Bradycardia

Diagnosis

Bradycardia might originate in three basic sites: the sinus node, conduction system, or autonomic nervous system.

Sick Sinus Syndrome describes the bradycardia that originates in the heart's sinus node, which is the "spark plug" that distributes the electrical signal throughout the heart muscle. If the sinus node does not spark properly, it can slow the heart rate, or slow it and then speed it up. Sick sinus syndrome is common in older people. It sometimes happens during episodic atrial fibrillation (when the heart beats too fast.)

Stokes-Adams Heart Block describes the bradycardia that originates in the conduction system. Defects in the conduction system can block electrical impulses from reaching the heart's lower chambers (ventricles), slowing the heart rate.

The third site, the autonomic nervous system, involves the nerves that control the speed of the heartbeat.

A comprehensive diagnosis at Mayo Clinic helps determine what is causing the bradycardia. In the diagnosis process, the patient may be asked about or tested for conditions that may trigger the slower heart rate, such as medications or heart disease.

Heart Monitoring Tests

The patient may have two heart monitoring tests: active and passive.

Active Tests

These tests try to induce an irregular heartbeat while the patient monitored closely. They include:

• Electrophysiology (EP) testing and mapping
  Mayo Clinic is an international leader in catheter ablation and implantable devices and uses the most advanced technology to treat arrhythmias. Mayo has over 25 years of experience in treating patients who have various heart arrhythmias.

  In the EP test, catheters (thin, flexible tubes) with electrodes at the tips, are threaded through the patient's blood vessels to various spots within the heart. Once in place, the electrodes can precisely map the spread of electrical impulses through the heart. During the test, the electrophysiologist (a cardiologist who specializes in heart rhythms) may use the electrodes to stimulate the heart to beat at rates that may trigger — or halt — an irregular heartbeat. The physician can observe the location of the arrhythmia and the mechanics of the heart that may be causing the irregular heartbeat.

  The ability to trigger and stop a bradycardia may also be used to test the effectiveness of various treatment methods. For example, if catheter radiofrequency ablation — a catheter-based treatment option for many arrhythmias — is determined by the doctor to be appropriate treatment, the procedure can be performed during EP testing. Read more about catheter radiofrequency ablation.

• Stress test
  Bradycardia may be triggered or worsen when the patient exercises. During a stress test, the patient may exercise on a treadmill or stationary bicycle, while an electrocardiogram (ECG) monitors heart activity. The test may involve a drug to stimulate the heart similar to stimulation during exercise. This may help patients who have difficulty exercising. The stress test can also be used to detect coronary artery disease.

Passive Tests

These tests involve monitoring the heart during regular activity. They include:

• Electrocardiogram (ECG)
  Electrodes (sensor patches with wires attached) are placed on the patient's skin to measure electrical impulses given off by the heart. The ECG measures the timing and duration of each electrical phase in the heartbeat.
• Holter monitor
  A Holter monitor is a portable ECG device that the patient wears for a day or more to record the heart's electrical activity during daily routine.
• Echocardiogram (Doppler echocardiogram)
  Sound waves produce detailed images of the patient's heart. Through a handheld device (transducer) on the patient's chest, sound waves bounce off the heart and are reflected to produce video images of the heart's size, structure and motion. The echocardiogram can also be used to measure the heart's blood volume and the speed and direction of blood flow through the heart.

Blood tests

These may help to identify whether medication, a thyroid problem or other medical problems are causing the bradycardia.

The comprehensive diagnosis is critical in determining the best treatment options.