Stress Testing: What the Test Measures, What It Misses

The Scene

The following scene is drawn from the composite of patients I have cared for in clinic and on the hospital floor. All identifying details are changed.

He had been told, three years in a row, that his stress test was negative. Normal, reassuring, nothing to worry about. He took those words at face value. He continued eating the way he ate, did not start the statin his internist had mentioned once and then dropped, and did not return to cardiology because he had passed the test.

He was sixty-one years old when he presented to the emergency department with a proximal LAD occlusion. The interventional team opened the artery within 90 minutes. He survived. His ejection fraction dropped to 40 percent.

When I reviewed his prior records, I found three consecutive nuclear stress tests, each read as normal, and a calcium score from two years earlier that had not been ordered by his cardiologist. The calcium score was 387. His Agatston score had been sitting in a primary care note, unreferenced, while the nuclear scans were being used to reassure him.

This scenario is not rare. It reflects a misunderstanding of what stress testing measures that is widespread among patients and, frankly, not always corrected by the physicians ordering the tests.

Stress testing measures myocardial ischemia under conditions of increased demand. It asks: when the heart needs more blood than it gets at rest, does the supply fall short? A positive stress test means significant ischemia. A negative stress test means no significant ischemia at the level of exercise or pharmacologic stress achieved. It does not mean no plaque. It does not mean no risk. It does not mean the coronary arteries are clean.

Plaque causes ischemia only when it has narrowed the lumen by 70 percent or more in most territories. A patient with 40 to 60 percent stenosis in multiple vessels, extensive non-calcified plaque, and a calcium score of 387 may have a perfectly normal nuclear stress test because none of those stenoses are causing reduced perfusion at peak stress. The plaque is there. The risk is real. The test does not see it.

This is not a failure of stress testing. It is a failure of the question being asked. Stress testing was never designed to detect plaque. It was designed to detect ischemia. When used for the right question, in the right patient, it provides powerful prognostic information that directly guides management.

At Carle Foundation Hospital in Urbana-Champaign, the cardiac stress laboratory is integrated with the advanced imaging and cardiac catheterization program, allowing the full sequence from stress testing to coronary CTA to invasive angiography to be coordinated without the patient having to navigate multiple health systems.

What It Is

Stress testing is a family of related studies that share a common purpose: measuring the heart’s response to increased metabolic demand. The “stress” can be physiological (exercise) or pharmacological (vasodilator or inotropic drugs). The endpoint measured can be ECG changes (exercise ECG stress test), myocardial perfusion (nuclear stress test or CMR perfusion), or wall motion (stress echocardiography).

Exercise ECG stress test (standard stress test, “treadmill test”): The patient walks on a treadmill according to a standardized protocol, usually the Bruce protocol, while a 12-lead ECG is monitored continuously. Heart rate, blood pressure, and symptoms are recorded at each stage. The test is positive for ischemia if the ECG develops ST-segment depression of 1 mm or more in a horizontal or downsloping pattern, or if ST elevation occurs in a territory without prior Q waves.

Nuclear stress test (myocardial perfusion imaging, MPI): A radiotracer (technetium-99m sestamibi or tetrofosmin, or thallium-201) is injected at peak stress. The tracer distributes in proportion to myocardial blood flow. Images obtained with a gamma camera at stress and at rest are compared. A territory that shows reduced tracer uptake at stress but normal uptake at rest represents a reversible perfusion defect, indicating ischemia in a coronary territory. A territory that shows fixed reduced uptake at both stress and rest represents infarcted myocardium.

Stress echocardiography: Echocardiographic images are obtained at rest and at peak stress (or immediately after peak stress for treadmill protocols, or during each dobutamine infusion stage for pharmacologic stress). Regional wall motion abnormalities that develop during stress indicate ischemia in that territory. A normal stress echo shows uniform wall motion increase across all segments at peak stress.

CMR perfusion stress: First-pass gadolinium kinetics during adenosine or regadenoson infusion demonstrate territories of reduced perfusion. The highest spatial resolution of any perfusion imaging modality. Covered in PROC-012.

Each modality’s specific capabilities:

The Mechanism

Why exercise stresses the heart: At rest, myocardial oxygen consumption is modest. During peak aerobic exercise, cardiac output increases four to five-fold, heart rate increases, and myocardial oxygen demand rises sharply. To meet this demand, coronary blood flow must increase by three to five times the resting value, achieved primarily through vasodilation of the small resistance vessels (arterioles). A coronary artery stenosis of 50 to 70 percent does not limit resting flow, but may limit the vasodilatory reserve during peak demand, producing a supply-demand mismatch: ischemia.

The Bruce protocol: The Bruce protocol is the most widely used treadmill protocol in the United States. It begins at a speed of 1.7 mph and a 10 percent incline (Stage 1) and increases speed and grade every three minutes. Most patients reach maximum exertion at Stage 3 or 4 (8 to 12 minutes of Bruce protocol corresponds to approximately 10 to 13 metabolic equivalents, or METs). The test is continued until the target heart rate (85 percent of age-predicted maximum: 220 minus age) is achieved, or until symptoms, ECG changes, or hemodynamic criteria mandate stopping. Submaximal tests (heart rate below 85 percent target) have substantially lower sensitivity for ischemia detection.

Duke Treadmill Score: The Duke Treadmill Score (DTS) is a validated prognostic tool calculated from three components: exercise time in minutes on the Bruce protocol, ST deviation in millimeters, and exercise-induced angina (0 = no angina, 1 = angina present, 2 = angina causing test termination). The formula is: DTS = exercise time (minutes), (5 x ST deviation), (4 x angina index). Scores of 5 or above are low risk (annual MI or cardiac death rate below 1 percent). Scores of -11 or below are high risk (annual event rate above 5 percent). Intermediate scores (-10 to +4) warrant additional imaging 5 / Solid .

Pharmacologic stress: Patients who cannot exercise adequately (due to orthopedic limitations, peripheral artery disease, deconditioning, or inability to achieve target heart rate) require pharmacologic stress.

Vasodilators (adenosine, dipyridamole, regadenoson): These agents act on A2A adenosine receptors in the coronary arteriolar smooth muscle to produce maximal vasodilation, increasing coronary blood flow three to five-fold in normal vessels. Diseased vessels with a fixed stenosis cannot augment flow proportionally, creating a heterogeneity of perfusion that the nuclear or CMR tracer then images. These agents do not increase myocardial oxygen demand; they create flow heterogeneity by revealing the relative inability of stenotic vessels to vasodilate. They are the preferred agents for nuclear myocardial perfusion imaging.

Dobutamine: A synthetic catecholamine that increases heart rate and contractility, simulating the hemodynamic effects of exercise without requiring the patient to move. Used primarily for dobutamine stress echocardiography and dobutamine stress CMR. Dobutamine is the pharmacologic stress agent of choice when vasodilators are contraindicated (bronchospasm, caffeine ingestion) or when wall motion assessment (rather than perfusion) is the goal.

Why nuclear stress misses non-obstructive plaque: Nuclear myocardial perfusion imaging detects heterogeneity of perfusion. If a patient has moderate stenoses in all three major coronary territories simultaneously, the radiotracer distributes uniformly, appearing normal. This is the phenomenon of “balanced ischemia,” and it is one mechanism by which severe three-vessel disease can produce a false-negative nuclear scan. More commonly, the false-negative occurs because the stenoses present are simply not hemodynamically significant enough to limit flow during stress. The plaque is real. The ischemia test is genuinely negative. The conclusion that should be drawn is “no significant ischemia,” not “no disease.”

How It Is Used

Diagnostic use (symptomatic patients): Stress testing is appropriate for symptomatic patients with an intermediate pre-test probability of obstructive coronary artery disease who can exercise adequately and have an interpretable resting ECG. The ACC/AHA 2021 Chest Pain guidelines position exercise ECG as a Class I option for low-to-intermediate risk stable chest pain, and nuclear stress or stress echo as options when additional imaging information is needed or when the resting ECG is abnormal (left bundle branch block, LVH, ST changes, digoxin effect) that renders exercise ECG non-interpretable (Gulati, JACC. 2021; doi:10.1016/j.jacc.2021.07.053).

Prognostic use (known CAD): In patients with established coronary artery disease, stress testing provides prognostic data that guides medical therapy intensity and revascularization decisions. The extent of perfusion defect, the EF response to stress, and the presence of ST changes at submaximal workload are all prognostic markers.

ISCHEMIA trial context: The ISCHEMIA trial enrolled 5,179 patients with stable coronary artery disease and moderate-to-severe ischemia on stress imaging and randomized them to invasive strategy (coronary angiography with revascularization) versus conservative medical strategy. The key finding: no significant difference in the rate of death from cardiovascular causes or MI between strategies over a median 3.2 years (HR for invasive vs conservative: 0.90; 95% CI 0.82 to 0.99; overall p = 0.03 after adjustment for non-inferiority; but primary endpoint not significantly different in the 4-year ITT analysis) 5 / Solid . This trial established that moderate-to-severe ischemia on stress imaging, in stable patients, is not by itself an indication for revascularization. Symptoms and quality of life drive the revascularization decision. Risk factor improvement and medical therapy are non-inferior for long-term survival.

Pre-operative cardiac clearance: Stress testing before non-cardiac surgery is appropriate when the patient has active cardiac symptoms, a high-risk procedure is planned (major vascular surgery), and poor functional capacity (less than 4 METs) that cannot be assessed clinically. Routine stress testing before low-to-intermediate risk surgery in asymptomatic patients is not supported by evidence and adds cost without improving outcomes (Unsupported, Fleisher, JACC. 2014; doi:10.1016/j.jacc.2014.07.944).

Post-MI surveillance: Routine stress testing in asymptomatic patients after MI is not recommended by current guidelines. Stress testing after MI is appropriate when symptoms develop, when revascularization was incomplete, or when functional capacity assessment is clinically important.

The Evidence

Sensitivity and Specificity of Stress Testing Modalities

The performance characteristics of stress testing modalities for detecting obstructive coronary artery disease (greater than 50 percent stenosis on invasive angiography) vary by modality and patient population:

Exercise ECG:

• Sensitivity: approximately 68 percent (pooled across multiple meta-analyses)
• Specificity: approximately 77 percent
• Performance is substantially lower in women, patients with single-vessel disease, and those with submaximal exercise 5 / Solid 00481-7)

Nuclear SPECT:

• Sensitivity: 87 to 90 percent
• Specificity: 73 to 80 percent
• High negative predictive value (greater than 99 percent) for events in the following 12 months when perfusion is completely normal at adequate stress

Stress echocardiography:

• Sensitivity: 80 to 85 percent
• Specificity: 84 to 86 percent
• Operator-dependent; performance varies with echocardiographer and reader experience

CMR perfusion:

• Sensitivity: 89 percent
• Specificity: 87 percent (CE-MARC trial)
• Higher sensitivity than SPECT with equivalent specificity; no ionizing radiation 5 / Solid 61335-4)

The Prognosis of a Negative Nuclear Stress Test

A completely normal nuclear stress test with normal wall motion and normal EF response to stress carries an annual rate of major adverse cardiovascular events (MACE) of less than 1 percent in most registries 5 / Solid . This is the basis for the clinical utility of a negative stress test: when normal, it genuinely identifies a low-risk patient in whom further workup is not immediately necessary.

However, this prognosis applies to a 12 to 24-month window. The annual 0.5 to 0.7 percent event rate in patients with a normal stress test is still a meaningful cumulative risk over ten years, particularly in patients with established risk factors. A patient with diabetes, hypertension, LDL of 150 mg/dL, and a normal nuclear stress test has a normal stress test and a meaningful ten-year cardiovascular risk. Those are not contradictory facts.

ISCHEMIA Trial: What Moderate-to-Severe Ischemia Means

The ISCHEMIA trial directly tested the assumption that moderate-to-severe ischemia on stress imaging should drive revascularization. The trial’s finding, that invasive strategy did not reduce cardiovascular death or MI compared with intensive medical therapy over 3.2 years, has practical implications:

• Moderate-to-severe ischemia on stress imaging is a marker of disease severity and long-term risk, not an automatic indication for revascularization
• Revascularization in stable CAD provides angina relief, improved quality of life, and reduced procedural angina, but does not, based on current evidence, reduce MI or death in the short term compared with guideline-directed medical therapy
• Medical therapy improvement (statins, antihypertensives, antiplatelet therapy, lifestyle modification) is the primary intervention for stable ischemic heart disease

The ISCHEMIA-CKD substudy, conducted in patients with advanced CKD excluded from the main trial, showed similar results: no significant benefit of invasive strategy over conservative management 5 / Solid .

Exercise Capacity and Mortality

Exercise capacity measured in METs at stress testing is one of the strongest independent predictors of all-cause mortality, more powerful than most traditional cardiovascular risk factors. A landmark study of 6,213 men undergoing treadmill testing showed that each 1-MET increase in exercise capacity was associated with a 12 percent improvement in survival 5 / Solid . This relationship holds across age groups and in both sexes. The treadmill test does not just detect ischemia. It measures cardiorespiratory fitness, which is a direct physiological variable associated with longevity regardless of whether ischemia is present.

The Duke Treadmill Score in Clinical Practice

In a validation cohort of 613 patients, DTS identified three risk categories: low risk (DTS greater than 5; four-year survival 99 percent), intermediate risk (DTS -10 to +4; survival 95 percent), and high risk (DTS less than -11; survival 79 percent). Patients in the intermediate zone benefit from imaging-based risk stratification (nuclear stress or stress echo) to refine the risk estimate before decisions are made 5 / Solid .

Regadenoson vs Adenosine

Regadenoson (selective A2A agonist) administered as a single 0.4 mg IV bolus has equivalent diagnostic accuracy to adenosine continuous infusion for nuclear MPI 5 / Solid . Regadenoson is substantially easier to administer (no weight-based dosing, no pump), better tolerated (lower incidence of AV block and bronchospasm), and has become the dominant pharmacologic stress agent in the United States for nuclear perfusion imaging.

The Patient Experience

Standard Treadmill Stress Test

The patient arrives wearing comfortable walking shoes. No food or caffeine for four hours before the test. Medications are reviewed; beta-blockers may or may not be held depending on whether the test is for diagnosis (hold to allow target heart rate achievement) or risk stratification with known CAD (continue).

Twelve ECG electrodes are placed. A blood pressure cuff is applied. The treadmill begins at a gentle walk. Every three minutes the speed and incline increase. Most patients reach a point of significant exertion between 8 and 12 minutes. The test ends when target heart rate is achieved, when symptoms mandate stopping, when ECG changes appear, or when the patient requests to stop.

The post-exercise phase (cool-down) is critical. Many ischemic ECG changes appear in the first two to five minutes after stopping, not during peak stress. The patient walks slowly or rests while the ECG is monitored continuously for 8 minutes of recovery.

Nuclear Stress Test

For pharmacologic nuclear stress (the most common type), the preparation involves avoiding caffeine for 24 to 48 hours before the test. Caffeine blocks adenosine receptors and significantly attenuates the vasodilatory response to adenosine or regadenoson, blunting the perfusion heterogeneity that makes the test diagnostic. This is a point that needs explicit patient education because coffee is everywhere and patients often do not connect caffeine abstinence with cardiac testing.

The test involves two radiotracer injections (one at stress, one at rest), two sets of images (stress images and rest images), and total time in the imaging center of approximately 3 to 4 hours, though the actual radiotracer injections and image acquisitions take much less time than this. The long duration is because the rest and stress injections are typically separated by 2 to 4 hours.

Patients receiving regadenoson commonly experience flushing, shortness of breath, and chest heaviness lasting 30 to 90 seconds. These are expected physiological responses, not allergic reactions or signs of MI. Aminophylline reversal is available in the room.

What Your Cardiologist Will Not Have Time to Explain

• A “normal” nuclear stress test does not mean no coronary artery disease. It means no significant ischemia at the level of stress achieved. The calcium score is a separate question.
• Nuclear imaging involves ionizing radiation. Standard SPECT MPI delivers approximately 7 to 12 mSv depending on the radiotracer. This is a real dose in a patient who may have additional imaging over a lifetime. PET MPI delivers 2 to 5 mSv and is more accurate. Where PET is available, it should be the preferred modality.
• Exercise capacity reported as METs is a powerful prognostic variable independent of the ischemia result. Ask what your peak MET level was. A peak of 10 METs or above on the Bruce protocol is associated with excellent prognosis. A peak below 6 METs in a 55-year-old is a meaningful finding regardless of whether ischemia is detected.
• If your test was stopped before reaching 85 percent of age-predicted maximum heart rate without a diagnostic reason (symptoms, ECG change), the test is submaximal and its sensitivity for ischemia is substantially reduced.

Sex Differences

The exercise ECG stress test performs significantly worse in women than in men. Women have lower rates of obstructive CAD for a given chest pain presentation, meaning the false-positive rate for ST-depression is higher. Hormonal effects on the ST segment and lower absolute coronary artery size contribute to this. For this reason, imaging-based stress tests (nuclear or stress echo) are preferred over exercise ECG alone when stress testing is performed in women with chest pain. Nuclear MPI in women requires breast attenuation correction or prone imaging to avoid artifactual perfusion defects caused by breast tissue 5 / Solid .

Women also have a higher prevalence of microvascular angina (coronary microvascular dysfunction), which produces ischemic symptoms with normal epicardial coronary arteries on angiography and may produce normal nuclear perfusion imaging despite genuine ischemia. CMR perfusion imaging with absolute perfusion quantification may be more sensitive for microvascular disease in this population 4 / Promising .

Geographic Access

Nuclear stress testing is widely available in Illinois at both academic and community hospital settings. Carle Foundation Hospital in Urbana-Champaign operates a full nuclear cardiology laboratory with SPECT MPI and pharmacologic stress protocols. Advanced cardiac PET stress imaging (with quantitative flow reserve) is available at Northwestern Medicine Bluhm Cardiovascular Institute in Chicago, where rubidium-82 and N-13 ammonia PET protocols provide higher diagnostic accuracy with lower radiation dose than SPECT. University of Illinois Health and Rush University Medical Center offer nuclear and stress echo programs. Dobutamine stress echocardiography is available at all of these centers and does not require a dedicated nuclear facility.

Decisions and Trade-Offs

Exercise ECG vs Imaging-Based Stress: Which Is Appropriate?

Exercise ECG is appropriate when:

• The resting ECG is interpretable (no LBBB, no LVH with strain, no pre-excitation, no digoxin effect, no significant ST-T changes at rest)
• The patient can exercise to an adequate workload (at least 5 to 6 METs, ideally 85 percent of maximum predicted heart rate)
• The clinical question is primarily about exercise capacity and ischemia threshold in a patient with low-to-intermediate pre-test probability

Imaging-based stress is appropriate when:

• The resting ECG is non-interpretable
• The patient cannot exercise adequately
• Prior coronary revascularization (PCI or CABG) is present and localization of ischemia is needed
• Higher pre-test probability where a more sensitive test is needed
• The Duke Treadmill Score is intermediate on exercise ECG and functional imaging is needed to reclassify risk

Revascularization Versus Medical Therapy After a Positive Stress Test

The ISCHEMIA trial has substantially changed the conversation after a positive stress test. A positive nuclear stress test showing moderate-to-severe ischemia is not an automatic indication for catheterization and stenting. The first question is whether the patient has symptoms. An asymptomatic patient with a positive stress test and no significant angina should receive intensive medical therapy improvement before any invasive evaluation. A symptomatic patient with a positive stress test whose angina is not controlled on medical therapy is a candidate for invasive evaluation with possible revascularization for quality of life reasons 5 / Solid .

The exception is high-risk stress test findings that predict left main or proximal LAD disease: ST elevation in the recovery phase, widespread ST depression at low workload, severe perfusion defect in a large territory, stress-induced significant EF drop, hypotensive response to exercise. These findings warrant urgent invasive evaluation regardless of symptoms.

The Risk of Over-Reliance on a Normal Stress Test

The clinical instinct to reassure a patient with a normal stress test is understandable and is often clinically appropriate. But the reassurance should be calibrated. For a 40-year-old with mild hypertension and no family history presenting with atypical chest pain, a normal stress test genuinely provides two years of excellent negative predictive value. For a 60-year-old with a CAC of 400, LDL of 160, hypertension, and a family history of premature CAD, a normal nuclear stress test answers “no significant ischemia today” and nothing more. The risk factor burden, the calcium score, and the plaque biology are the determinants of the ten-year trajectory, not the current ischemia status.

The Three Questions Every Patient Should Ask

1. “What was my peak exercise capacity in METs, and what does that mean for my longevity?” Exercise capacity is one of the most powerful predictors of all-cause mortality. Ask for the MET value, not just whether ischemia was found. A 55-year-old achieving 12 METs on a Bruce protocol without ischemia has a different prognosis than one achieving 6 METs on the same protocol.

2. “If my stress test is normal, does that mean I do not have coronary artery disease?” The honest answer is no. A normal stress test means no significant ischemia at the level of stress achieved. It says nothing about non-obstructive plaque. If you have significant risk factors and a family history of premature MI, ask whether a coronary calcium score or coronary CTA would provide additional information beyond the stress test.

3. “If my stress test is abnormal, what specifically do you plan to do about it?” The answer should not be automatic catheterization. Ask whether the ischemia is causing symptoms, whether the risk is high enough to warrant invasive evaluation, and whether medical therapy improvement would be the first step per current guidelines.

Clinical Synthesis

Stress testing is the most widely performed cardiac test in the United States. It is ordered millions of times each year, often without clear specification of what clinical question is being asked. The result, a binary normal or abnormal, is then communicated to the patient in language that frequently implies more certainty than the test delivers.

This clinical framework approaches stress testing as one of several tools with complementary domains. For the question “Is this patient’s chest pain ischemic?” exercise ECG or nuclear stress is the appropriate starting point. For the question “Does this patient have coronary artery disease?” coronary CTA is more accurate. For the question “What is this patient’s ten-year cardiovascular trajectory?” no single test answers that; it requires a synthesis of stress test performance (especially MET level), calcium score, lipid and metabolic data, blood pressure trajectory, and behavioral risk factors.

A structured cardiovascular assessment collects the data from all of these domains. Patients who arrive with a history of normal stress tests and uncontrolled risk factors receive a composite picture: the ischemia data from the stress test, the anatomical data from available calcium scores or CTA, and the population-level risk calculation from validated models. Those three data streams are not always concordant, and the discordance is precisely the information that has clinical value.

For patients in whom stress testing has been repeatedly normal but risk factor burden remains high, a structured cardiovascular assessment identifies whether the appropriate complementary anatomical imaging has been obtained. For patients who have had a positive stress test followed by normal coronary angiography, the cardiovascular workup explores microvascular dysfunction as a diagnosis, which has its own treatment pathway.

A structured metabolic reset provides the structure for patients with stable ischemic heart disease post-ISCHEMIA-era who are pursuing medical management rather than revascularization. The medical therapy framework includes high-intensity statin, blood pressure improvement, antiplatelet therapy, lifestyle modification, and structured follow-up for symptom surveillance.

Cardiac stress laboratory services are available at Carle Foundation Hospital in Urbana-Champaign with same-day nuclear SPECT and exercise protocols. For patients requiring advanced cardiac PET stress testing or CMR perfusion imaging, referral pathways to Northwestern Medicine Bluhm Cardiovascular Institute and Rush University Medical Center are coordinated through the clinical network.

Paired Foundations Articles:

• PROC-011: Coronary CTA (anatomical complement to functional stress testing)
• PROC-012: Cardiac MRI (CMR perfusion alternative to nuclear stress)
• PROC-001: Cardiac Catheterization (invasive evaluation following positive or high-risk stress test)
• PROC-002: PCI (revascularization for symptomatic ischemia confirmed by stress testing)

The Signal Check is fifteen questions mapping the cardiovascular risk pattern across the physiological domains most commonly missed in standard screenings. It produces a specific starting point for your next clinical conversation.