Sick sinus syndrome (SSS) is a heart rhythm disorder caused by a malfunction of the heart’s natural pacemaker, the sinus node. Located in the upper right chamber, the sinus node generates electrical signals that regulate heart rhythm. When it doesn’t function correctly, the heart’s ability to maintain a consistent beat is disrupted.
Understanding Sick Sinus Syndrome
In sick sinus syndrome, the sinus node malfunctions, leading to various abnormal heart rhythms. This can manifest as a heart rate that is too slow (persistent sinus bradycardia, typically fewer than 60 beats per minute), too fast, or an alternation between slow and fast rhythms (bradycardia-tachycardia syndrome). Another form is sinus arrest, which involves temporary pauses in the heart’s electrical activity. These malfunctions often stem from age-related degeneration of the sinus node tissue, though certain medications or underlying heart conditions can also contribute.
Common Symptoms of Sick Sinus Syndrome
Individuals with sick sinus syndrome may experience a range of symptoms, which often arise when the heart’s irregular rhythm prevents it from pumping enough blood to the body. Fatigue is common, as the body’s tissues may not receive sufficient oxygen and nutrients. Dizziness and lightheadedness can occur due to reduced blood flow to the brain, potentially leading to fainting spells (syncope).
Shortness of breath, particularly with physical activity, can indicate the heart is struggling to meet oxygen demands. Some people also report chest pain or discomfort, alongside palpitations, which are sensations of the heart racing, pounding, or skipping beats. These symptoms often fluctuate in severity and may be intermittent, making them challenging to identify without careful observation.
Diagnostic Tools and Tests
Diagnosing sick sinus syndrome involves a variety of medical tests designed to capture and analyze the heart’s electrical activity over time. The electrocardiogram (ECG or EKG) is often the initial test, recording the heart’s electrical signals at rest. However, a standard ECG may not always detect SSS if the irregular rhythms are intermittent and not present during the brief recording period.
To address this, portable monitoring devices are frequently employed. A Holter monitor, worn for 24 to 48 hours, continuously records the heart’s electrical activity during daily routines, increasing the chance of capturing irregular rhythms. For symptoms that occur less frequently, an event monitor or a loop recorder may be used for longer periods, sometimes weeks or months, allowing patients to activate the recording when symptoms occur.
In some cases, an electrophysiology (EP) study provides a more detailed assessment of the heart’s electrical system. This invasive procedure involves threading catheters into the heart to measure electrical signals directly. Specific measurements, such as sinus node recovery time (SNRT) and sinoatrial conduction time (SACT), can indicate sinus node dysfunction. A tilt table test may also be performed, particularly if fainting is a primary symptom, to observe how heart rate and blood pressure respond to changes in body position.
Interpreting Diagnostic Findings
The information collected from these diagnostic tests is carefully analyzed to determine if sick sinus syndrome is present. When evaluating ECG or ambulatory monitor findings, medical professionals look for persistent slow heart rates (bradycardia), pauses in the heart’s rhythm (sinus arrest or sinus pauses), or alternating fast and slow rhythms (bradycardia-tachycardia syndrome).
During an electrophysiology study, prolonged sinus node recovery time (SNRT) and abnormal sinoatrial conduction time (SACT) provide objective evidence of impaired sinus node function. If a tilt table test is conducted, an abnormal drop in heart rate or blood pressure that correlates with the patient’s reported symptoms, especially fainting, further supports a diagnosis of sick sinus syndrome.