What happens during cardiac catheterization?

There are two main types of cardiac catheterization:

• Right heart catheterization (venous or flow-directed catheter): The catheter is inserted through a vein in the groin region or at the elbow and then advanced to the right ventricle and the pulmonary artery. Flow-directed catheters have a small inflatable balloon at the tip, allowing them to be carried by the flow of blood. The catheter is used to measure the pressure levels in the right ventricle and the pulmonary artery. A contrast medium is injected through the catheter so that the right chamber, the circulation of blood and the function of the cardiac valves can be examined.
• Left heart catheterization (arterial catheter): This catheter is advanced through an artery in your groin region, elbow or wrist and into the heart’s left ventricle. After a contrast medium has been injected it’s possible to examine the left ventricle, the aorta, the circulation of blood and the performance of the cardiac valves.

Coronary angiography (an x-ray examination of the coronary arteries) is also possible with the commonly used left-heart catheterization procedure. Contrast medium is injected into the coronary arteries to find possible constrictions. Treatment can also be performed during the examination: If narrowed arteries (coronary artery disease, CAD) are found, they can be pushed open using a balloon affixed to the tip of the catheter. The catheter can also be used to implant a metal tissue support (stent) to keep the blood vessel open.

But coronary angiography (left heart catheterization) can't always find out whether a narrowed artery needs to be expanded. Measurements can then be done to see how affected the blood flow is in the narrowed section. A flexible wire with a built-in sensor is pushed through the catheter into the narrowed artery. The sensor measures the pressure before and after the narrowed section: The bigger the pressure difference is, the more affected the blood flow towards the heart is. The measured value is called the myocardial fractional flow reserve (FFR).

Tissue samples can also be taken during right heart and left heart catheterization. Doctors can also check possible causes of arrhythmia. Specialized catheters may be used to measure how much blood the heart pumps in one minute. This can help doctors find out whether the heart is performing poorly.

Cardiac catheterization is especially well-suited for the following situations:

• Symptoms such as chest pain or tightness and shortness of breath, or after a heart attack. Left heart catheterization can help to determine the location and severity of a possible narrowed coronary artery.
• Coronary artery disease: A narrowed or blocked blood vessel can be expanded with left heart catheterization. Blood flow at the narrowed section can be measured beforehand (FFR value).
• Suspected degenerative changes or dysfunction affecting the cardiac valves.
• Before heart surgery: If heart valve or bypass surgery is planned, the heart muscle tissue and the coronary arteries are checked for any abnormal changes using cardiac catheterization.
• For biopsies: Heart muscle tissue can be taken using a catheter in case of myocarditis (heart muscle inflammation).
• For an irregular heartbeat (cardiac arrhythmia).

Before starting the doctor first needs to know about any other medical problems you may have, such as diabetes, infections, bleeding disorders or allergies. It is also important to let the doctors know what medication you use (like anticoagulants, beta blockers or antidiabetics). A number of tests need to be completed before the procedure can be started:

• ECG
• Blood pressure measurement
• Blood testing: This serves to find out your blood count, and determine other parameters describing blood clotting ability and kidney and thyroid function. The latter is useful if a contrast medium containing iodine is injected.

Additional examinations ate sometimes done, possibly including a lung x-ray or an ultrasound of the heart (echocardiography).

The procedure is done in a catheterization laboratory (sometimes called a “cath lab”). Often the lab is in a hospital, but catheterization can also be done in an outpatient setting at a specialist clinic. You’re not allowed to eat anything for about six hours before the examination. The area of skin right at the insertion site in your groin region or on your arm may need to be shaved right before the procedure. You can be given a local anesthetic if you like.

The doctor punctures a blood vessel and then inserts the catheter to move it up to your heart. While this is done, the situation is monitored on a computer screen. Usually you don’t feel anything because the inside walls of the blood vessels aren’t sensitive to pain.

An x-ray contrast medium is injected through the catheter into the chambers of the heart and the coronary arteries to make them visible on the computer screen. This may feel warm for a short time. You may also feel temporary heart pain if one of the narrowed arteries is pushed open. This usually goes away as soon as the expansion is completed.

You can watch pictures of your own heart on the screen during the examination. The examination takes usually about 30 minutes. But it may also take much longer depending on what the doctors find and whether further measurements, expansion of the blood vessels or stent implantation are needed.

A pressure bandage is applied to the insertion site afterwards to prevent bleeding. Doctors will ask you to stay at the hospital another five hours for your own safety. You’ll need to continue to stay in a lying position for about four hours if the catheter was inserted in the groin region. And an additional two days of monitoring is usually required if a narrowed artery was detected and treated.

It is always important to rest at home for the first few days and avoid lifting heavy objects.

Cardiac catheterization is classified as a minimally invasive procedure, because no larger incisions are needed. It's considered to be a safe examination method: only about 1 out of 100 examinations results in complications. But if complications do occur, they can be severe – after all, it is a heart procedure. Because of this, your doctor must talk to you about the risks, possible consequences and alternative methods for examining your heart one day or more in advance of the procedure, unless it’s an emergency. After that you need to provide your written informed consent.

The risks include:

• Bleeding and bruising at the insertion site
• Allergic reaction to the contrast medium (ranging from itchy skin, swelling, or shortness of breath to circulatory shock)
• Usually temporary arrhythmia
• Blood vessel and nerve damage
• Acute heart attack or stroke

The risk of complications increases in people who already have severe cardiac disease or other related conditions.