Sinoatrial arrest: Difference between revisions
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There is an unexpected drop of the P wave. Following this drop, there is a pause in the sinus cycle which is a multiple of the basic sinus cycle. Blocked atrial premature beats sometimes mimic second-degree sinoatrial block. Third-degree sinoatrial exit block cannot be distinguished from sinus arrest when the sinus node ceases to fire. Under such circumstances, subsidiary pacemakers in the AV junction or ventricles may take over. | There is an unexpected drop of the P wave. Following this drop, there is a pause in the sinus cycle which is a multiple of the basic sinus cycle. Blocked atrial premature beats sometimes mimic second-degree sinoatrial block. Third-degree sinoatrial exit block cannot be distinguished from sinus arrest when the sinus node ceases to fire. Under such circumstances, subsidiary pacemakers in the AV junction or ventricles may take over. | ||
==Symptoms== | |||
If the AV junctional or ectopic ventricular pacemaker is not sufficiently rapid to generate an adequate cardiac output, then end organ hypoperfusion may result with some of the following symptoms: | |||
*[[Angina]] | |||
*[[Congestive heart failure]] | |||
*[[Syncope]] | |||
==Differential diagnosis of underlying causes of sinus arrest== | ==Differential diagnosis of underlying causes of sinus arrest== | ||
*[[Digitalis]] including digitalis toxicity | *[[Digitalis]] including digitalis toxicity | ||
| Line 52: | Line 59: | ||
*[[Vagal reaction|Vagal tone]] | *[[Vagal reaction|Vagal tone]] | ||
== | ==Diagnosis== | ||
===Laboratory studies=== | |||
Serum K+, Ca+ and Na+ should be checked as should [[thyroid function tests]] to rule out [[hypothyroidism]]. | |||
==Treatment== | ==Treatment== | ||
Revision as of 18:53, 11 January 2010
| Sinoatrial arrest | |
| ICD-10 | I45.5 |
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| ICD-9 | 426.6 |
| MeSH | D012848 |
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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Overview
Under certain circumstances, the SA node fails to initiate an impulse at the expected time in the cardiac cycle. In the absence of an impulse from the SA Node neither the atria or the ventricles are stimulated and thus an entire PQRST complex drops out for 1 beat(or more). This is called Sinoatrial(SA) Arrest. In other instances the impulse is initiated normally but is blocked within the SA Node and never reaches the atria and ventricles. Sinus arrest is one variant of sinus node dysfunction.
Epidemiology
Sinus arrest is fairly uncommon. It is more likely to be observed in elderly patients with a senescent rhythm system. It can be observed in the setting of myocardial disease (myocarditis) and ischemia or infarction (particularly acute inferior or posterior ST segment elevation MI). It can be a manifestation of digitalis or lidocaine toxicity.
Pathophysiology
If there is absence of a p wave or a dropped p wave, it is difficult to determine from the surface EKG if this is 1) a loss of sinus node automaticity or 2) if this is a block of sinus node conduction. However, in patients with complete SA block, the block is frequently associated with atrial or AV junctional escape rhythms, while sinus arrest or pause is usually associated with depression of other potential atrial pacemakers, so that atrial escape is infrequent.
Sinoatrial block
In this disorder, p waves are being generated at a regular rate in a regular pattern which are a multiple of the basic sinus cycle.
Type I (Wenckebach phenomenon) sinoatrial exit block
The PP cycle is progressively shortened until there is a pause and the cycle is repeated. The pause is due to the dropped P wave and measures less than twice the PP cycle. It is similar to the behavior of the RR intervals in type I second-degree AV block.
Type II second-degree sinoatrial exit block
There is an unexpected drop of the P wave. Following this drop, there is a pause in the sinus cycle which is a multiple of the basic sinus cycle. Blocked atrial premature beats sometimes mimic second-degree sinoatrial block. Third-degree sinoatrial exit block cannot be distinguished from sinus arrest when the sinus node ceases to fire. Under such circumstances, subsidiary pacemakers in the AV junction or ventricles may take over.
Symptoms
If the AV junctional or ectopic ventricular pacemaker is not sufficiently rapid to generate an adequate cardiac output, then end organ hypoperfusion may result with some of the following symptoms:
Differential diagnosis of underlying causes of sinus arrest
- Digitalis including digitalis toxicity
- Hyperkalemia
- Decreased P wave amplitude occurs when the K is > 7.0 meq/li
- P waves may be absent when the K is > 8.8 meq/li
- The impulses are still being generated in the SA node and are conducted to the ventricles through specialized atrial fibers without depolarizing the atrial muscle
- Moderate or sever hyperkalemia can cause sinus arrest [1]
- Lidocaine
- Myocarditis
- Percutaneous coronary intervention of the proximal right coronary artery can obstruct the origin of the SA nodal artery in about 17% of patients (14 of 80 in one series). [2] Sinus arrest with junctional escape rhythm went on to develop in 4 of the 14 patients and one patient required a temporary ventricular pacing. There was resolution of the the junctional escape rhythm in all patients within 3 days of the sinus node artery occlusion.
- ST elevation myocardial infarction particularly inferior myocardial infarctions and posterior infarctions.
- Vagal tone
Diagnosis
Laboratory studies
Serum K+, Ca+ and Na+ should be checked as should thyroid function tests to rule out hypothyroidism.
Treatment
Acute
- Discontinue the agent that may be causing sinus arrest and treat hyperkalemia.
- Isoproterenol can be used to increase the rate of the escape pacemaker.
- Atropine can be given if the block may be due to heightened vagal tone
- Finally, a temporary pacemaker wire can be placed if the patient is symptomatic with end organ hypoperfusion as a result of the AV nodal or ventricular escape rhythm.
Chronic
- If sinus arrest is part of a chronic condition of sinus node dysfunction such as the tachycardia-bradycardia syndrome and if the patient is symptomatic, then permanent pacemaker placement may be neccessary.
References
- ↑ Bonvini RF, Hendiri T, Anwar A (2006). "Sinus arrest and moderate hyperkalemia". Annales De Cardiologie Et D'angéiologie. 55 (3): 161–3. PMID 16792034. Unknown parameter
|month=ignored (help) - ↑ Munenori Kotoku, Akira Tamura, Shigeru Naono and Junichi Kadota.Sinus arrest caused by occlusion of the sinus node artery during percutaneous coronary intervention for lesions of the proximal right coronary artery. Heart and vessels,2007, p.389-392