One of the main causes of chest pain is a blockage of blood flow down the coronary arteries, the blood vessels that deliver oxygenated blood to our heart muscle to allow it to beat. Depending on how fast the blockage forms, it is labeled as either a stable or unstable blockage.

Unstable blockages occur quickly when an atherosclerotic plaque ruptures within the coronary artery and a clot forms on top of it. The clot, along with the plaque, can obstruct blood flow, deprive heart muscle of oxygen, and lead to a heart attack. This is called an acute coronary syndrome, and it frequently requires a minimally invasive procedure called a cardiac catheterization to diagnose the blockage and then provide options to treat it.

When the buildup of plaque in the coronary arteries occurs gradually, most patients have little to no symptoms. As the blockage expands over time, patients can experience chest pain with activity that usually goes away with rest. When a blockage causes this predictable pattern of chest pain, it is called stable coronary artery disease (CAD). A cardiac catheterization may or may not be needed to manage stable CAD.

Stress tests

A stress test can be used to determine the likelihood of having a coronary artery blockage. The main goal of the test is to see how your heart works during physical activity. Because exercise makes your heart pump harder and faster, an exercise stress test can reveal problems with blood flow within the coronary arteries. Certain types of stress tests can even detect how much of the heart has ischemia, or inadequate blood supply.

A stress test usually involves walking on a treadmill or riding a stationary bike while your blood pressure, heart rate and rhythm, and symptoms are closely monitored. (Some patients are given medications that imitate the effects of exercise because they are unable to exercise.) Depending on the type of stress test, some patients are given a radioactive tracer to help create an image of how well blood is reaching different parts of their heart muscle, both during exercise and while at rest, to detect ischemia. If the stress test is abnormal, patients may need cardiac catheterization to confirm the presence of any potential blockages, and possibly even undergo invasive treatment of them.

What is cardiac catheterization?

Cardiac catheterization is a diagnostic procedure that involves taking a long, thin tube called a catheter and threading it within an artery in the arm or leg to get to the coronary arteries. The coronary arteries are then injected with contrast dye to look for blockages.

Depending on the location and severity, the blockages can be treated with medications alone; with angioplasty plus stent placement (expanding a balloon located at the end of the catheter to open the blockage and placing a stent), which can be done during the cardiac catheterization procedure; or with open-heart surgery to reroute blood around the blockage (coronary artery bypass surgery, or CABG).

Studies have shown that cardiac catheterization, followed by angioplasty and stenting or CABG, can improve survival and decrease heart attacks in patients with acute coronary syndromes. But what are the benefits of cardiac catheterization in stable CAD?

Cardiac catheterization or medications only to treat stable CAD?

An older trial, known as the COURAGE trial, found that in patients with stable CAD, stenting plus medication therapy did not reduce the risk of death, heart attack, or other major cardiovascular events compared to medication therapy alone. However, stenting did provide symptom relief much quicker than medication therapy alone.

More recently, the ISCHEMIA trial, published in the New England Journal of Medicine, examined a subset of stable CAD patients with moderate to severe ischemia on stress testing. The researchers compared outcomes in patients who underwent cardiac catherization, along with angioplasty with stenting or CABG when feasible, plus medications, to patients who received medication therapy alone. The study found that there was no difference between the two groups in the primary endpoint (a combination of death from cardiovascular causes, heart attack, cardiac resuscitation, or hospitalizations for unstable chest pain or heart failure).

The ISCHEMIA trial did find that there was a small increase in procedural heart attacks (damage to the heart muscle caused by an interruption in blood flow to the heart during the procedure) in patients who underwent cardiac catheterization. But there was an even greater increase in spontaneous heart attacks in patients who did not undergo cardiac catheterization. The study also found that patients who underwent cardiac catheterization had more symptom relief than medication therapy alone.

The bottom line

The ISCHEMIA trial failed to show an outright benefit of cardiac catheterization (along with angioplasty with stenting or CABG when feasible, plus medications), compared to medications alone. As a result, treatment guidelines continue to recommend that all patients with stable CAD should first have their medications increased to maximally tolerated doses. However, cardiac catheterization would be very appropriate if such patients continue to have unacceptable symptoms, have poor tolerance to their medication therapy, or both.

Follow me on Twitter @DrDarshanDoshi

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