Sinus arrest is a medical condition affecting the heart’s electrical system, characterized by temporary pauses in the heart’s natural rhythm. It occurs when the heart’s primary pacemaker, the sinoatrial node, unexpectedly ceases to generate the electrical impulses that regulate heartbeats. These pauses impact cardiac function.
What Sinus Arrest Means
Sinus arrest refers to a transient cessation of electrical activity from the sinoatrial (SA) node, the heart’s natural pacemaker. Located in the right atrium, the SA node generates electrical impulses at a regular rate, coordinating the heart’s contractions. This interruption means there is no electrical activity for a period, appearing as an absence of P-waves and QRS complexes on an electrocardiogram (ECG).
This condition is a type of arrhythmia, an irregularity in the heart’s heartbeat. The duration of these pauses can vary, lasting from 2 seconds to several minutes. During a sinus arrest, auxiliary pacemakers in other parts of the heart, such as the atrioventricular junction or the ventricles, may take over to restore a rhythm, known as an “escape rhythm,” though often at a slower rate.
Common Causes
Degeneration and fibrosis of the sinoatrial nodal tissue, often age-related, are common intrinsic causes of sinus arrest. Certain medications can also suppress the SA node’s function, including beta-blockers, calcium channel blockers, and digoxin, commonly prescribed for blood pressure or heart rhythm management.
Electrolyte imbalances, such as high or low potassium (hyperkalemia or hypokalemia) and low calcium (hypocalcemia), can affect the SA node’s electrical stability. Increased vagal nerve stimulation can slow the heart rate and contribute to sinus arrest. Other conditions like hypothyroidism, myocardial ischemia, and certain cardiomyopathies can also cause it. Sinus arrest is also a feature of sick sinus syndrome, a group of heart rhythm problems stemming from a malfunctioning sinus node.
Signs and Symptoms
The symptoms of sinus arrest arise from the heart’s inability to pump enough blood efficiently to the body’s organs, particularly the brain, during the pauses. Some individuals may experience no symptoms, especially if the pauses are brief or infrequent. When symptoms do occur, they can include dizziness or lightheadedness due to reduced blood flow to the brain.
Fainting, also known as syncope, is a more severe symptom that can occur with longer pauses. Individuals might also report fatigue or shortness of breath, reflecting the body’s reduced oxygen supply. Palpitations, or the sensation of a pounding, racing, or skipped heartbeat, may also be noticed, particularly when the heart resumes its rhythm after a pause or when escape beats occur.
How Sinus Arrest Is Diagnosed
Diagnosing sinus arrest primarily relies on evaluating the heart’s electrical activity. An electrocardiogram (ECG or EKG) is a fundamental diagnostic tool that records the heart’s electrical signals and can reveal the characteristic pauses of sinus arrest. On an ECG, sinus arrest appears as a sudden absence of electrical activity, meaning no P-waves or QRS complexes are visible for a duration of at least 2 seconds.
For intermittent or infrequent pauses, longer-term monitoring may be necessary. A Holter monitor is a portable ECG device worn for 24 to 48 hours that continuously records heart activity during daily routines. Event recorders are similar devices that can be worn for longer periods, up to 30 days, and are activated by the patient when symptoms occur. These monitors help capture transient events that might be missed during a short-term ECG.
Treatment Approaches
Treatment for sinus arrest depends on the frequency and duration of the pauses, as well as the presence and severity of symptoms. For individuals who are asymptomatic and have infrequent, short pauses, close monitoring without immediate intervention may be sufficient. If medications are identified as a contributing factor, adjusting dosages or discontinuing the offending drugs can resolve the issue.
For symptomatic cases or those with prolonged pauses, especially those lasting 3 seconds or more, the implantation of a permanent pacemaker is the primary treatment. A pacemaker is a small device surgically placed under the skin near the collarbone, with wires extending to the heart. It works by delivering electrical impulses to the heart muscle when the SA node fails to fire, ensuring a consistent heart rate and preventing symptomatic pauses. This device helps maintain a steady heart rhythm and alleviates symptoms.