August 2012 

Understanding sudden cardiac death

The heart is a large muscular pump that helps push blood around the body. The pumping action of the heart is driven by regular waves of tiny electrical currents. When disturbances in the electrical currents of the heart occur, heartbeats can become irregular and in some cases can even stop. When the heart stops beating and pumping blood the brain and lungs are immediately affected. People quickly become unconscious and, if standing, suddenly collapse and stop breathing. There is no pulse because the heart has stopped beating. This is called sudden cardiac death, or SCD.

Not a heart attack

Sudden cardiac death is different from a heart attack. In the latter condition, a blood vessel that brings oxygen-rich blood from the lungs to the heart becomes blocked, perhaps because of a large blood clot. During a heart attack, pain and distress occur yet the heart continues to beat. During SCD, the heart stops beating.

Sudden cardiac death usually occurs without a warning but in some cases the following symptoms may occur:

  • unexpected tiredness or lack of energy
  • fainting
  • dizziness
  • chest pain
  • shortness of breath

Changes in risk

In general, among HIV-negative people, the risk of SCD is generally very low (0.001% per year) in otherwise healthy teenagers and young adults. After the age of 30, the risk of SCD begins to rise and increases to about 0.1% per year. From this point, the risk gradually increases with age. In people with serious heart disease who are 50 or older, the risk of SCD may be much greater, reaching between 10% and 25% per year.

Focus on the heart

Disturbances in the heart’s electrical system are likely to occur in people who have or have had the following conditions:

  • heart attack
  • coronary artery disease
  • abnormally thickened heart muscle (cardiomyopathy)
  • abnormal heart valves
  • inherited heart disease
  • problems with the electrical system of the heart

As sudden cardiac death is linked to cardiovascular disease (CVD), the same factors that place a person at risk for CVD also increase the risk for SCD, as follows:

  • a family history of cardiovascular disease
  • smoking tobacco
  • higher-than-normal blood pressure
  • abnormal levels of cholesterol in the blood
  • obesity
  • diabetes
  • insufficient exercise
  • excessive intake of alcohol
  • age – SCD risk increases with age, particularly among men over the age of 45 and women over the age of 55
  • gender – men are between two and three times more likely to experience SCD
  • use of stimulants – cocaine and crystal meth
  • hyperthyroidism
  • an imbalance of nutrients such as potassium and magnesium


In cases of SCD, the flow of oxygen-rich blood to the brain stops and a person immediately loses consciousness. Unless the heart quickly resumes its normal rhythm and beats within about 10 minutes, the oxygen-starved brain undergoes serious damage and death occurs. People who survive SCD may show signs of brain damage.


A common test to monitor heart rhythms is the ECG—electrocardiogram (commonly called a cardiogram). For this non-invasive test, technicians place sensors on the chest and limbs and the ECG can detect abnormalities in the electrical wave produced by the heart.

To find the underlying cause of SCD there are many additional tests that a cardiologist may order, including analyses of blood samples, ultrasound and other scans of the heart and its vessels, and more complex tests of the heart’s electrical system. Some tests and procedures used in assessing the risk for SCD and heart disease may be invasive.

Preventing SCD

To help prevent SCD, regular checkups with a focus on screening for heart disease are necessary.  Leading a life that is good for your heart is also crucial. For more tips about how to do this, see CATIE’s in-depth Fact Sheet on heart health.


If a person has a high risk for abnormal heart rhythms or has abnormalities of the heart’s electrical system, cardiologists may prescribe drugs. Classes of drugs used to treat abnormal heart rhythms include the following:

  • beta blockers
  • ACE (angiotensin-converting enzyme) inhibitors
  • calcium channel blockers

In some cases, a tiny device called an implantable cardioverter defibrillator (ICD) may be surgically emplaced near the collarbone. The ICD has wires that are connected to the heart. The purpose of the ICD is to monitor the heart’s rhythms. It can release tiny electrical signals that adjust the heart’s rhythm.

As part of the assessment of the underlying cause of abnormal heart rhythm, if blood vessels that supply the heart with oxygen-rich blood narrow or are blocked, cardiologists may perform coronary angioplasty. In this procedure, a long, thin, flexible tube is inserted into an artery. The end of the tube can inflate like a very small balloon. This opens up the artery. Doctors may also insert a small tube (called a stent) to keep the artery open on a longer basis.

Other surgeries may be performed, including the following:

  • coronary bypass surgery
  • heart surgery to correct any inherited abnormalities
  • heart transplant