Dr. Keith Roach

DEAR DR. ROACH: I am an 81-year-old male who is in generally good health, except that I suffer from heart disease and acid reflux. My heart disease started in 1994 when I had three stents inserted, and I underwent an angioplasty in 1995 to have one of the stent ends opened up. In subsequent years, I received six more stents and another angioplasty for blockages over 90%. Most of these were in the right coronary artery.

In 2015, I had double bypass surgery as the left anterior descending artery was over 60% blocked, and the right coronary artery also had another 90% blockage. I have now found out that the bypasses are both about 75% blocked and have become calcified. My doctors concluded that the blockages took place rather soon after the bypass surgery. They have placed me on medication and plan to continue this until they are forced to do something else.

Despite all of this, I have never had a positive stress test. All of my stress tests, including a very recent one using nuclear medicine, came out negative. All of the procedures and surgery took place after I walked in and indicated that I was having pressure in my chest and back of my throat. How is this possible? Both of my cardiologists have learned to trust my judgement, rather than using the stress test. — Anon.

ANSWER: There are many kinds of stress tests. They are designed to look for blockages in blood flow due to a blood vessel being partially clogged, most commonly with cholesterol plaque. The heart has to be stressed (through exercise or a medication that makes the heart work harder) and imaged in some way. All stress tests include an EKG, and they can also include a radioactive dye or echocardiogram to look at wall motion under stress.

Stress tests largely rely on one part of the heart getting less blood than the rest of the heart. When part of the heart doesn’t get enough blood, the EKG has characteristic changes. Since less blood flows to that part, less dye will be seen in the affected part of the heart. If an echocardiogram is used, the affected muscle doesn’t contract as well as it should.

Unfortunately, there are times when stress tests fail to identify blockages. One common reason is when people have multiple areas of blockage (sometimes called “balanced ischemia”), so it isn’t just a singular part of the heart that is particularly affected. It can also be seen in people who have collateral circulation, when the body has made or enlarged existing blood vessels to get around a blockage. If the person doesn’t exercise enough to cause differential blood flow (or the dose of medicine is inadequate), the stress test may come out negative.

As many as 15% of negative stress tests are false negatives, meaning that there really are blockages, but the stress test comes out normal. A wise clinician recognizes that tests can give misleading information, so when their suspicion is high, despite a normal test, they will request an additional test, such as a coronary angiography or a CT angiogram of the heart.

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Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Dr., Orlando, FL 32803.