Stress Testing and Heart Disease Symptoms Janet V. Hays MD, FACC, FASE, FASNC Charles Conrad Brown and Anna Sahm Brown Distinguished Professor in Cardiovascular Disease Clinical Professor of Medicine, Division of Cardiology UT Health San Antonio hays@uthscsa.edu

Heart Disease Symptoms Heart Failure = The heart cannot pump enough blood around to meet the needs of the body Shortness of breath, fluid buildup, fatigue Rhythm Problems = Problems with the electrical stability of the heart Palpitations, dizziness, fainting Ischemia = Insufficient blood flow to the heart muscle relative to the work it has to perform Chest Discomfort = Angina

Angina: not always Pain, and not always in the Chest Classic: pressure, heaviness of left chest and left arm Sometimes burning, numbness Jaw, neck, back, arm, stomach discomfort Shortness of breath Indigestion Fatigue, weakness, dizziness, palpitations

Angina or Heart Attack?

Types of Angina Vasospastic Angina Stable Exertional Angina Fixed blockage of the coronary artery from cholesterol buildup. Symptoms occur predictably at a certain heart workload, and go away with rest. Over time, blockage gets worse and symptoms occur earlier. Too much demand for too long can cause a heart attack. Unstable Angina A previously stable blockage now becomes unstable and… Attracts clotting factors. Symptoms come and go, no longer just with activity. Unpredictable Very likely the vessel will totally block off, and cause a heart attack soon. Vasospastic Angina No underlying blockage, but … The vessel wall clamps down and squeezes off blood flow. Unpredictable If prolonged, can cause a heart attack... Stress tests are used to evaluate stable exertional ischemia.

Workload Needed to Provoke Demand Ischemia Depends on age, heart rate, blood pressure, and the level of exercise achieved. At a minimum, need to reach 85 % predicted maximal target heart rate for age. The best test is exercise to the point of severe fatigue, or reproduction of symptoms. 0.85 (220 - Age) = target heart rate example : 50 year old: target is 145

Types of Stress Tests Regular Exercise Stress Test: treadmill or bike Exercise Stress Test with Imaging: used when there are problems interpreting the EKG --with echocardiogram --with nuclear imaging Chemical Stress Test: for the person who cannot safely exercise to the level needed --must be combined with imaging --echo, nuclear, MRI, or PET

Exercise Stress Test Highly Preferred Most important information: EKG changes with increasing workload on the heart Much other information: --overall exercise level, degree of fitness --reproduction of symptoms --amount of workload required to cause ischemia --Heart rate, Blood Pressure response --Abnormal heart rhythms provoked by exercise

Abnormal EKG Changes with Exercise Looking for depression of the baseline of the EKG tracing; has to meet certain criteria to be considered positive.

EKG Changes Unfortunately, some EKGS are baseline abnormal or uninterpretable. Other EKGs develop borderline changes. Neither positive or negative

Exercise With Imaging Ordered if the baseline EKG is not interpretable, or if the exercise EKG is not clearly normal. Exercise echo: First obtain resting ultrasound images of the heart. Immediately after exercise, obtain images of the heart again. Looking for areas of the heart muscle that stop contracting due to inadequate blood flow. Sounds simple, but technically difficult to do well. Have to have good images, good exercise level, great tech. wall motion changes are a late finding and can go away quickly.

Nuclear Stress Test Imaging With exercise, or with chemical stress. Ordered when the EKG is not clearly normal, or when other types of images are not acceptable. Often the safest test to perform when there are other medical problems.

How does a Nuclear Stress Test work? A short acting radioactive isotope is injected, and is taken up preferentially by the heart muscle cells. The isotope stays there until it decays into its inactive form. While it decays, the isotope emits energy that is detected by the scanner, quantified, and ultimately displayed. Heart muscle areas light up in direct proportion to the amount of coronary blood flow received. Lots of computer processing. Isotope goes everywhere, designed to go preferentially to the heart

How does a Nuclear Stress Test Work? Areas with poor blood flow appear as defects relative to other areas. Defects present at rest suggest a prior infarct. By obtaining a scan at rest, and another scan during exercise, we can compare blood flow at rest and stress. Defects present at stress but not at rest suggest a high grade blockage of blood flow. Infarct or attenuation…

How does a Nuclear Stress Test work? Exercise causes blood flow to the heart to increase 2-3 fold. Computer processing makes the images easier to compare stress and rest images.

How Does a Chemical Nuclear Stress Test Work? One type, Dobutamine, is similar to exercise; it increases heart rate, blood pressure, and workload on the heart, to produce demand ischemia. Otherwise, a specific medicine is used that works on receptors on the coronary blood vessels to make them dilate (“vasodilator stress test”). IV Regadenoson (“Lexi”), adenosine, or dipyridamole increases blood flow in normal coronary vessels 4-5 times. However, a blocked vessel cannot dilate; therefore the heart muscle it supplies will look like it is getting less flow compared to the other areas. Chemical stress tests therefore usually produce relative ischemia, rather than actual ischemia.

Can a Stress Test be Positive Even if I Don’t Feel any Angina? YES!!!! Angina is a late occurrence; usually the images and EKG are already abnormal by that time. Or…some people never feel angina at all. Ischemic Cascade

Which Type of Stress Test is Better? Depends on the patient, their EKG, and their other medical problems. All stress tests are designed to detect demand ischemia from significant coronary blockages (at least > 50% blockage). Because we don’t want to miss a significant coronary blockage, stress tests are sometimes too sensitive, with some expected false positives. While a chemical nuclear stress test is often the safest test for the patient to undergo, it has more problems with “false positive” defects. Fuzzy images, with many potential artifacts.

Instead of this nice starting picture… Artifact Problems Instead of this nice starting picture… High loops of bowel can overlap the heart… And we get this

More Reasons for False Positives Or a patient has large breasts that attenuate the images…. Or the patient’s arm is in the way…. Breast implants Or the patient moves around too much during the study…

How Good is a Negative Stress Test? A normal, good quality stress test is very reassuring. The chance of a cardiac event in the near future is low. Even so, because not all coronary blockages are stable, not all angina (or heart attacks) can be predicted. False negatives are rare, but do happen. Common reason for a false negative: Inadequate stress and the patient did not reach the target workload….. Either due to inadequate exercise stres

Other Reasons for False Negatives Or…. the patient’s medications prevented an adequate rise in heart rate. Or…. for a Chemical Nuclear Stress Test: Caffeine!!! --Caffeine specifically blocks the receptors that the chemical works on. This is why we ask patients to hold their medicines and caffeine prior to a stress test… because we hate to cancel a test after the patient has arrived. Plus….the isotopes get wasted! Not to mention isotopes are expensive, and NOT locally produced. Currently $30-40 dollars per dose = $80 a day

Summary Angina: pressure, heaviness of left chest and left arm are classic, but many other symptoms are possible. Prolonged, more severe symptoms can be a heart attack (“if you are on your 3rd nitroglycerin, get to the ER….”). Classic Demand Angina: Symptoms that come on with exertion and go away with rest; this is what stress tests are looking for.

Summary Whenever possible, exercise as the stressor is best. Images (echo or nuclear) are often needed due to EKG changes. The “best test” varies per patient. Improper preparation does matter. Stress tests are designed to catch all problems, with very few false negatives, but some expected false positives. Sometimes more testing is needed.

Thank you for your Attention! Questions?