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.

• Fever

  We report a ten-year-old girl who presented with dengue haemorrhagic fever with sinoatrial block and atrioventricular dissociation that had a spontaneous resolution. [ncbi.nlm.nih.gov]

  […] disease (calcification of the conduction system and valves), noncompaction cardiomyopathy, nail-patella syndrome, mitochondrial myopathy [6] Infectious causes: Lyme borreliosis (particularly in endemic areas), Trypanosoma cruzi infection, [7] rheumatic fever [emedicine.medscape.com]

• 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]

  A left bundle branch block usually is a sign of an underlying heart disease, including dilated cardiomyopathy, hypertrophic cardiomyopathy, high blood pressure, aortic valve disease, coronary artery disease and other heart 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]

  ICD-10-CM Codes › I00-I99 Diseases of the circulatory system › I30-I52 Other forms of heart disease › I49- Other cardiac arrhythmias › Other specified cardiac arrhythmias 2016 2017 2018 2019 Billable/Specific Code I49.8 is a billable/specific ICD-10-CM [icd10data.com]

• Chest Pain

  In some people, they can cause fainting, altered mental status, chest pain, hypoperfusion, and signs of shock. They can also lead to cessation of the SA node and more serious dysrhythmias. [en.wikipedia.org]

  […] heart block include: fainting – this can cause someone to collapse breathlessness extreme tiredness (fatigue), sometimes with confusion chest pain having a slow heart beat (bradycardia), or feeling a skipping, fluttering or pounding in your chest (palpitations [nhs.uk]

  Others will have symptoms that may include fainting (syncope), dizziness lightheadedness, chest pain, and shortness of breath. [life-enhancement.com]

• Vertigo

  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. [symptoma.com]

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].

• Narrow QRS Complex

  Pacemakers above the His bundle produce a narrow QRS complex escape rhythm, whereas those at or below the His bundle produce a wide QRS complex. [emedicine.medscape.com]

• 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]

• Third Degree Atrioventricular Block

  It is first degree when atrioventricular conduction time is prolonged; it is called second degree or partial when some but not all atrial impulses reach the ventricle; and it is called third degree or complete when no atrial impulses at all reach the [medical-dictionary.thefreedictionary.com]

  Although it may initially appear as a first- or second-degree atrioventricular block, most cases present with fetal bradycardia and complete third-degree atrioventricular block. [doi.org]

• 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]

  arrest Sinus arrest with junctional escape Sinus arrest with ventricular escape Clinical Information A blockage of electrical conduction within the sinoatrial node resulting in the failure of impulse transmission from the sinoatrial node A blockage of [icd9data.com]

  Sinus Block and Sinus Arrest NOTE: With SA Block the R-R interval measurement can be within plus or minus 2 small boxes. If it is greater than the plus or minus 2 small boxes it is a sinus arrest. [unm.edu]

  An outer layer of transitional cells ( T cells ) that transmit the sinus impulses out into the right atrium. Sinus node dysfunction can result from either: Failure of the P cells to produce an impulse. This leads to sinus pauses and sinus arrest. [lifeinthefastlane.com]

• Premature Atrial Contractions

  The premature atrial contractions traveled anterograde via the anomalous pathway and were blocked distally to the His bundle. [ncbi.nlm.nih.gov]

• Torsades De Pointes

  Adult male mice lacking Ca v 3.1 alpha subunits after induction of complete atrioventricular block showed slower escape rhythms, greater mortality and higher frequency of torsades de pointes than control mice. [doi.org]

The correlation between lithium treatment and tachyarrhythmias is discussed. [ncbi.nlm.nih.gov]

They are not as serious as an AV block and most often do not require treatment. In some people, they can cause fainting, altered mental status, chest pain, hypoperfusion, and signs of shock. [en.wikipedia.org]

KEYWORDS: Holter monitoring; Prognosis; Sinoatrial Wenckebach block [ncbi.nlm.nih.gov]

Overall, the prognosis is favorable. [emedicine.medscape.com]

Prognosis of sinus node dysfunction is mixed; without treatment, mortality is about 2%/year, primarily resulting from an underlying structural heart disorder. Each year, about 5% of patients develop AF with its risks of heart failure and stroke. [merckmanuals.com]

Etiology SA block is uncommon and usually occurs transiently May occur in healthy clients 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]

While the etiology of this disease has remained obscure for long time, there is now strong evidence that loss-of-function of Ca v 1.3 and Ca v 3.1 channels underlie this pathology ( Strandberg et al., 2013 ). [doi.org]

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

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]

Antiarrhythmic drugs may prevent paroxysmal tachyarrhythmias after pacemaker insertion. Theophylline and hydralazine are options to increase heart rate in healthy, younger patients who have bradycardia without syncope. [merckmanuals.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]

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]

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.