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Second Degree Atrioventricular Block

A second degree atrioventricular block is a cardiac abnormality causing normal atrioventricular (AV) conduction impairment. The impulse may be delayed or blocked inside the atrioventricular node or bundle. Depending on the severity of the condition, the patient may have no complaints or may less frequently, experience serious symptoms. This ailment is divided, based on electrocardiography findings, into Mobitz I and II types.


The people with Mobitz I second degree atrioventricular block can be divided into two categories. The first one is represented by trained athletes, with increased vagal tone, that have no symptoms and the heart block is an incidental finding. In their case, the prognosis is excellent. The second one is composed of individuals with underlying heart disease, that may experience dizziness, light-headedness, presyncope or syncope, due to cerebral hypotension. If the condition is due to myocardial ischemia or myocarditis, patients may experience angina. Additional findings include palpitations.

Furthermore, Mobitz II second degree atrioventricular block is more likely to progress to severe bradycardia and complete heart block [1], especially if associated with large anterior or inferior wall infarction. AV heart block is more often seen with inferior infarctions because in most cases the node is irrigated by the right coronary artery, as is the inferior heart wall. However, five-year survival has been shown to be reduced in unpaced Mobitz I patients compared to their healthy peers [2]. Asystole and sudden cardiac death risk are as high as 35% per year in Mobitz II individuals. Hemodynamic instability requires urgent intervention [3].

Transient Mobitz I block may occur after mitral valve surgery [4] or in cases with the Chagas disease after Valsalva maneuver [5].

Heart Disease
  • Abstract Paroxysmal atrial tachycardia with atrioventricular block usually indicates potentially dangerous overdigitalization, and serious heart disease is almost universally present.[ncbi.nlm.nih.gov]
  • The second one is composed of individuals with underlying heart disease, that may experience dizziness, light-headedness, presyncope or syncope, due to cerebral hypotension.[symptoma.com]
  • RESULTS: The average age of patients was 75 9 years; 99% were male; 59% had coronary heart disease; 44% had heart failure. 141 (47%) patients required CIED, of which 17 were implantable cardioverter-defibrillators (ICDs).[ncbi.nlm.nih.gov]
  • […] syncope, presyncope, and bradycardia in patients with heart disease.[emedicine.medscape.com]
  • Mobitz I second-degree AV block is localized to the AVN and thus is not associated with any increased risk of morbidity or death, in the absence of organic heart disease.[emedicine.medscape.com]


Beta-blockers and digoxin are known medications that reduce heart rate and may cause an atrioventricular block. Digoxin level determinations are widely available and should be used in individuals taking chronic treatment. Blood workup should also include an electrolyte, especially potassium, calcium and magnesium level determination. High potassium levels are a frequent cause of conduction impairment. Those who describe angina, especially if the pain is aggravated or suggestive for acute myocardial infarction, cardiac biomarkers should be urgently tested, since a block that appears in the context of an acute infarction is a poor prognosis factor. Myocarditis can be evaluated using echocardiography and serological markers, like enterovirus or adenovirus polymerase chain reaction, human immunodeficiency (HIV), and Lyme disease serologies, if available. Sarcoidosis needs to be excluded in the differential diagnosis [6]. In patients where congenital heart disease is a concern, thorough transthoracic or transesophageal echocardiography or computer tomography assessment should be performed. The latter is, however, reserved for situations where the first two methods offer incomplete information [7].

The main diagnostic tool for second degree atrioventricular block is the electrocardiogram. In Mobitz I, also known as Wenckebach block [1], the PR interval becomes progressively longer until a sinus impulse is blocked. PR interval is longest just before the dropped beat. In Mobitz II, the PR interval does not elongate, but blocked P waves occur. The R-R interval surrounding the blocked P wave measures exactly twice the preceding R-R interval if a single impulse is not conducted, or triple if two beats are dropped. The dropped beats will most often occur at regular intervals [3]. The block is named as a ratio of P waves to QRS complexes, for instance 3:2, 4:3, and so on [8]. In many cases, long electrocardiogram recordings are useful in order to correctly describe the pattern. The QRS complex may be narrow, but is often wide, due to intraventricular conduction abnormalities. A Mobitz II block is often infranodal, but may also be intranodal. A nodal location is suggested if the degree of the block improves with exercise. Infranodal blocks are improved by vagal maneuvers. The exact location of the pathological process is best described by electrophysiological methods, which is always indicated in patients with unexplained syncope.

Prolonged PR Interval
  • On the surface ECG this is realized through a prolonged PR interval.[ems12lead.com]
  • First-degree blocks are identifiable on ECG by a prolonged PR interval . Most patients with first-degree block are asymptomatic, and the condition is usually an incidental finding.[amboss.com]
  • Rate is not altered by the presence of the prolonged PR interval because it is still being controlled by the SA node.[cvphysiology.com]
  • ECGs that display a fixed 2:1 AV block cannot be easily classified; Wenckebach periodicity is suspected when the conducted P wave is associated with a borderline or prolonged PR interval and the QRS complex is narrow or when typical 3:2 AV conduction[doi.org]
  • A prolonged PR interval that results from a delay in the AV node's conduction of sinus impulses to the ventricle. All of the sinus impulses do get through; they just take longer than normal because the AV node is ischemic or otherwise suppressed.[quizlet.com]


  • RESULTS AND CONCLUSION: Although this patient's second-degree heart block may represent an intrinsic conduction abnormality unrelated to her AN, the importance of the validation of medical conditions during the treatment of AN is discussed.[ncbi.nlm.nih.gov]
  • Follow-up with periodical ECG is recommended for adult lupus patients to screen for possible conduction system involvement, and treatment should be started as soon as possible.[ncbi.nlm.nih.gov]
  • Our experience indicates that standard cardiovascular monitoring should be used for patients undergoing dental treatment under general anesthesia, even for young, healthy patients, to prevent and detect cardiovascular emergencies.[ncbi.nlm.nih.gov]
  • See Treatment and Medication for more detail.[emedicine.medscape.com]


  • CONCLUSION: The fetus with isolated congenital second degree atrioventricular block carries a good prognosis in the absence of maternal anti-SSA/Ro-SSB/La antibodies.[ncbi.nlm.nih.gov]
  • It is concluded that in the patients in the present study chronic Mobitz type I block has a similar prognosis to that of Mobitz type II block.[ncbi.nlm.nih.gov]
  • In their case, the prognosis is excellent. The second one is composed of individuals with underlying heart disease, that may experience dizziness, light-headedness, presyncope or syncope, due to cerebral hypotension.[symptoma.com]
  • The distinction between type II and type I block is descriptive; of greater importance to the clinician is the anatomic site of the block and the prognosis.[ncbi.nlm.nih.gov]
  • Prognosis The level of the block determines the prognosis.[emedicine.medscape.com]


  • Etiology Cardioactive drugs are an important cause of AV block. [9, 10, 11] They may exert negative (ie, dromotropic) effects on the AVN directly, indirectly via the autonomic nervous system, or both.[emedicine.medscape.com]
  • […] atrioventricular blocks Ischemic Heart Disease : accounts for 40% of cases of all atrioventricular blocks Drugs : most patients with atrioventricular block who are taking drugs that can impair conduction probably have underlying conduction system disease Etiology[mdnxs.com]
  • (First-degree heart block) Introduction Clinical definition an impairment of the electrical transmission from the atria to the ventricles Etiology idiopathic (most common) e.g., fibrosis and sclerosis of the conduction system ischemic heart disease (2nd[medbullets.com]


  • : occurs in younger patients (may be hereditary) Physiology : progressive, fibrotic, sclerodegenerative disease of the conduction system Clinical : frequently associated with slow progression to complete heart block Lev’s Disease Epidemiology : occurs[mdnxs.com]
  • Nevertheless, a true 2:1 AV block with possible primary pathology in the AVN and conduction system has also been reported in LQTS. [30] Epidemiology In the United States, the prevalence of second-degree AV block in young adults is reported to be 0.003%[emedicine.medscape.com]
Sex distribution
Age distribution


  • Thus, both "Mobitz type I" and "Wenckebach block" refer to the same pattern and pathophysiology.[en.wikipedia.org]
  • Pathophysiology Mobitz I second-degree AV block most often results from conduction disturbances in the AVN ( 70% of cases); however, in a minority of cases ( 30%), it may be due to infranodal block.[emedicine.medscape.com]
  • He authored his classic article on “partial block” of conduction between the atrium and ventricle in human hearts in 1924, commenting on their pathophysiological differences. 1 Between 1923 and 1930, Mobitz also published articles on congenital and acute[doi.org]


  • Although the patient was asymptomatic with ventricular pauses occurring only at night, it was decided to implant a permanent pacemaker to prevent neurological damage or life-threatening ventricular arrhythmias resulting from repeated, abnormally prolonged[ncbi.nlm.nih.gov]
  • Our experience indicates that standard cardiovascular monitoring should be used for patients undergoing dental treatment under general anesthesia, even for young, healthy patients, to prevent and detect cardiovascular emergencies.[ncbi.nlm.nih.gov]
  • CIEDs were implanted a median of 110 days after the ECG for symptomatic bradycardia, high-degree AV block or prevention of sudden cardiac death. Patients with CIED had greater cardiac co-morbidity than those without CIED.[ncbi.nlm.nih.gov]
  • Heart of the Matter LPN2007 , March/April 2007 Responding to Atrial Fibrillation Nursing2007 , April 2007 The Enduring Impact of Social Factors on Exercise Tolerance in Men Attending Cardiac Rehabilitation Journal of Cardiopulmonary Rehabilitation & Prevention[journals.lww.com]
  • .: Specific inhibitors and promoters of calcium action in the excitation-contraction coupling of heart muscle and their role in the prevention or production of myocardial lesions. In Calcium and the Heart, ed. ‎[books.google.es]



  1. Hayden GE, Brady WJ, Pollack M, et al. Electrocardiographic manifestations: Diagnosis of atrioventricular block in the emergency department. J Emerg Med. 2004;26(1):95–106.
  2. Shaw DB, Gowers JI, Kekwick CA, et al. Is Mobitz type I atrioventricular block benign in adults? Heart. 2004;90(2):169-74.
  3. Deal N. Evaluation and management of bradydysrhythmias in the emergency department. Emerg Med Pract. 2013;15(9):1–15.
  4. Meimoun P, Zeghdi R, D'Attelis N, et al. Frequency, predictors, and consequences of atrioventricular block after mitral valve repair. Am J Cardiol. 2002; 89:1062.
  5. Oliveira E, Ribeiro AL, Assis Silva F, et al. The Valsalva maneuver in Chagas disease patients without cardiopathy. Int J Cardiol. 2002; 82:49.
  6. Nery PB, Beanlands RS, Nair GM, et al. Atrioventricular block as the initial manifestation of cardiac sarcoidosis in middle-aged adults. Cardiovasc Electrophysiol. 2014;25(8):875-81.
  7. Takaoka H, Funabashi N, Ozawa K, et al. Computed tomography is important in appropriately diagnosing patients with third-degree atrioventricular block and second-degree atrioventricular block but not Wenckebach type. Int J Cardiol. 2017;228:700-6.
  8. Ufberg JW, Clark JS. Bradydysrhythmias and atrioventricular conduction blocks. Emerg Med Clin N Am. 2006;24(1):1–9.

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Last updated: 2018-06-21 17:32