An Implantable Cardioverter-Defibrillator (ICD) is a medical device that continuously monitors heart rhythm. Surgically placed under the skin, often near the collarbone, with wires extending to the heart, its primary function is to detect and correct life-threatening rapid heart rhythms (arrhythmias) by delivering electrical impulses or shocks. While effective in preventing sudden cardiac arrest, experiencing a shock can be startling. Knowing the appropriate steps when an ICD activates is important for patient well-being.
What a Defibrillator Shock Feels Like
The sensation of an ICD shock is generally described as an intense, sudden experience. Some report a feeling similar to a quick thump or jolt in the chest, while others describe it as a powerful kick or punch that can cause the body to jump involuntarily. Though brief, typically lasting only a second, its intensity can be frightening. It is not uncommon to feel lightheaded or even momentarily lose consciousness just before or during a high-energy shock.
Immediate Steps During and After a Single Shock
If you feel your ICD about to deliver a shock, or if it has just delivered one, sit or lie down immediately. This prevents injury from lightheadedness or sudden muscle contraction that could lead to a fall. If standing, move away from objects that could cause harm if you lose balance.
After a single shock, remain calm and rest for a few minutes. Pay close attention to how you feel, noting any symptoms experienced before or after, and record the exact time it occurred. A single shock often indicates the device functioned as intended, successfully correcting a potentially dangerous heart rhythm.
Responding to Multiple Shocks
Receiving multiple shocks from an ICD within a short timeframe, such as over a few minutes or hours, signals a persistent heart rhythm issue. This means the device is actively working to control a recurring or unstable rhythm, and immediate medical attention is necessary.
If you experience multiple shocks, lie down and remain as still as possible. Have someone call emergency services, such as 911, immediately. If alone, contact emergency services yourself. This indicates a need for urgent medical assessment to understand the underlying cause and stabilize your condition.
When to Seek Medical Attention
Seek medical attention after an ICD shock based on circumstances and symptoms. Call emergency services immediately if you receive multiple shocks, lose consciousness, experience severe chest pain, or have difficulty breathing. Immediate medical help is also warranted if you feel unwell after a single shock.
Even after a single shock where you feel fine, contact your cardiologist or device clinic promptly, typically within 24 hours. This allows your medical team to remotely access and review device data, providing valuable information about the heart rhythm event that triggered the shock. This assessment helps determine if medication or device setting adjustments are necessary. Regular follow-up appointments are also important for ongoing device monitoring, even without shocks.
Understanding Why the Device Activated
ICD activations are categorized as “appropriate” or “inappropriate” shocks. An appropriate shock occurs when the device correctly identifies a life-threatening arrhythmia, such as ventricular tachycardia or ventricular fibrillation, and delivers a shock to restore a normal rhythm. In these instances, the device has performed its intended, life-saving function.
Inappropriate shocks happen when the ICD activates for a non-life-threatening rhythm or due to misinterpretation of electrical signals. This can occur if the device mistakes a very fast normal heart rate, such as during strenuous exercise, for a dangerous arrhythmia. External electrical interference or device lead issues can also cause an inappropriate shock. While distressing, these shocks are not uncommon and can often be addressed by adjusting the ICD’s programming or medications after data analysis.