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Sinus arrest is a condition in which the heart’s sinoatrial (SA) node, the heart’s primary pacemaker, has problems with the formation and propagation of electrical impulses. This results in a failure of the heart to beat. The condition is referred to as sinus pause if only one or two beats are missed and sinus arrest if more than two beats are missed. Sinus arrest is a form of sinus node dysfunction (SND).
In a healthy heart, the cardiac cycle is produced by a cyclical flow of electricity through the heart. The sinoatrial node fires an impulse through the atria, causing their muscles to contract and pump blood into the ventricles. The impulse then reaches the atrioventricular (AV) node. After a pause to allow the ventricles to fill with blood, the atrioventricular node retransmits the impulse to the ventricles. The contracting ventricles then pump blood out of the heart and to the rest of the body.
In the case of sinus arrest, there is a breakdown in the cardiac cycle, and the heart skips beats. This will continue until either the sinoatrial node impulse is effectively re-established or the atrioventricular node assumes the role of the pacemaker. These missed beats can be clearly identified on an electrocardiogram (EKG) strip.
The causes of this breakdown are typically related to either the formation or propagation of the electrical impulses. There might be a problem with the sinoatrial node, where formation of the impulse is the issue. There might also be problems with the heart’s conduction system, where the impulse is not being propagated properly. Conductive problems can stem from natural deterioration, hypothyroidism or electrolyte imbalances.
The effects of sinus arrest typically present themselves as cerebral or cardiac symptoms. Cerebral symptoms include dizziness, slurred speech, blank-outs and syncope. The most severe of these symptoms is syncope, or loss of consciousness, caused by lack of blood flow to the brain. Cardiac symptoms include palpitations, angina, congestive heart failure symptoms and, in severe cases, cardiac arrest. Mild incidents such as sinus pauses are often asymptomatic and can be detected only via an EKG.
Sinus arrest usually occurs in elderly patients, resulting from the natural deterioration of the SA node, atrial muscle and conductive system. This stage of sinus arrest is progressive in nature and irreversible. When sinus arrest occurs earlier in life, it normally is a complication of another cardiac problem or severe electrolyte imbalance.
Typically, no treatment is required for asymptomatic patients. For chronic sinus arrest, treatment involves the use of an artificial pacemaker. Research has shown that sinus node dysfunction occurs in about one out of every 600 cardiac patients who are more than 65 years old. Nearly half of these patients will develop tachy-brady syndrome at some point and will face a higher risk of stroke and death.
Survivability appears to depend on the overall health of the patient’s heart. A pacemaker will effectively treat sinus arrest, but it will not significantly change other underlying cardiac problems. In most cases, it is not sinus arrest that directly leads to death; rather, it is a combination of other chronic heart problems.