Although the insertion of an ICD usually requires only minor surgery, it still carries some risks. While complications are rare, patients should report any of the following symptoms immediately:

Serious complications from the surgery occur in less than 1 percent of cases. These include:

• Severe bruising or bleeding
  
• Formation of a blood clot
  
• Torn blood vessel
  
• Punctured lung or heart muscle
  
• Stroke
  
• Heart attack
  
• Introduction of air into the space between the lung and chest wall
  
• Inappropriate shock. When a shock is delivered in absence of arrhythmias due to device malfunction or oversensing.
  
• Death

The risk of having one of these complications is increased if people have certain characteristics, such as:

• Advanced age
  
• Obesity (body mass index 30 or greater)
  
• Severe lung disease (often due to smoking)
  
• Use of various medications
  
• Severely decreased heart function

Rarely, there may also be some complications with the ICD itself. As with any mechanical device, the ICD or the wires may malfunction. A small percentage of patients report at least one time in which the ICD delivered a shock when no arrhythmia was present. If patients feel a shock from the ICD, they should call their physicians. If other symptoms occur, such as dizziness, clamminess, palpitations, angina (chest pain), loss of consciousness or blackouts, patients are advised to call an ambulance and go to the emergency room. These symptoms indicate that their ICD may need reprogramming.

Some patients may sustain a cluster of episodes of ventricular tachycardia and/or ventricular fibrillation that results in multiple shocks (discharges) by the ICD. This is known as an “electrical storm.” An electrical storm is when at least three shocks and/or anti-tachycardia pacing signals are delivered within 24 hours. ICD patients surviving an electrical storm have an increased risk of death, particularly within the first three months following the event. What precisely causes electrical storms is not known, but patients experiencing them tend to have ventricular tachycardia and an ejection fraction below 30 percent. They are also less likely to have undergone revascularization (e.g., coronary bypass). Patients who feel multiple discharges in a short time period should contact their physician, who will review the data recorded by the ICD and consider appropriate treatment.