Residency · Residency · Cardiology

Stable Ischemic Heart Disease

Pathophysiology and Risk Assessment

Mechanisms of Chronic Myocardial Ischemia

The pathophysiology of stable ischemic heart disease encompasses several distinct mechanisms that reduce myocardial oxygen supply relative to demand. Fixed epicardial coronary stenosis represents the classic substrate, becoming flow-limiting at rest when the luminal diameter is narrowed by 90% or more, and during exercise or pharmacologic stress when the narrowing reaches 70% or greater, with a lower threshold of 50% or more for left main coronary artery disease. The concept of coronary flow reserve, defined as the ratio of maximal to resting coronary blood flow, provides a more physiologically integrated assessment. Normal coronary flow reserve is 2.5 or greater, while an impaired value below 2.0 independently predicts adverse cardiovascular events regardless of the degree of epicardial stenosis.

Coronary microvascular dysfunction has emerged as a critically important mechanism, characterized by impaired microvascular dilatory capacity despite angiographically non-obstructive epicardial arteries. This entity affects 30 to 50% of patients presenting with angina and non-obstructive coronary artery disease, and is more prevalent in women, patients with diabetes mellitus, and those with heart failure with preserved ejection fraction. Endothelial dysfunction, manifested as impaired nitric oxide-mediated vasodilation, contributes to both coronary microvascular dysfunction and epicardial vasospasm, representing a shared pathophysiologic pathway. Dynamic coronary obstruction represents yet another mechanism and includes vasospasm, as seen in Prinzmetal angina, and myocardial bridging, wherein systolic compression of the coronary artery occurs most commonly in the mid-left anterior descending artery territory.

Risk Factor Modification -- Foundation of Therapy

The cornerstone of managing stable ischemic heart disease lies in aggressive modification of cardiovascular risk factors. Hypertension should be targeted to less than 130/80 mmHg per the 2017 ACC/AHA guidelines, with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers serving as first-line agents in patients with established coronary artery disease. Diabetes management should target a hemoglobin A1c below 7% for most patients, with sodium-glucose cotransporter 2 inhibitors and glucagon-like peptide 1 receptor agonists preferred because of their cardiovascular benefits independent of glucose lowering, as demonstrated in the EMPA-REG OUTCOME, LEADER, and SUSTAIN-6 trials.

Dyslipidemia management requires high-intensity statin therapy for all patients with stable ischemic heart disease, with a low-density lipoprotein cholesterol target below 70 mg/dL, and ideally below 55 mg/dL per European Society of Cardiology recommendations. Smoking cessation represents the single greatest modifiable risk factor, reducing cardiovascular mortality by 36%, and should be supported with pharmacotherapy including varenicline, nicotine replacement therapy, or bupropion. Obesity and metabolic syndrome are addressed through weight management, adoption of a Mediterranean diet, and structured exercise programs. All patients with coronary artery disease should be referred for cardiac rehabilitation, with a target of 150 minutes per week of moderate aerobic exercise.

Diagnosis and Non-Invasive Testing

Pre-Test Probability

The diagnostic approach to stable ischemic heart disease begins with assessment of the pre-test probability of obstructive coronary artery disease. The 2019 ESC guidelines introduced a simplified pre-test probability model based on age, sex, and symptom character. Patients with a low pre-test probability of less than 5% generally require no testing and can be reassured with consideration of non-cardiac causes of symptoms. Those in the intermediate range of 5 to 15% should be considered for either functional or anatomic testing. Patients with a high pre-test probability exceeding 15% warrant functional or anatomic testing, with direct referral to coronary angiography reserved for those with very high pre-test probability or high-risk clinical features.

Stress Testing

Multiple stress testing modalities are available, each with specific advantages and diagnostic performance characteristics. Exercise electrocardiography, or treadmill testing, offers a sensitivity of approximately 68% and specificity of approximately 77%, making it best suited for intermediate-risk patients who can exercise and have an interpretable baseline electrocardiogram. This modality remains the lowest-cost and most widely available option. A positive test is defined by 1 millimeter or more of horizontal or downsloping ST-segment depression. The Duke Treadmill Score provides additional prognostic information, calculated as exercise time in minutes minus five times the maximum ST deviation in millimeters minus four times the exercise angina index. A score of negative 11 or below indicates high risk with an annual mortality exceeding 5%, while a score of 5 or above indicates low risk with annual mortality below 1%.

Stress echocardiography, performed with exercise or dobutamine, achieves higher diagnostic accuracy with a sensitivity and specificity of approximately 85% each, and offers the advantage of identifying and localizing regional wall motion abnormalities induced by ischemia. Stress cardiac magnetic resonance imaging, using dobutamine or vasodilator protocols, provides the highest diagnostic accuracy among non-invasive modalities, with a sensitivity of approximately 89% and specificity of approximately 87%, while simultaneously assessing perfusion defects, wall motion abnormalities, and myocardial scar through late gadolinium enhancement.

Nuclear myocardial perfusion imaging with single-photon emission computed tomography or positron emission tomography achieves a sensitivity of approximately 87% and specificity of approximately 73%. The distinction between fixed defects representing scar and reversible defects indicating ischemia is fundamental to interpretation, and positron emission tomography is superior to single-photon emission computed tomography for quantitative coronary flow reserve measurement. Vasodilator stress agents such as adenosine, regadenoson, and dipyridamole are used for patients unable to exercise, creating flow heterogeneity between normal coronary territories that can dilate in response to the vasodilator and stenotic territories that are already maximally dilated at baseline and cannot augment flow further. Positron emission tomography coronary flow reserve provides a quantitative measure that integrates both epicardial and microvascular function, with a value below 2.0 predicting adverse events regardless of anatomic findings on angiography.

Coronary CT Angiography (CCTA)

Coronary computed tomography angiography has established itself as a powerful diagnostic tool for suspected coronary artery disease, with a sensitivity exceeding 95% and specificity of approximately 85% for detecting significant stenoses. Its exceptionally high negative predictive value, exceeding 99%, makes it an excellent test for ruling out coronary artery disease in patients at low to intermediate risk. The landmark SCOT-HEART trial demonstrated that a CCTA-based diagnostic strategy clarified diagnosis, led to more appropriate treatment decisions, and reduced the incidence of myocardial infarction at 5 years of follow-up.

CT-derived fractional flow reserve represents a significant technological advance, applying computational fluid dynamics to standard CCTA datasets to identify hemodynamically significant stenoses without the need for invasive catheterization. Validation in the PLATFORM and NXT trials has demonstrated its ability to reduce unnecessary invasive angiography. Coronary artery calcium scoring serves as a powerful predictor of future cardiovascular events. A calcium score of zero is associated with a very low 10-year event rate of less than 1%, while a score exceeding 400 indicates high risk. This tool is particularly useful for asymptomatic risk stratification but is not appropriate for symptomatic patients, as it does not directly assess the degree of coronary stenosis.

<image> A comprehensive stress testing decision algorithm for suspected stable ischemic heart disease. Start with "Suspected SIHD: chest pain / anginal equivalent" at top. Step 1: "Calculate Pre-Test Probability (age, sex, symptom type)" with three branches. Low PTP (<5%): "No testing; reassure; consider non-cardiac causes." Intermediate PTP (5-15%): branches to "Can patient exercise?" → Yes: "Exercise stress echo or exercise nuclear (preferred over exercise ECG alone for diagnostic accuracy); Exercise ECG acceptable if ECG interpretable and no imaging needed." → No: "Pharmacologic stress imaging (dobutamine echo, vasodilator nuclear/MRI)." And "Anatomic testing alternative: CCTA (especially if low-intermediate PTP, young patient, desire to rule out CAD)." High PTP (>15%): "Functional imaging test (stress echo, nuclear, MRI) OR proceed directly to invasive angiography if very high risk features." Bottom box: "High-risk findings on any test warranting catheterization: large/multiple perfusion defects, stress EF drop, extensive wall motion abnormalities, significant LM or proximal LAD disease on CCTA, Duke treadmill score <= -11." Use green/yellow/red color coding for risk levels. </image>

Medical Therapy -- Anti-Anginal Agents

Beta-Blockers

Beta-blockers constitute the traditional first-line anti-anginal therapy, exerting their beneficial effects through reduction of heart rate, contractility, and myocardial oxygen demand, while simultaneously prolonging diastolic filling time to improve subendocardial perfusion. Commonly used agents include metoprolol succinate, bisoprolol, carvedilol, atenolol, and nadolol, titrated to achieve a resting heart rate of 55 to 60 beats per minute. In the post-myocardial infarction setting, beta-blockers carry a proven mortality benefit, particularly in patients with heart failure with reduced ejection fraction. However, the role of beta-blockers in stable ischemic heart disease without prior myocardial infarction or heart failure has been called into question. Data from the CLARIFY registry demonstrated that beta-blockers were not associated with mortality reduction in this population, prompting some guidelines to de-emphasize routine use in the absence of a clear indication beyond angina control.

Calcium Channel Blockers

Calcium channel blockers are classified into two major categories with distinct pharmacologic profiles. Dihydropyridine agents such as amlodipine and nifedipine extended-release exert their anti-anginal effects primarily through vasodilation and afterload reduction, though reflex tachycardia may occur and can be offset by combining with a beta-blocker. Non-dihydropyridine agents including verapamil and diltiazem provide rate-slowing effects and serve as alternatives to beta-blockers when the latter are not tolerated. The combination of non-dihydropyridine calcium channel blockers with beta-blockers should be avoided due to the risk of severe bradycardia. Calcium channel blockers are particularly effective for vasospastic angina, with verapamil and diltiazem preferred for this indication.

Nitrates

Nitrate therapy provides both acute symptom relief and chronic angina prevention through venodilation that reduces preload, modest arterial dilation, and epicardial coronary vasodilation. Short-acting nitroglycerin, administered as sublingual tablets or spray, is used for acute symptom relief. Patients should be instructed to sit before use, may repeat up to three times every 5 minutes, and should seek emergency care if symptoms do not resolve. Long-acting preparations, including isosorbide mononitrate at doses of 30 to 120 mg daily and isosorbide dinitrate, provide chronic angina prevention. A critical principle of nitrate prescribing is the provision of a nitrate-free interval of 8 to 12 hours daily to prevent the development of tolerance. Contraindications to nitrate use include concurrent phosphodiesterase-5 inhibitor use, with mandatory washout periods of 24 hours for sildenafil and vardenafil and 48 hours for tadalafil, as well as severe aortic stenosis, hypertrophic obstructive cardiomyopathy, and hypotension.

Ranolazine

Ranolazine represents a mechanistically distinct anti-anginal agent that inhibits the late sodium current, thereby reducing intracellular calcium overload during ischemia without affecting heart rate or blood pressure. This makes it a valuable add-on therapy for patients with persistent angina despite beta-blocker or calcium channel blocker therapy, and particularly useful for those who cannot tolerate the hemodynamic effects of traditional anti-anginal agents. The MERLIN-TIMI 36 trial demonstrated that ranolazine reduced recurrent ischemia but did not confer a mortality benefit. The drug is dosed at 500 mg twice daily, with the option to increase to 1000 mg twice daily, and clinicians must be aware of its potential for QT prolongation, avoiding concomitant use with other QT-prolonging medications.

Antiplatelet Therapy

Antiplatelet therapy forms the foundation of secondary prevention in stable ischemic heart disease. Low-dose aspirin at 75 to 100 mg daily reduces the composite of myocardial infarction, stroke, and cardiovascular death by approximately 25%. For patients who are aspirin-intolerant, clopidogrel at 75 mg daily represents the alternative, as established in the CAPRIE trial. The concept of dual pathway inhibition has been advanced by the COMPASS trial, which demonstrated that the combination of low-dose rivaroxaban at 2.5 mg twice daily plus aspirin reduced major adverse cardiovascular events by 24% compared to aspirin alone, albeit with an increase in major bleeding. The net clinical benefit of this approach favors its use in patients with high ischemic risk, such as those with polyvascular disease, multivessel coronary artery disease, chronic kidney disease, heart failure, or diabetes. Dual antiplatelet therapy in the setting of stable coronary artery disease is not routinely recommended unless the patient has undergone recent stent implantation or an acute coronary syndrome.

ISCHEMIA Trial and Revascularization Strategy

ISCHEMIA Trial Key Findings

The ISCHEMIA trial represents the most important contemporary study shaping the management of stable ischemic heart disease. This trial randomized 5,179 patients with moderate-to-severe ischemia on stress testing and stable coronary artery disease to either an initial invasive strategy with catheterization and revascularization or a conservative strategy with guideline-directed medical therapy alone, reserving catheterization only for treatment failure. At a median follow-up of 3.2 years, there was no difference in the primary composite endpoint of cardiovascular death, myocardial infarction, hospitalization for unstable angina, heart failure, or resuscitated cardiac arrest.

The nuances of the trial findings are clinically important. The invasive strategy provided superior angina relief, with significant improvements in Seattle Angina Questionnaire scores at 3 months that were sustained over time. However, the invasive arm experienced more procedural myocardial infarction from periprocedural biomarker elevation, while the conservative arm had more spontaneous myocardial infarction, reflecting higher rates of type 1 myocardial infarction over time. Critical exclusion criteria must be recognized when applying these results: patients with left main stenosis of 50% or more were excluded by coronary CT angiography before randomization, as were those with an ejection fraction below 35%, recent acute coronary syndrome, NYHA Class III-IV heart failure, and unacceptable angina on optimal medical therapy. The companion ISCHEMIA-CKD trial, conducted in patients with an estimated glomerular filtration rate below 30, found no benefit from the invasive strategy and a trend toward harm.

Current Approach to Revascularization in SIHD

The current approach to revascularization in stable ischemic heart disease recognizes two principal indications. The most common indication is symptom relief in patients with angina refractory to optimal medical therapy. Prognostic indications, where revascularization may improve survival, include left main disease with 50% or greater stenosis, proximal left anterior descending artery disease with 70% or greater stenosis, three-vessel disease particularly when the ejection fraction is below 50%, and a large ischemic burden involving more than 10% of the left ventricle, although the ISCHEMIA trial challenges the prognostic benefit in many of these scenarios. The STICH trial demonstrated that in patients with an ejection fraction below 35% and viable myocardium, coronary artery bypass grafting plus optimal medical therapy provided a long-term 10-year mortality benefit compared to optimal medical therapy alone. For complex coronary artery disease involving the left main, multivessel disease, or diabetes, a heart team approach with multidisciplinary discussion is essential.

Invasive Assessment of Stenosis Severity

Fractional Flow Reserve (FFR)

Fractional flow reserve provides a physiologic assessment of coronary stenosis severity by measuring the ratio of distal coronary pressure to aortic pressure during maximal hyperemia induced by adenosine or regadenoson. An FFR value of 0.80 or below indicates a hemodynamically significant stenosis for which revascularization is recommended, while a value above 0.80 indicates a non-flow-limiting lesion that can be safely deferred with continued medical therapy. The FAME trial demonstrated that FFR-guided percutaneous coronary intervention reduced the composite of death, myocardial infarction, and repeat revascularization compared to angiography-guided intervention. The subsequent FAME 2 trial showed that FFR-guided PCI plus optimal medical therapy reduced urgent revascularization compared to optimal medical therapy alone, though no mortality difference was observed.

Instantaneous Wave-Free Ratio (iFR)

The instantaneous wave-free ratio provides an alternative resting physiologic index measured during the diastolic wave-free period, eliminating the need for adenosine administration. A threshold of 0.89 or below defines a significant lesion, while values above 0.89 indicate a non-significant lesion. The DEFINE-FLAIR and iFR-SWEDEHEART trials established that iFR is non-inferior to FFR for guiding clinical outcomes. A practical hybrid approach uses iFR as the initial assessment, proceeding to FFR for confirmation when the iFR falls in the borderline range of 0.86 to 0.93.

Intravascular Imaging

Intravascular imaging complements physiologic assessment by providing detailed anatomic characterization of coronary lesions and optimizing percutaneous intervention. Intravascular ultrasound uses ultrasound technology to assess plaque burden, vessel remodeling, and lumen area, with a minimum lumen area below 6.0 mm squared in the left main or below 4.0 mm squared in non-left main arteries suggesting hemodynamic significance. Optical coherence tomography offers 10-fold higher resolution than intravascular ultrasound, enabling detection of thin-cap fibroatheroma, plaque erosion, thrombus, and stent malapposition, though it is limited by the need for blood clearance and shallow tissue penetration. Multiple contemporary trials including ILUMIEN IV, OCTOBER, and RENOVATE-COMPLEX PCI have demonstrated that intravascular imaging-guided percutaneous coronary intervention yields superior outcomes compared to angiography-guided intervention alone.

<image> An illustration showing invasive physiologic assessment of coronary stenosis. The main image shows a coronary angiogram with a 70% stenosis in the mid-LAD artery. A pressure wire is positioned distal to the stenosis. Two pressure tracings are overlaid: (1) Aortic pressure (Pa, in red) measured from the guide catheter, showing normal waveform ~100/60 mmHg. (2) Distal coronary pressure (Pd, in blue) measured from the pressure wire tip, showing attenuated waveform ~75/55 mmHg during maximal hyperemia. FFR calculation shown: FFR = mean Pd/mean Pa = 72/95 = 0.76 (significant, indicating hemodynamic limitation). Below: a second scenario showing the same anatomy but with iFR measurement at rest during the diastolic wave-free period. The diastolic window is highlighted in green on the pressure tracing, with iFR calculation: mean Pd(WFP)/mean Pa(WFP) = 0.87 (significant, <0.89). Include a decision box: "FFR <= 0.80 or iFR <= 0.89 → Revascularize. FFR > 0.80 or iFR > 0.89 → Medical therapy." Use clear waveform graphics with labeled axes. </image>

Coronary Microvascular Disease

Diagnosis

Coronary microvascular disease accounts for a substantial proportion of patients presenting with angina and non-obstructive coronary arteries, a condition referred to as ANOCA or INOCA, and is found in 30 to 50% of patients undergoing catheterization for angina evaluation. Comprehensive invasive assessment through coronary function testing in the catheterization laboratory has become the diagnostic standard. Acetylcholine provocation testing evaluates for epicardial vasospasm, defined as greater than 90% diameter reduction with concurrent chest pain and electrocardiographic changes, as well as microvascular spasm, identified when chest pain and electrocardiographic changes occur without epicardial spasm. Adenosine administration enables measurement of coronary flow reserve, with a value below 2.0 to 2.5 indicating coronary microvascular dysfunction, and the index of microvascular resistance, with a value above 25 confirming microvascular disease. Non-invasive evaluation includes positron emission tomography with quantitative coronary flow reserve assessment and stress cardiac magnetic resonance imaging with perfusion analysis.

Treatment

Treatment of coronary microvascular disease is tailored to the specific endotype identified on invasive testing. For patients with coronary microvascular dysfunction without vasospasm, first-line therapies include beta-blockers, angiotensin-converting enzyme inhibitors or angiotensin receptor blockers, statins, and ranolazine, complemented by comprehensive lifestyle modification. Epicardial vasospasm is managed with calcium channel blockers as first-line therapy and long-acting nitrates, with the important caveat that beta-blockers should be avoided in this population because they may worsen vasospasm through unopposed alpha-adrenergic activity. Microvascular spasm is treated with calcium channel blockers, nitrates, and ranolazine. Risk factor optimization targeting hypertension, diabetes, smoking, and dyslipidemia is paramount across all endotypes. The CorMicA trial demonstrated that stratified medical therapy based on invasive coronary function testing improved angina outcomes compared to standard care, providing strong evidence in support of systematic invasive evaluation of patients with INOCA and ANOCA.

Key Clinical Pearls

• The ISCHEMIA trial demonstrated that routine invasive strategy does not reduce CV death or MI compared to conservative management in stable CAD with moderate-severe ischemia -- medical therapy is the foundation; revascularization is for symptom relief or true refractory angina
• Always exclude left main disease with CCTA before deferring catheterization -- left main >= 50% was excluded from ISCHEMIA and remains a Class I indication for revascularization
• FFR/iFR-guided PCI is superior to angiography-guided PCI -- never base revascularization decisions on visual angiographic assessment alone for intermediate lesions (40-70%)
• Coronary microvascular disease is underdiagnosed and undertreated; ANOCA/INOCA patients are not "normal" and deserve systematic evaluation with invasive coronary function testing; treatment tailored to endotype improves outcomes (CorMicA)
• Nitrate tolerance develops rapidly with continuous use -- always prescribe long-acting nitrates with an asymmetric dosing schedule (12-14 hours on, 10-12 hours off)
• Dual pathway inhibition (rivaroxaban 2.5 mg BID + aspirin) should be considered in patients with polyvascular disease, diabetes, or other high-risk features -- COMPASS demonstrated a significant reduction in MACE with acceptable bleeding trade-off

References

• Knuuti J, et al. 2019 ESC Guidelines for the Diagnosis and Management of Chronic Coronary Syndromes. Eur Heart J. 2020;41:407-477.
• Maron DJ, et al. Initial Invasive or Conservative Strategy for Stable Coronary Disease (ISCHEMIA). NEJM. 2020;382:1395-1407.
• De Bruyne B, et al. Fractional Flow Reserve-Guided PCI versus Medical Therapy in Stable Coronary Disease (FAME 2). NEJM. 2012;367:991-1001.
• Eikelboom JW, et al. Rivaroxaban with or without Aspirin in Stable Cardiovascular Disease (COMPASS). NEJM. 2017;377:1319-1330.
• Ford TJ, et al. Stratified Medical Therapy Using Invasive Coronary Function Testing in Angina (CorMicA). JACC. 2018;72:2841-2855.

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