Tachycardia-Bradycardia Syndrome

Tachycardia-bradycardia syndrome is one form of sick sinus syndrome, a disorder of the sinus node, the heart's natural pacemaker in the right atrium. In this syndrome, the heart rate alternates between too slow (bradycardia) and too fast (tachycardia). The fast phase is usually atrial fibrillation, and sometimes atrial flutter or atrial tachycardia.

Long Pauses After Episodes of Palpitations

The characteristic feature of this syndrome appears when an episode of fast heartbeat stops. The weak sinus node is slow to start working again, so the heart stops beating for a moment, sometimes for several seconds. During this pause, blood flow to the brain decreases, so you may feel very dizzy, have your vision go dark, or faint. Outside these episodes, the heart rate is often too slow and does not rise enough during activity, so you tire quickly.

The symptoms of this syndrome come and go, so an ECG recorded once often looks normal. Many people are only diagnosed after fainting, falling, or having their heart rhythm recorded over several days. Once treatment is underway, many people with this syndrome can return to their daily activities.

Why It Happens

The main cause is age-related change in the tissue of the sinus node and the atria, in which connective tissue replaces the pacemaker cells. That is why this syndrome is more common in older adults. Long-standing atrial fibrillation can also weaken the sinus node, and the reverse is also true. Heart disease, previous heart surgery, an underactive thyroid, electrolyte disturbances, and sleep apnea can also play a role. Medicines that slow the heart rate can make the pauses longer.

Finding the Right Balance in Treatment

Medicines that slow the heart rate during fast episodes can make the slow heart rate and the pauses worse. That is why many patients need a pacemaker, a device that keeps the heart rate from becoming too slow, so that medicines to control the fast heart rate can be used safely. In some patients, atrial fibrillation ablation can reduce the pauses so that a pacemaker can be avoided. The accompanying atrial fibrillation also increases the risk of stroke, so the doctor assesses whether you need medicine to prevent blood clots.

The slow heart rate is covered on the Bradycardia page, while the fast phase is covered on the Atrial Fibrillation page.

The doctor asks about your symptoms, especially dizziness or fainting that appears after palpitations, as well as all the medicines you take. An ECG can show a slow heart rate, sinus pauses, or atrial fibrillation, but it is often normal if taken outside an episode. That is why a Holter recording over 24 to 48 hours or a long-term recorder is used to capture the alternation between fast and slow heart rates, including the pause after an episode stops. If symptoms are infrequent, a small recorder implanted under the skin can record the rhythm for up to several years.

Echocardiography assesses the size of the atria, the valves, and the heart's pumping strength. Blood tests check the thyroid and electrolytes. A treadmill test can show whether the heart rate rises enough during activity. The doctor also assesses whether symptoms improve when certain medicines are adjusted, and calculates the stroke risk if atrial fibrillation is present.

Make an appointment with a doctor if you often feel dizzy, nearly faint, or tire quickly, especially if the symptoms appear after palpitations or when your heartbeat feels slow. Bring a record of your symptoms and a list of your medicines. Go to the emergency room right away if danger signs appear.

• Severe dizziness or vision going dark after an episode of palpitations stops
• A resting pulse that is often below 50 beats per minute, with weakness
• Fast palpitations that alternate with a slow heartbeat
• Dizziness after starting or increasing a heart medicine
• Fainting, chest pain, severe shortness of breath, or signs of stroke: go to the emergency room right away