Sinoatrial arrest overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
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 nor 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. This is called sinus exit block or sinoatrial block. Sinus arrest is one of several variants of sinus node dysfunction. The word sinus pause is used to indicate a pause in the generation of QRS complexes for 3 seconds or less. If the delay is longer than this, then the term sinus arrest is used. If there is a markedly prolonged or permanent cessation of P wave and QRS complexes, then the term asystole is applied.
Pathophysiology
In sinoatrial arrest, the SA node is not generating electrical complexes due to impairment of automaticity. In patients with sinus arrest, the pause is more frequently associated with either an atrial or an AV junctional escape rhythm. If associated with sick sinus syndrome, lower pacemakers are impaired as well, therefore it can present as a complete absence of electrical activity on EKG.
Causes
Sinus arrest is fairly uncommon. 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.
Epidemiology and Demographics
Sinus arrest is fairly uncommon. It is more likely to be observed in elderly patients with a senescent rhythm system.
Diagnosis
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.
Laboratory Findings
Serum K+, Ca+ and Na+ should be checked as should thyroid function tests to rule out hypothyroidism.