but 150 is more common	Sawtooth pattern of P waves at 250 to 350 bpm Biphasic deflection in V1	Varies depending upon the magnitude of the block, but is short	Less than 0.12 seconds, consistent, and normal in morphology	Conduction may vary in response to drugs and maneuvers dropping the rate from 150 to 100 or to 75 bpm	Incidence: 88 per 100,000 individuals	Elderly Alcohol
Atrioventricular nodal reentry tachycardia (AVNRT)[11][12][13][14]		Regular	140-280 bpm	Slow-Fast AVNRT: Pseudo-S wave in leads II, III, and AVF Pseudo-R’ in lead V1. Fast-Slow AVNRT P waves between the QRS and T waves (QRS-P-T complexes) Slow-Slow AVNRT Late P waves after a QRS Often appears as atrial tachycardia. Inverted, superimposed on or buried within the QRS complex (pseudo R prime in V1/pseudo S wave in inferior leads)	Absent (P wave can appear after the QRS complex and before the T wave, and in atypical AVNRT, the P wave can appear just before the QRS complex)	Less than 0.12 seconds, consistent, and normal in morphology in the absence of aberrant conduction QRS alternans may be present	May break with adenosine or vagal maneuvers	60%-70% of all supraventricular tachycardias	Structural heart disease Atrial tachyarrhythmias
Multifocal Atrial Tachycardia[15][16]		Irregular	Atrial rate is > 100 beats per minute	Varying morphology from at least three different foci Absence of one dominant atrial pacemaker, can be mistaken for atrial fibrillation if the P waves are of low amplitude	Variable PR intervals, RR intervals, and PP intervals	Less than 0.12 seconds, consistent, and normal in morphology	Does not terminate with adenosine or vagal maneuvers	0.05% to 0.32% of electrocardiograms in general hospital admissions	Elderly Chronic obstructive pulmonary disease (COPD)
Paroxysmal Supraventricular Tachycardia		Regular	150 and 240 bpm	Absent Hidden in QRS	Absent	Narrow complexes (< 0.12 s)	Breaks with vagal maneuvers, adenosine, diving reflex, oculocardiac reflex	Prevalence: 0.023 per 100,000	Alcohol Caffeine Nicotine Psychological stress Wolff-Parkinson-White syndrome
Premature Atrial Contractrions (PAC)[17][18]		Regular except when disturbed by premature beat(s)	80-120 bpm	Upright	> 0.12 second Maybe shorter than that in normal sinus rhythm (NSR) if the origin of PAC is located closer to the AV node Ashman’s Phenomenon: PAC displaying a right bundle branch block pattern	Usually narrow (< 0.12 s)	Breaks with vagal maneuvers, adenosine, diving reflex, oculocardiac reflex		Infants Cardiomyopathy Myocarditis Elderly Coronary artery disease Stroke Increased atrial natriuretic peptide (ANP) Hypercholesterolemia
Wolff-Parkinson-White Syndrome[19][20]		Regular	Atrial rate is nearly 300 bpm and ventricular rate is at 150 bpm	With orthodromic conduction due to a bypass tract, the P wave generally follows the QRS complex, whereas in AVNRT, the P wave is generally buried in the QRS complex.	Less than 0.12 seconds	A delta wave and evidence of ventricular pre-excitation if there is conduction to the ventricle via ante-grade conduction down an accessory pathway A delta wave and pre-excitation may not be present because bypass tracts do not conduct ante-grade.	May break in response to procainamide, adenosine, vagal maneuvers	Worldwide prevalence of WPW syndrome is 100 – 300 per 100,000	Ebstein’s anomaly Mitral valve prolapse: This cardiac disorder, if present, is associated with left-sided accessory pathways. Hypertrophic cardiomyopathy: This disorder is associated with familial/inherited form of WPW syndrome. Hypokalemic periodic paralysis Pompe disease Tuberous sclerosis
Ventricular Fibrillation (VF)[21][22][23]		Irregular	150 to 500 bpm	Absent	Absent	Absent (R on T phenomenon in the setting of ischemia)	Does not break in response to adenosine, vagal maneuvers	3-12% cases of acute myocardial infarction (AMI) Out of 356,500 out of hospital cardiac arrests, 23% have VF as initial rhythm	Myocardial ischemia / infarction Cardiomyopathy Channelopathies e.g. Long QT (acquired / congenital) Electrolyte abnormalities (hypokalemia/hyperkalemia, hypomagnesemia) Aortic stenosis Aortic dissection Myocarditis Cardiac tamponade Blunt trauma (Commotio Cordis) Sepsis Hypothermia Pneumothorax Seizures Stroke
Ventricular Tachycardia[24][25]		Regular	> 100 bpm (150-200 bpm common)	Absent	Absent Initial R wave in V1, initial r > 40 ms in V1/V2, notched S in V1, initial R in aVR, lead II R wave peak time ≥50 ms, no RS in V1-V6, and atrioventricular dissociation	Wide complex, QRS duration > 120 milliseconds	Does not break in response to adenosine, vagal maneuvers	5-10% of patients presenting with AMI	Coronary artery disease Aortic stenosis Cardiomyopathy Electrolyte imbalances (e.g., hypokalemia, hypomagnesemia) Inherited channelopathies (e.g., long-QT syndrome) Catecholaminergic polymorphic ventricular tachycardia Arrhythmogenic right ventricular dysplasia Myocardial infarction Torsades de pointes is a form of polymorphic VT that is often associated with a prolonged QT interval

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sara Zand, M.D.[2] Ahmed Elsaiey, MBBCH [3], Cafer Zorkun, M.D., Ph.D. [4]

The prevalence of First-degree AV block is approximately 1000-2000 per 100,000 individuals in developed countries. The incidence of First-degree AV block was estimated to be 1000 cases per 100,000 in children and adolescent athletes and significantly lower than adults due to lower vagal tone in children. First-degree AV block is more commonly observed among elderly patients. Men are more commonly affected with first-degree AV block than women. The male to female ratio is approximately 2 to 1. First-degree AV block was more commonly observed among African-American subjects compared with Caucasian subjects.

• The prevalence of First-degree AV block is approximately 1000-2000 per 100,000 individuals in developed countries.^[1]
• The incidence of First-degree AV block was estimated to be 1000 cases per 100,000 in children and adolescent athletes and significantly lower than adult due to lower vagal tone.^[2]

• First-degree AV block is more commonly observed among elderly patients.

• Men are more commonly affected with first-degree AV block than women .
• The male to female ratio is approximately 2 to 1.

• First-degree AV block was more commonly observed among African-American subjects compared with Caucasian subjects.^[3]

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sara Zand, M.D.[2] Ahmed Elsaiey, MBBCH [3]

Common risk factors associated with atioventricular block include older age, male sex, history of myocardial infarction, history of congestive heart disease , high systolic blood pressure, increased fasting blood glucose level.

• Common risk factors associated with atioventricular block include:^[1]

• Older age
• Male sex
• History of myocardial infarction
• History of congestive heart disease
• High systolic blood pressure
• Increased fasting blood glucose level

• Common risk factors associated with atrioventricular block after cardiac surgery include:

• Older age
• Atrial fibrillation
• Prior surgery
• Preoperative renal failure
• Active endocarditis

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sara Zand, M.D.[2] Ahmed Elsaiey, MBBCH [3]

Ambulatory electrocardiographic monitoring is useful for detection of intermittent atrioventricular block, LBBB and bifascicular block in asymptomatic patients. In patients with symptomatic atrioventricular block or bradycardia during sleep, screening about sleep apnea is recommended. Screening for congenital complete heart block is recommended in pregnant women with Ro/SSA antibodies. Women with history of neonatal lupus, fetal echos are recommended weekly or every other week from week 18 to 28. It is unclear how often first degree heart block progresses to complete heart block, some cases my revert to normal sinus rhythm or complete heart block.

• Ambulatory electrocardiographic monitoring is useful for detection of intermittent atrioventricular block, LBBB and bifascicular block in asymptomatic patients.
• In patients with symptomatic atrioventricular block or bradycardia during sleep, screening about sleep apnea is recommended.^[1]
• Screening for congenital complete heart block is recommended in pregnant women with Ro/SSA antibodies.^[2]
• Women with history of neonatal lupus, fetal echos are recommended weekly or every other week from week 18 to 28.
• It is unclear how often first degree heart block progresses to complete heart block, some cases my revert to normal sinus rhythm or complete heart block.

Recommendations for screening sleep apnea in patients with bradycardia or conduction disorder

(Class I, Level of Evidence B):

❑ Screening about sleep apnea syndrome is recommended In patients with documented or suspected bradycardia or conduction disorder during sleep ❑ Continuous airway pressure and weight loss is recommended in patients with bradycardia or conduction disorder during sleep and documented obstructive sleep apnea

(Class IIa, Level of Evidence B):

❑ In patients with previously PPM implantation for bradycardia or conduction disorder, screening about sleep apnea syndrome is reasonable

The above table adopted from 2018 AHA/ACC/HRS Guideline[3]

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Sara Zand, M.D.[2] Cafer Zorkun, M.D., Ph.D. [3]

First-degree atrioventricular block may be due to conduction delay in the atrium, atrioventricular node, and/or His-Purkinje system. The atrioventricular node is the site most commonly involved in adults. However, more than 1 site of conduction delay is often present. Isolated First-degree atrioventricular has few clinical consequences. There are no symptoms or signs associated with it. First-degree AV block rarely progresses to more severe form of conduction abnormalities. In the setting of neuromuscular diseases such as myotonic dystrophy 1 with conduction abnormalities in the heart, First-degree AV block may progress to complete heart block during variable period of time. Common complications associated with first-degree heart block may include increased risk of atrial fibrillation, increased risk of pacemaker implantation. Prognosis of First degree AV block is generally good. However, some studies showed worse prognosis with PR prolongation. Presence of First degree AV block is shown to be associated with a higher risk of cardiovascular and all-cause mortality as well as higher risk of heart failure, left ventricular dysfunction, and atrial fibrillation.

• First-degree atrioventricular block may be due to conduction delay in the atrium, atrioventricular node, and/or His-Purkinje system
• The atrioventricular node is the site most commonly involved in adults. However, more than 1 site of conduction delay is often present.
• Isolated first-degree atrioventricular has few clinical consequences. There are no symptoms or signs associated with it.
  • First-degree AV block rarely progresses to more severe form of conduction abnormalities, it is mostly a benign condition in healthy middle-aged men and is not correlated with coronary heart disease.^[1]
• In the setting of neuromuscular diseases such as myotonic dystrophy 1 with conduction abnormalities in the heart, First-degree AV block may progress to complete heart block during variable period of time.

Common complications associated with first-degree heart block may include the following: ^[2]

• Increased risk of atrial fibrillation
• Increased risk of Pacemaker implantation

  Individuals who have the First-degree block as part of a triad of First-degree heart block, right bundle branch block, and either left anterior fascicular block or left posterior fascicular block (known as trifascicular block) may be at an increased risk of progression to complete heart block.

• Prognosis of first degree AV block is generally good^[3]. However, some studies showed worse prognosis with PR prolongation.^[4]
• Presence of first degree AV block is shown to be associated with a higher risk of cardiovascular and all-cause mortality.^[5]

• In a 2016 meta-analysis, first degree AV block was found to be associated with higher mortality risk. It was also associated with a high risk of heart failure, left ventricular dysfunction, and atrial fibrillation. However, it was not associated with high risk of coronary artery disease, stroke, or myocardial infarction.^[6]

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