Slow Rhythm and Conduction Disorder
Bradycardia & Conduction Disorders
Bradycardia means a slower heart rate than expected. It is often harmless, but it can also be caused by a problem with the heart’s electrical system, including conduction disorders.
On this page
Understanding the rhythm
What Is Bradycardia?
Bradycardia is a heart rhythm that is slower than expected for the person and the situation. A slow heart rate is not always a problem. It matters mainly when it causes symptoms or reflects a problem with the heart’s electrical system.
Slow rhythms can come from the heart’s natural pacemaker, the sinus node, or from delays and blocks in the pathway that carries the impulse to the ventricles.
Heart electrical system, conceptual illustration
How the heart sets its pace
Normal Heart-Rate Control
The sinus node, in the upper right chamber, normally starts each beat. The impulse then passes through the atria to the AV node, which lets it continue to the ventricles after a short delay.
The nervous system and hormones adjust the rate to the body’s needs. The rate is lower at rest and during sleep and higher with activity, so there is no single normal figure for everyone.
Sinus node and AV node, conceptual illustration
Clinical contexts
Causes and Clinical Contexts
A slow rate can be a normal finding or a sign of an underlying problem. The cause is considered together with symptoms and tests.
Normal variation
Fit people and people at rest or asleep can have lower heart rates without any problem.
Ageing of the conduction system
The electrical system can change with age.
Medicines
Some medicines can slow the heart rate or conduction.
Other conditions
Heart disease, thyroid or electrolyte problems and other illnesses can play a part.
Some people alternate between slow and fast rhythms, including atrial fibrillation.
A problem of rate
Sinus Node Dysfunction
In sinus node dysfunction, the natural pacemaker fires too slowly, pauses, or does not increase the rate as expected with activity. It is sometimes called sick sinus syndrome.
Some people have symptoms only at times. Longer monitoring may be needed to catch an episode.
A problem of conduction
AV Conduction Problems
In atrioventricular (AV) block, the impulse is delayed or fails to pass from the atria to the ventricles. Blocks are described by degree, and the degree helps guide the assessment.
Delayed
All impulses pass, but more slowly than usual.
Intermittent
Some impulses do not pass, so beats are dropped.
Complete
No impulses pass to the ventricles, which then rely on a slower backup rhythm.
Assessment
The type of block and the symptoms guide what is done next.
The significance of AV block depends on the type, the level of the block and the person’s symptoms.
What people notice
Symptoms
Many people with a slow heart rate have no symptoms. When symptoms occur they can include the following.
Tiredness
Feeling unusually tired or weak.
Light-headedness
Feeling dizzy or unsteady.
Fainting
Blacking out or near-fainting.
Breathlessness
Feeling short of breath, especially with activity.
Reduced exercise tolerance
Being unable to do activities that were easy before.
Fainting or chest pain needs urgent medical care.
What the ECG may show
ECG
An ECG can show the rate and the relationship between the atrial and ventricular signals. It can show a slow sinus rhythm, pauses, or different patterns of AV block.
An ECG records only a short period. If slow rhythms come and go, it may be normal at the time of the test. The ECG is interpreted by a physician together with the symptoms.
Catching the rhythm
Rhythm Monitoring
Monitoring links symptoms to the actual rhythm. The choice depends on how often symptoms occur.
Continuous recording over a period of time. Useful when symptoms occur often.
Used for less frequent symptoms and can record over a longer time.
Symptom diary
Writing down when symptoms happen helps match them to the recording.
Finding the cause
Diagnostic Evaluation
The evaluation looks for the reason for the slow rhythm and for any link to symptoms.
History
Symptoms, activity, medicines and family history.
Examination
Pulse, blood pressure and heart examination.
ECG
A recording of the rhythm at rest.
Blood tests
To look for related conditions.
Monitoring
Recording over time when symptoms are intermittent.
Further tests
Exercise testing, heart imaging or an electrophysiology study, where needed.
Planning care
Treatment Approach
Treatment depends on the cause and on whether the slow rhythm explains the symptoms. Many people need no treatment.
Observation
If there are no symptoms and the rhythm is not a concern, follow-up may be enough.
Review of medicines
Medicines that slow the heart may be changed if appropriate.
Treating the cause
Other conditions that contribute are treated.
Considered in selected patients, as described below.
Device treatment
When Pacing May Be Considered
A pacemaker may be considered when a slow rhythm is the likely cause of symptoms and is not reversible, or when the type of conduction block carries a risk of dangerous pauses. The decision is individual and made by the treating physician.
A pacemaker sends small electrical impulses to the heart when its own rhythm is too slow. For details about the device and implantation, see the Pacemaker page.
Pacemaker placement, conceptual illustration
Pacing decisions
How Pacing Decisions Are Approached
Symptomatic bradycardia
When a slow rhythm is documented at the time of symptoms such as fainting, near-fainting or marked tiredness, and no reversible cause is found, pacing may be considered.
Reversible causes first
Medicines, electrolyte or thyroid problems and other conditions are reviewed first, because correcting them can sometimes resolve the slow rhythm.
Sinus node dysfunction
Pacing is considered mainly when symptoms are linked to the slow rhythm, to pauses, or to a rate that does not rise enough with activity.
AV block
The type and level of block matter. Some forms carry a risk of dangerous pauses and may be treated with pacing even without symptoms, while milder forms may need only follow-up.
Reflex-related slow rhythms
In vasovagal syncope with documented pauses, pacing or other measures may be discussed. See Vasovagal Syncope and Cardioneuroablation.
How the pacemaker assessment fits
Before a device is advised, the team confirms the link between rhythm and symptoms, reviews medicines and heart imaging, and chooses a device type to suit the rhythm problem. See Pacemaker for implantation, device checks and living with a device.
Ongoing care
Follow-up
Follow-up depends on the cause and on whether treatment was needed. It can include symptom review, repeat monitoring and, for patients with a device, regular device checks.
Seek urgent medical care for fainting, chest pain or severe breathlessness.
Questions