ICD Shocks : What you need to know

One of the biggest fears of someone who’s had an SCA is that it will happen again one day.  For some, surgery and medications will be enough to reduce the chances of it happening, but for others an Implantable Cardioverter Defibrillator will be required.  Whilst many find reassurance in one of these devices they can also bring their own anxieties and fears regarding any potential treatment delivered, especially shocks.

What does ICD treatment feel like?

This varies greatly from one person to another. The information below is a rough guide to what it might feel like. If an ICD is delivering pacing impulses, you may feel some palpitations – like a “fluttering” in your chest. If you have an arrhythmia that triggers the ICD to deliver an electrical shock (either as defibrillation or cardioversion), it is possible that you may collapse or become unconscious before the treatment is delivered. If this happens, you may not feel anything when you get the electrical shock. However, if you are conscious when the shock is delivered, it may feel like a fairly heavy thump in your chest or back. You may find this distressing – especially the first time it happens. The shock is less intense than a shock from mains electricity or from a spark plug of a car. ICDs are programmed to meet a person’s needs, but typically, an ICD will be set to deliver 20-35 joules per shock. Which is much lower an than external defibrillator shock which typically ranges from 120-200 joules

Will I get any warning?

Some people don’t get any warning before the shock is delivered. Other people can get warning symptoms before the shock – for example, dizziness or palpitations.

If the rhythm disturbance is serious, it is possible that you may collapse before the shock is delivered. So, if you do get any warning symptoms, you should sit down or lie down so that you don’t hurt yourself. 

It’s also worth knowing that if your ICD makes a beeping sound it does not indicate that you are about to receive a shock. It’s a Patient Alert feature to let you know you need to have a doctor check your ICD

Appropriate Shocks

An appropriate shock is just that, appropriate. It means that your heart has gone into a dangerous arrhythmia and requires intervention to terminate it. This is where the ICD earns it’s worth and delivers a life saving shock.

Inappropriate Shocks

An inappropriate shock is one that your ICD has delivered but was not actually required.  This may be for a number of reasons including a malfunction or incorrect programming.  Some research shows that these account for 10-24% of all actual shocks, but are diminishing as ICD software and programming improve.  If you receive any type of shock you should ensure your ICD clinic has checked it such that you know whether it was appropriate or not i.e. if it saved your life.  If it was inappropriate you may need to visit your hospital for your ICD to be looked at.  Common causes of inappropriate shocks are Supra-ventricular Tachycardia (SVT), Non-Sustained Ventricular Tachycardia (NSVT), over-sensing and mechanical malfunctions.

Phantom Shocks

A phantom shock is just what it sounds like, the patient perceives an ICD shock, even though the device indicates that no therapy has been delivered. 

Patients with an ICD face psychological, physical, and social adjustments. Patients with an ICD, in general, have been shown to have high levels of anxiety, depression, and a sense of helplessness.

A subset experiences a phenomenon of phantom shock, which may represent a manifestation of anxiety, depression, or other emotional disturbance. It is important to be aware of this phenomenon, as a phantom shock may either represent or contribute to the patient’s maladjustment to the ICD.

In one study about 1 in 10 patients with an ICD experienced phantom shocks and another proposed that patients with phantom shocks are more likely to be clinically depressed and have higher levels of anxiety than other ICD patients, regardless of history of actual shocks.

Shock Storm

A “Shock Storm” is defined as the occurrence of three or more distinct episodes of VT and/or VF within a 24 hour period, either resulting in a device intervention or monitored as a sustained VT (≥30 seconds). Some authors have set an arbitrary 5 min interval between VT/VF episodes to define a “storm”. It should be noted that the prevalence of shock storms is more common in those who have an ICD after a cardiac arrest (secondary prevention) as opposed to those who have it implanted before a cardiac arrest (primary prevention).

What should I do after I receive a shock?

Receiving a shock can be an unsettling experience and responses can vary widely. Advance knowledge of what to do and how to respond in this situation can be very helpful and so we have a page on this…

See our guide on How to Respond to an ICD Shock for more on what to do

Will my ICD clinic know if I’ve been shocked?

Your doctor will know if you receive a shock as the ICD records and stores data when therapy like a shock is delivered.  If you have a home monitor it will inform the ICD on the next upload either automatically or manually if you request it.

What happens if someone if is touching me when I get an ICD shock?

If someone is touching you when your ICD delivers a shock, they may feel a slight tingling sensation which is not dangerous for them. You may ‘jump’ or ‘cry out’ when you feel the shock and this may frighten people who are with you. It is important that they stay calm, stay with you and reassure you. Relatives and friends need to know that it is safe for them to be there, and also that, if you do get an electrical shock, it can be very comforting for you to have them there with you. Give your friends and relatives the phone number of your ICD clinic so that they will know who to contact if they are with you when your ICD delivers a treatment.

What if I’m Driving When I Get a Shock

If you feel there is a chance of being shocked whilst driving you should stop as soon as it is safe to do so.  If you have a history of passing out from ICD shocks this may mean taking immediate action.  If you receive an appropriate shock (at any time) you should contact the DVLA and surrender your license and cease driving for 6 months minimum. Depending on the situation and consultation with your doctor the suspension period may also be longer. 

See our guide on Driving and The DVLA for more information

Plan for Shocks

The ICD’s job is to provide lifesaving therapy to your heart. This therapy can sometimes require a shock. You need to have a plan for you and your family to respond in the event of a shock. Explain to them what to look for when it happens and how they can help you i.e. do an upload on your home monitor, know the ICD clinic number.  Having a supportive team with you can make an enormous difference in staying positive after the shock.  Practice deep breathing and relaxing responses to help you to stay calm when shock occurs. Becoming hyper-aroused (such as panicking, shallow breathing, etc.) can escalate the impact unnecessarily. Some people recommended meditation as a daily action to help you stay mindful of your reactions to stressful situations.

See our guide on How to Respond to an ICD Shock for more on planning


If you are on any medications of a heart condition then it is likely that they will lessen the chance of you ever having a shock, it is therefore important that you maintain a good regime of taking your medications as prescribed. If you receive an appropriate shock your doctor may consider altering your medications to lessen the chance of reoccurrence.

Psychological Responses

Seek professional help for psychological responses to ICD shock. It is normal to feel anxiety or depression, worry and fear with respect to an ICD shock. These psychological effects are often associated with the uncertainty of when a shock will appear or what the outcome of it might be (including fear of death). These fears will slowly decrease as you get more used to your ICD but it’s important to get help through talking to people who can reassure you.


Engaging in regular moderate aerobic exercise can offer significant benefits to individuals with ICDs. Contrary to concerns about exercise triggering shocks, research indicates that appropriately tailored exercise regimens can improve cardiovascular health without elevating the risk of receiving shocks from the device. Exercise promotes heart health, enhances overall cardiovascular function, and helps in maintaining a healthy weight, which collectively contribute to reducing the likelihood of arrhythmias that might trigger ICD therapies. It’s important for individuals with ICDs to collaborate with their healthcare providers to develop exercise plans that suit their specific needs and conditions. By following a well-designed exercise routine, individuals can foster long-term heart health while minimising the risk of shocks, thereby promoting a better quality of life and overall well-being.

Florida Shock Anxiety Scale

The Florida Shock Anxiety Scale (FSAS) is a valuable tool designed to assess the levels of shock-related anxiety experienced by individuals with ICDs. This scale aids in understanding the psychological impact of living with the possibility of receiving shocks from the device. It comprises a set of questions that gauge aspects such as worry, emotional distress, impact on daily life, and coping mechanisms related to ICD shocks. High scores may indicate a need for additional psychological support. By addressing both physical and psychological aspects, the FSAS contributes to a more comprehensive approach in providing care and support for individuals with ICDs.

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