Cardioinhibitory vasovagal syncope

30 May 26 | Dr Boon Lim & Mohamed Zuhair

Introduction

Fainting is common, affecting up to 40% of people at least once in a lifetime. However, for some people, however, fainting is not just an occasional inconvenience. It can happen repeatedly, without warning, and have a major impact on work, driving, education, exercise and quality of life.

One of the most important causes of recurrent fainting is a condition called cardioinhibitory vasovagal syncope. In this condition, the body’s normal reflexes become overactive and can suddenly slow the heart dramatically, sometimes causing the heart to pause altogether for several seconds.

The good news is that understanding why these episodes happen can help people take practical steps to reduce their risk. In selected patients, newer treatments such as Cardioneuroablation (CNA) may offer an alternative to a permanent pacemaker.

This article explains what cardioinhibitory syncope is, why it happens, and what treatment options may be available.

What is Cardioinhibitory Syncope?

The word “syncope” simply means a temporary loss of consciousness caused by reduced blood flow to the brain.

In cardioinhibitory syncope, the main problem is that the heart suddenly slows down too much.

The vagus nerve, a major nerve that helps regulate the heart, becomes excessively activated.

This can cause:

• A very slow heart rate (bradycardia)

• A pause in the heartbeat (asystole)

• Temporary interruption of blood flow to the brain

When this happens, a person may feel:

• Light-headed

• Sweaty

• Nauseated

• Warm

• Dizzy

before eventually collapsing or fainting.

In some people the heart may stop for several seconds before restarting spontaneously.

Although these pauses can be frightening, they are usually caused by an exaggerated reflex rather than a dangerous heart rhythm disorder, or structural heart disease.

Dysautonomia:

Dysautonomia refers to dysfunction of the autonomic nervous system, which is responsible for regulating involuntary bodily functions such as heart rate, blood pressure, digestion, and body temperature. In dysautonomia, the autonomic nervous system does not function properly, leading to a wide range of symptoms affecting various body systems.

Why does it occur?

The body is designed to protect us from danger. Unfortunately, in some people, the nervous system overreacts to certain triggers.

The vagus nerve suddenly becomes overactive and sends powerful signals to the heart. This can slow the heart dramatically and lower blood pressure at the same time. The result is reduced blood flow to the brain and loss of consciousness.

Common triggers include:

• Blood tests

• Cannulas

• Needles

• Seeing blood

Some people have more unusual triggers.

These include:

• Swallowing food or drink (swallow syncope)

• Severe abdominal pain

• Gastrointestinal cramping

In all of these situations, the underlying problem is usually an exaggerated vagal reflex. In particular the gastrointestinal tract has a rich innervation of nerves (which is why it is referred to as the second brain), second in nerve denstiy to the brain, and therefore when there is activation of the nervous system through “sensory input” , including pain, cramping, fullness in rectum – i.e. feeling the need to defecate, this can trigger a very strong vagal reflex, which may lead to cardioinhibitory syncope.

Management

Patients often underestimate how effective simple measures can be.

Hydration

Aim for 2–3 litres daily (if medically appropriate)
Start hydration early in the day

Salt Intake

Increased salt intake may help maintain blood volume
Discuss with your doctor first

Recognise Early Warning Signs and Take Early Evasive Action

Typical warning symptoms:

Sweating
Nausea
Tunnel vision
Feeling warm
Dizziness

Counterpressure Manoeuvres

When symptoms begin:

Leg crossing
Buttock clenching
Hand gripping
Squatting

These techniques can increase blood pressure and delay or prevent fainting.

Avoid Triggers Where Possible

Examples:

Sit down for blood tests
Lie flat during injections
Avoid dehydration
Avoid prolonged standing

How is a Diagnosis of Cardioinhibitory Vasovagal Syncope Made?

Diagnosing cardioinhibitory vasovagal syncope often involves putting together several pieces of a puzzle. The first and most important step is listening carefully to the patient’s story. Doctors will usually ask:

• What happened before the faint?

• Were there any warning symptoms?

• Was there a trigger?

• How long did the episode last?

• How quickly was recovery afterwards?

Many people with cardioinhibitory vasovagal syncope describe feeling warm, sweaty, nauseated, light-headed or dizzy before losing consciousness. The eventual loss of conscioussness may be more dramatic than a typical vasovagal syncope “faint” which may be more to do with a low blood pressure. Occsionally, with prolonged heart pauses, reflex anoxic movements (which mimic seizures) may occur. During these occasions, instead of slumping to the floor limp and unmoving, the patient may appear tense, rigid, with eyes open, and wiht hyperextension of arms and legs, as if stretching out “long” with rhythmic jerking which typically recovers quickly after the heart resumes conduction.

Common triggers include blood tests, injections, pain, emotional distress, prolonged standing or hot environments.

However, it is not possible from symptoms alone, to prove that the heart slowed excessively during the event.

For that reason, other tests are normally performed to try to capture the heart rhythm contemporaneously during the next syncopal event.

Ambulatory ECG Heart Rhythm (Holter) Monitoring

Portable heart monitors can record the heart rhythm over days or weeks.

Examples include:

• Holter monitors • Event recorders • Wearable monitors

These tests may occasionally capture an episode if symptoms occur frequently (typically once a week)

Implantable Loop Recorder (ILR)

For patients with infrequent (less than once every fortnight) but significant faints, an Implantable Loop Recorder is often one of the most useful tests available. This small device is placed under the skin of the chest and continuously records the heart rhythm for several years.

If a patient experiences a blackout, the device can reveal exactly what happened to the heart during the episode.

In some patients, recordings show dramatic slowing of the heart or even complete pauses lasting several seconds. This provides strong evidence for cardioinhibitory vasovagal syncope.

Tilt Table Testing

Tilt table testingis one of the most commonly used investigations for suspected vasovagal syncope. During the test, the patient is strapped safely onto a special table which is tilted upright while heart rate and blood pressure are monitored.

The aim is to reproduce the body’s abnormal reflex under controlled conditions.

In patients with cardioinhibitory syncope, tilt testing may demonstrate:

• Sudden slowing of the heart • Prolonged pauses in the heartbeat • A fall in blood pressure • Reproduction of the patient’s usual symptoms

The test can help identify whether fainting is primarily caused by slowing of the heart (cardioinhibition), a fall in blood pressure (vasodepression), or a combination of both.

Is One Test Enough?

Often, no single test provides the complete answer.

Doctors combine information from:

• The patient’s history • Witness accounts • ECG findings • Heart rhythm monitoring • Tilt table testing • Implantable loop recorder recordings

The most convincing diagnosis is made when a patient’s typical symptoms occur at the same time as documented slowing or stopping of the heart.

Occasionally your expert syncope doctor may suspect that you have both typical vasovagal syncope, but on occasion, significant cardioinhibitory syncope, where your symptoms may be particularly severe, or occurring with specific triggers such as abdominal pain or cramp. In these instances, even if a tilt was positive for vasovagal syncope with low blood pressures (but without cardioinhibition), your doctor may choose to offer you an implantable loop recorder.

Why Is an Accurate Diagnosis Important?

Understanding exactly why a person faints helps guide treatment.

Patients whose episodes are caused predominantly by excessive slowing of the heart may be candidates for treatments such as Cardioneuroablation (CNA) or, in selected circumstances, a pacemaker.

The more accurately the mechanism is identified, the more likely it is that treatment can be tailored successfully to the individual patient.

What if conservative treatment fails, and patients continue to get cardioinhibitory vasovagal syncope symptoms?

How Is Cardioinhibitory Vasovagal Syncope Treated?

Treatment is usually approached step by step.

Most people do not need invasive procedures and can achieve significant improvement through education, trigger avoidance, increased fluid intake, increased salt intake (where appropriate), and physical counter-pressure manoeuvres.

For patients who continue to experience recurrent fainting despite these measures, medications such as midodrine or fludrocortisone may be considered. These treatments can be helpful for some people, although they do not work for everyone.

The most important next step is establishing exactly what is happening during an episode. If testing shows that the heart is slowing dramatically or stopping for several seconds during a faint, this is known as cardioinhibitory vasovagal syncope.

For patients with severe, recurrent symptoms that continue despite conservative treatment, two advanced treatment options may be considered:

• Cardioneuroablation (CNA)

• Permanent pacemaker implantation

The choice between these treatments depends on several factors, including age, the pattern of fainting, the results of testing, and patient preference.

Patients Under 40 Years of Age

In younger patients, Cardioneuroablation is often an attractive option because it aims to treat the abnormal reflex itself rather than simply protecting against the slow heart rate.

Many younger patients prefer to avoid a lifelong implanted device if possible. Current evidence suggests that carefully selected younger patients with documented cardioinhibitory syncope may achieve excellent results with CNA.

For this reason, many specialists would consider CNA before pacemaker implantation in patients under 40 years old.

Patients Over 60 Years of Age

In older patients, permanent pacemakers currently have the strongest evidence base and are supported by international guidelines.

Pacemakers do not prevent the reflex from occurring, but they can prevent the profound slowing or stopping of the heart that contributes to loss of consciousness.

For patients over 60 years old with documented cardioinhibitory syncope, a pacemaker is often considered the first invasive treatment option.

Patients Between 40 and 60 Years of Age

For patients in this age group, there is rarely a single “correct” answer.

Both CNA and pacemaker therapy may be reasonable options.

The decision usually depends upon:

• The frequency and severity of symptoms

• The degree of heart slowing or pauses

• The results of tilt-table testing and heart rhythm monitoring

• Other medical conditions

• Whether the patient wishes to avoid a permanent implanted device

• The experience and availability of local specialist centres

In many cases, a detailed discussion between patient and specialist is required to determine which option best fits the individual’s circumstances and goals.

A Possible Treatment Pathway

Step 1:
Education, hydration, salt, trigger avoidance and physical counter-pressure manoeuvres.

Step 2:
Consider medications such as midodrine or fludrocortisone if symptoms persist.

Step 3:
Confirm the diagnosis using heart rhythm monitoring, implantable loop recorder recordings and/or tilt-table testing.

Step 4:
If severe cardioinhibitory syncope continues despite treatment:

• Under 40 years: consider Cardioneuroablation first.

• Between 40 and 60 years: individualised discussion regarding CNA versus pacemaker.

• Over 60 years: pacemaker therapy is often considered first-line.

Step 5:
Ongoing follow-up with a syncope or heart rhythm specialist.

The most important message is that treatment should always be individualised. Age is an important guide, but the final decision should be based on the patient’s symptoms, test results, lifestyle and personal preferences, and availability of treatment options.

Pacemakers - what are they and do I need to have one implated ?

A pacemaker is a small electronic device that is implanted under the skin, usually just below the collarbone, to help control the heart rate. It monitors the heart’s natural electrical activity and, if the heart beats too slowly or pauses for too long, the pacemaker delivers tiny electrical impulses to stimulate a heartbeat.

Pacemakers are commonly used to treat conditions that cause an abnormally slow heart rate (bradycardia), including some patients with severe cardioinhibitory vasovagal syncope where prolonged pauses in the heartbeat can lead to blackouts. Modern pacemakers only work when needed, remaining inactive when the heart is beating normally.

The device is connected to the heart by one or more thin wires (called leads) and is implanted during a minor procedure, usually under local anaesthetic. Most people return to normal activities within a few weeks and can live full, active lives with a pacemaker.

A pacemaker is usually recommended for patients who are older than 60yo who have recurrent cardioinhibitory syncope. In patients under 40, a pacemaker is often not the preferred first option because it treats the slow heart rate but not the underlying reflex causing the faints, and may require lifelong device follow-up and future replacement procedures. Some patients may learn to manage the condition with conservative strategies, whilst others may be considered for an emerging novel treatment, Cardioneuroablation (CNA)

CardioNeuro Ablation (CNA) for cardioinhibitory vasovagal syncope

Cardioneuroablation (CNA) is a minimally invasive catheter procedure that aims to reduce the excessive vagal nerve signals that can cause the heart to slow down or stop during a vasovagal faint. Using thin tubes (catheters) inserted through veins in the leg, the doctor identifies and treats small collections of nerve tissue on the surface of the heart called ganglionated plexi. By reducing these overactive nerve signals, CNA may help prevent the profound slowing of the heart that leads to blackouts.

Unlike a pacemaker, which treats the slow heart rate once it occurs, cardioneuroablation aims to modify the underlying reflex responsible for the faint. It is an emerging treatment that may be particularly attractive for younger patients with severe cardioinhibitory vasovagal syncope who wish to avoid lifelong pacemaker therapy. This is a novel procedure which is not widely accessible, but emerging promising studies suggest that this may be an effective strategy at preventing further episodes of cardioinhibitory syncope in younger patients.

To find out more about cardioneuroablation, click on this link – What is cardioneuroablation?