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Sinoatrial Block

Blocks Sinoatrial

Sinoatrial block, also known as sinoatrial exit block, is a cardiac abnormality in which inability of the heart to conduct impulses from the sinoatrial node leads to a range of arrhythmias and associated symptoms. The diagnosis rests on clinical findings and electrocardiography.


Sinoatrial (SA) block is one of the forms of sinus node dysfunction (SND), and its main pathological entities, bradycardia (and less commonly tachycardia) cause low cardiac output and the appearance of various symptoms [1] [2] [3]. Patients can be asymptomatic for a prolonged period of time, but the unpredictable and often sudden appearance of dizziness, palpitations, vertigo and syncope without an identifiable cause are main clinical manifestations of SA block [4] [5]. Angina, dyspnea, fatigue, lethargy and premature mental incapacity may point to initial stages of congestive heart failure, which may occur in the setting of profound arrhythmias [4]. In addition to bradycardia, numerous forms of tachyarrhythmia appear in diseases of the SA node, including SA block, most common entities being supraventricular tachycardias - atrial flutter and atrial fibrillation [6]. In fact, tachycardia seems to be responsible for the onset of palpitations and heart failure, whereas hypotension, syncope, and weakness arise due to bradycardia [6]. Paradoxically, atrial fibrillation can reduce the burden of symptoms in patients with persistent bradycardia, as it directly increases heart rate [6]. In rare cases, cardiac arrest and death have been noted, while other generalised symptoms include slurred speech, irritability, and poor infant feeding.

Heart Disease
  • Twenty-one patients had organic heart disease; in the remaining ten signs of underlying heart disease were not present. Nineteen patients had dizziness or syncope.[ncbi.nlm.nih.gov]
  • Analysis of the survival curves shows that the excess mortality is caused by coexisting diseases, primarily coronary heart disease with previous myocardial infarction and valvular heart disease.[ncbi.nlm.nih.gov]
  • […] series, 4 all patients had advanced heart disease, although were also on digitalis therapy, which is known to increase the parasympathetic activity.[academic.oup.com]
  • However, it always interferes with using an electrocardiogram to diagnose heart disease. Causes and Risk Factors Bundle branch block is a common disorder. It occurs in many medical conditions.[cedars-sinai.edu]
  • These medical conditions include: Heart failure Prior heart attack Heart valve abnormalities Heart valve surgery Congenital heart diseases Some medications or exposure to toxic substances Lyme disease Aging[hrsonline.org]


A thorough patient history and a detailed physical examination are essential steps in making an initial diagnosis of an SA block. Severe bradycardia or other rhythm abnormalities, weak arterial pulses and hypotension can be observed during cardiac auscultation. When such findings are documented, electrocardiography (ECG) studies should be done. On the basis of ECG findings, SA block is classified into four subtypes [2] [3] [5] [6]:

  • Type 1 - Minimal prolongation of the SA node may either present with a normal ECG (1st-degree) or with intermittent failure of impulse conduction to the arterioventricular (AV) node (2nd-degree), manifesting as an occasional absence of P waves.
  • Type 2 - In 1st-degree type 2 SA block (also known as Wenckebach block), slowing of the impulse is noted before the onset of a blockade, which is seen on ECG as a decreasing P-P interval that ultimately causes joining of two P waves and a consequent pause. In 2nd-degree type 2 block, on the other hand, SA impulse blocks occur without slowing, but the pause is much greater and the appearance of grouped beats may be detected.
  • Type 3 - The definite absence of P waves, also known as sinus arrest, is the main feature of a complete SA block.

Because SA blocks present with various ECG manifestations, use of devices that ensure long-term monitoring of cardiac impulse conduction, as well as exercise testing and intracardiac electrophysiologic tests, are recommended when valid clinical criteria exist [2].

Legionella Pneumophila
  • Her urine tested positive for Legionella pneumophila antigen serotype 1 and she improved with antibiotic therapy.[ncbi.nlm.nih.gov]
Prolonged PR Interval
  • This is different than a first-degree atrioventricular, or AV, block, which shows a prolonged PR interval. Second-degree sinoatrial exit block is categorized into type I and type II.[healio.com]
Sinus Arrest
  • A third degree sinoatrial block looks very similar to a sinus arrest. However, a sinus arrest is caused by a failure to form impulses. A third degree block is caused by failure to conduct them. The rhythm is irregular and either normal or slow.[en.wikipedia.org]
  • SA exit block, Sinus Arrest, AV Blocks and Escape Rhythms ECG EXERCISE 28.[slideshare.net]
  • The onset of 3rd degree SA block may produce long sinus pauses or sinus arrest (may lead to fatal asystole). Rhythm may be maintained by a junctional escape rhythm.[lifeinthefastlane.com]
  • Type 3 - The definite absence of P waves, also known as sinus arrest, is the main feature of a complete SA block.[symptoma.com]
  • SA block is included in a broader clinical scenario called “sick sinus syndrome” (SSS) that may consist in inappropriate sinus bradycardia, SA exit block or sinus arrest, prolonged sinus arrest with failing ectopic pacemaker, persistent atrial or atrioventricular[link.springer.com]


  • The correlation between lithium treatment and tachyarrhythmias is discussed.[ncbi.nlm.nih.gov]
  • On diagnosing SAHS with an obstructive component in patients with symptomatic bradycardia and SA block, there is no primary need for a pacemaker, but rather for implementing treatment with nCPAP.[ncbi.nlm.nih.gov]
  • Symptoms and treatment [ edit ] Sinoatrial blocks are typically well-tolerated. They are not as serious as an AV block and most often do not require treatment.[en.wikipedia.org]
  • Sinus node modification with radiofrequency current has been used successfully as treatment for this arrhythmia. However, the electrophysiologic mechanisms leading to successful modification are not yet fully elucidated.[ncbi.nlm.nih.gov]
  • All of these abnormalities resolved completely after antithyroid treatment. This course of events illustrates the profound effect of thyroid hormones on cardiac function.[ncbi.nlm.nih.gov]


  • Overall, the prognosis is favorable.[emedicine.medscape.com]
  • Thus, the occurrence of block W during the daytime activity may be evidence of a maintained autonomic balance that signifies both the presence of a structural disease of the sinus node and a better prognosis.[academic.oup.com]


  • Etiology SA block is uncommon and usually occurs transiently may occur in healthy patients with increased vagal tone or with vagal stimulation found with CAD, inferior MI, myocarditis, heart failure, or disease of SA node contributing medications (digoxin[ecgreview.weebly.com]
  • Etiology Atrioventricular (AV) block results from various pathologic states that cause infiltration, fibrosis, or loss of connection in portions of the healthy conduction system.[emedicine.medscape.com]
  • Etiology of sinus pauses and arrest: alteration in the impulse rate of the P cells. Therefore, the pause length is variable and not necessarily a multiple of the basic sinus rate.[hqmeded-ecg.blogspot.com]


  • Epidemiology In the United States, the prevalence of third-degree atrioventricular (AV) block (complete heart block) is 0.02%.[emedicine.medscape.com]
Sex distribution
Age distribution


  • Pathophysiology In the heart, normal impulse initiation begins in the sinoatrial node (SAN). The excitation wave then travels through the atrium. During this time, surface electrocardiographic (ECG) recordings show the P wave.[emedicine.medscape.com]
  • Despite these limitations, a suggested relation of block W during both daytime activity and sleep with an improved survival, most likely through the autonomic link, may give some additional insight into the pathophysiology of the sinoatrial Wenckebach[academic.oup.com]


  • Bier block regional anesthesia by intravenous injection, used for surgical procedures on the forearm or the lower leg; performed in a bloodless field maintained by a pneumatic tourniquet that also prevents anesthetic from entering the systemic circulation[medical-dictionary.thefreedictionary.com]
  • Corrado D, Pelliccia A, Heidbuchel H et al (2010) Section of Sports Cardiology, European Association of Cardiovascular Prevention and Rehabilitation. Recommendations for interpretation of 12-lead electrocardiogram in the athlete.[link.springer.com]
  • The National Heart, Lung, and Blood Institute (NHLBI) leads or sponsors many studies aimed at preventing, diagnosing, and treating heart, lung, blood, and sleep disorders.[nhlbi.nih.gov]
  • Benfotiamine prevents macro- and microvascular endothelial dysfunction and oxidative stress following a meal rich in advanced glycation end products in individuals with type 2 diabetes. Diabetes Care. 2006; 29(9):2064 – 71.[life-enhancement.com]



  1. Choudhury M, Boyett MR, Morris GM. Biology of the Sinus Node and its Disease. Arrhythmia & Electrophysiology Review. 2015;4(1):28-34.
  2. Romandini A, Scappini L. Sinoatrial Exit Block. Clinical Cases in Cardiology. Springer International Publishing; 2015:255-264.
  3. Kramarz E, Makowski K. Clinical significance of second degree Wenckebach type sinoatrial block identified during Holter monitoring in patients with symptoms suggestive of arrhythmia. Europace. 2015;17(1):123-130.
  4. Vogler J1, Breithardt G, Eckardt L. Bradyarrhythmias and conduction blocks. Rev Esp Cardiol (Engl Ed). 2012;65(7):656-667.
  5. Porter RS, Kaplan JL. Merck Manual of Diagnosis and Therapy. 19th Edition. Merck Sharp & Dohme Corp. Whitehouse Station, N.J; 2011.
  6. Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson J, Loscalzo J. eds. Harrison's Principles of Internal Medicine, 18e. New York, NY: McGraw-Hill; 2012.

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Last updated: 2018-06-22 08:07