Sinoatrial arrest
| Sinoatrial arrest |
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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.
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.
Differential diagnosis of underlying causes of sinus arrest
- 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
- 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.
Sinus arrest is an uncommon rhythm disturbance, but is occasionally noted in elderly patients, in those with ischemic heart disease (particularly with acute inferior or true posterior MI), in some patients with myocardial disease and sometimes with digitalis toxicity. The treatment of SA pause or arrest ordinarily includes administration of atropine or temporary or permanent ventricular pacing. Reasons to pace sinus pause or sinus arrest include the development of an AV junctional or ectopic ventricular pacemaker that is slow enough to result in such problems as syncope, CHF, angina, or frequent ventricular ectopic beats. If the escape AV junctional or ectopic ventricular pacemaker is rapid enough, particularly if the pacemaker is an AV junctional one, it may not be necessary to treat the underlying sinus pause or arrest except to ensure that it is not due to digitalis toxicity and, when possible, to determine its etiology. If this rhythm disturbance is associated with brady- or tachyarrhythmias and appears to be an integral part of the sick sinus syndrome, then pacemaker therapy is indicated. Pacemaker therapy is also indicated when any of the above-mentioned signs or symptoms are a consequence of the slower AV junctional ectopic pacemaker.
Treatment
- Discontinue the agent that may be causing sinus arrest and treat hyperkalemia.
- Isoproterenol can be used to increase the rate of the escape pacemaker.
- Finally, a temporary pacemaker wire can be placed.
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