Refractory Angina: Options When Standard Therapy Fails

Definition and Pathophysiology

Refractory angina is a chronic syndrome of persistent ischaemic symptoms despite the exhaustion of conventional therapeutic options. It is defined by symptoms lasting more than 3 months and attributable to established reversible myocardial ischaemia in either of two settings:

• Obstructive coronary artery disease (CAD) that cannot be controlled despite escalation of antianginal medical therapy, coronary artery bypass grafting (CABG), or percutaneous coronary intervention (PCI), including attempted recanalization of a chronic total coronary occlusion.

• Angina or ischaemia with non-obstructive coronary arteries (ANOCA/INOCA), after appropriate investigation has identified the relevant endotype and its treatment options have been addressed.

ANOCA/INOCA should not be labelled refractory before further diagnostic evaluation. The underlying endotype must first be defined, because management depends on the mechanism responsible for symptoms and ischaemia.

The increasing prevalence of refractory angina reflects population ageing and improved survival among patients with CAD following advances in anti-ischaemic treatment and coronary revascularization. Consequently, more patients survive with severe, diffuse CAD that is no longer amenable to additional mechanical revascularization. Despite treatment with antianginal drugs and PCI or CABG, daily or weekly angina remains present in approximately 2%–24% of patients with CAD.

The pathophysiology of refractory angina is heterogeneous. In obstructive CAD, symptoms may result from extensive or diffuse epicardial disease, chronic total occlusion, incomplete revascularization, or coronary anatomy unsuitable for further intervention. In ANOCA/INOCA, coronary atherosclerosis, endothelial dysfunction, and distinct coronary functional abnormalities may produce ischaemia without an obstructive epicardial lesion.

Once conventional anti-ischaemic targets have been exhausted, proposed therapeutic approaches act through several broad mechanisms:

• Promotion of coronary collateral growth.

• Redistribution of myocardial blood flow across the ventricular wall.

• Modification of coronary venous haemodynamics.

• Neuromodulation of cardiac pain signalling.

• Experimental angiogenic or regenerative strategies.

The syndrome is clinically important not only because of persistent symptoms, but also because quality of life is often poor, hospitalizations are frequent, and healthcare-resource utilization is high.

Clinical Presentation and Symptoms

The dominant manifestation is chronic, recurrent angina or an anginal equivalent caused by reversible ischaemia. Symptoms may remain present daily or weekly despite multiple antianginal agents and prior revascularization procedures. In many patients, the burden is sufficiently severe to limit ordinary activities and substantially impair quality of life.

The clinical impact should be assessed in terms of:

• Symptom frequency and duration.

• Functional limitation and effect on activities of daily living.

• Workload or exertion required to provoke symptoms.

• Response to current antianginal therapy.

• Adverse effects that restrict further drug escalation.

• Previous PCI, CABG, or attempted chronic total-occlusion recanalization.

• Patient preferences concerning additional medication, invasive investigation, and device-based treatment.

Refractory angina should be distinguished from symptoms caused or amplified by potentially reversible precipitating conditions. Evaluation should seek factors that increase myocardial oxygen demand or worsen ischaemia, including anaemia, uncontrolled hypertension, thyrotoxicosis, tachyarrhythmias, uncontrolled heart failure, and concomitant valvular heart disease.

In patients with ANOCA/INOCA, symptoms may persist despite non-obstructive coronary anatomy. Such patients require a mechanism-based assessment rather than reassurance based solely on the absence of obstructive CAD.

Evaluation and Physical Examination

Clinical assessment

The assessment begins with confirmation that symptoms are attributable to reversible myocardial ischaemia and that conventional options have genuinely been optimized. This requires review of:

• The duration and pattern of symptoms.

• The presence and extent of obstructive CAD.

• Previous revascularization procedures and their completeness.

• Current antianginal therapy, adherence, tolerability, and opportunities for further escalation.

• Whether a chronic total occlusion has been considered for recanalization.

• Potential precipitating or aggravating conditions.

• The degree of functional limitation and quality-of-life impairment.

• Patient goals and preferences.

Management should be patient-centred and multidisciplinary. Shared decision-making is particularly important because revascularization and device-based therapies are generally directed at symptom relief and improvement in health status, whereas their effects on mortality and myocardial infarction may be limited or uncertain in stable ischaemic disease.

Physical examination

The source material does not provide a detailed physical-examination protocol specific to refractory angina. Examination should nevertheless be directed toward identifying conditions that may intensify angina or influence treatment decisions, particularly heart failure, hypertension, valvular disease, tachyarrhythmia, and clinical evidence of anaemia or thyroid disease.

Diagnostics

Coronary anatomy and revascularization assessment

Coronary angiography is indicated when symptoms remain refractory after titration of antianginal therapy and revascularization is being considered. The purpose is to define coronary anatomy and determine whether further PCI or CABG is feasible.

The decision to pursue additional revascularization should incorporate:

• The complexity and diffuseness of CAD.

• The likelihood of technical success with PCI.

• The possibility of complete revascularization.

• The volume of myocardium supplied by the target vessel.

• The severity and distribution of ischaemia.

• Lesion-specific factors such as small vessel diameter, long lesions, total occlusion, and saphenous vein-graft disease.

• The anticipated risks of restenosis or acute procedural failure.

• The patient’s symptoms, functional impairment, comorbidities, and preferences.

When anatomy is complex or comorbidity burden is high, a multidisciplinary heart-team assessment is appropriate. The team should include non-interventional cardiology, interventional cardiology, and cardiac surgery expertise.

Functional assessment in ANOCA/INOCA

For patients with poor quality of life, documented or suspected ANOCA/INOCA, invasive coronary functional testing is recommended to define the relevant endotype and guide treatment. This is a Class I, Level B recommendation in the cited guideline material.

Invasive functional assessment is particularly important before diagnosing refractory angina in a patient with non-obstructive coronary arteries. It permits a distinction between different mechanisms of ANOCA/INOCA and supports individualized therapy.

Non-invasive assessment

The source material describes non-invasive risk stratification for stable ischaemic disease, including stress perfusion imaging, stress echocardiography, exercise testing, and assessment of left ventricular ejection fraction. These tests may identify extensive ischaemia or ventricular dysfunction relevant to revascularization decisions.

High-risk features listed in the source material include:

• Resting left ventricular ejection fraction below 35%.

• Exercise-induced left ventricular ejection fraction below 35%.

• A high-risk treadmill score of −11 or less.

• A large stress-induced perfusion defect, particularly in the anterior territory.

• Multiple moderate-sized stress-induced perfusion defects.

• A large fixed perfusion defect with left ventricular dilatation or increased lung uptake.

• A moderate stress-induced perfusion defect accompanied by left ventricular dilatation or increased lung uptake.

• Stress echocardiographic evidence of extensive ischaemia.

• Wall-motion abnormalities involving more than two segments during low-dose dobutamine stress or at a low heart rate.

These findings may influence the assessment of myocardial jeopardy and the potential role of revascularization, but the source material emphasizes that the prognostic value of routine invasive management in stable disease with moderate or severe inducible ischaemia is complex.

Electrocardiography and electrophysiology

The source material does not provide specific electrocardiographic findings diagnostic of refractory angina. Electrophysiological testing is not described as a routine diagnostic component of refractory angina evaluation. Neuromodulatory treatment, particularly spinal cord stimulation, is discussed as a therapeutic option rather than as an electrophysiological diagnostic procedure.

Biomarkers and Laboratory Findings

No biomarker or laboratory profile specific to refractory angina is provided in the source material.

Laboratory and clinical assessment should nevertheless address potentially reversible precipitants and treatment-limiting comorbidities. The cited management framework specifically identifies anaemia and thyrotoxicosis as conditions that may aggravate angina. Renal function and other comorbidities are relevant when considering intensive medical therapy, angiography, PCI, or CABG, although no refractory-angina-specific laboratory thresholds are provided.

Treatment and Management

General principles

Management has two simultaneous objectives:

• To use disease-modifying treatment to prolong life and reduce major cardiovascular events, including myocardial infarction, acute coronary syndrome hospitalization, and heart failure.

• To improve health status, quality of life, and functional capacity so that angina or ischaemia does not adversely affect daily activities.

Refractory angina should be approached only after:

• Reversible aggravating conditions have been identified and treated.

• Lifestyle and cardiovascular risk-factor management have been addressed.

• Antianginal therapy has been optimized and escalated as tolerated.

• Coronary anatomy has been defined where further revascularization may be feasible.

• PCI or CABG options, including chronic total-occlusion recanalization where appropriate, have been considered.

Lifestyle and risk-factor management

All patients with stable ischaemic disease should receive lifestyle and risk-factor management. The cited integrated approach includes:

• Physical exercise and lifestyle counselling.

• Dietary management.

• High-intensity statin therapy.

• Low-dose aspirin, or clopidogrel as an alternative.

• Treatment of hypertension, diabetes, and other comorbidities.

• Identification and correction of factors that intensify angina.

For ANOCA/INOCA, tailored counselling concerning lifestyle factors is specifically recommended because coronary atherosclerosis and endothelial dysfunction may be present even without obstructive epicardial disease.

Antianginal pharmacotherapy

The source material describes a stepwise pharmacological strategy for stable angina:

• Begin with a beta blocker or calcium antagonist for most patients.

• Use sublingual nitroglycerin for acute relief and, when required, prophylaxis.

• If angina persists, add a second agent, selected from a calcium antagonist, beta blocker, or long-acting nitrate.

• Long-acting nitrates should be administered using schedules designed to avoid nitrate tolerance.

• If symptoms continue despite two antianginal agents, add a third agent, with selection guided by adverse effects, blood pressure, heart rate, conduction disease, tachyarrhythmias, left ventricular dysfunction, and patient preference.

• Ranolazine is an alternative or additional agent when low heart rate or blood pressure limits initiation or titration of other drugs.

The source material does not provide specific doses for these antianginal agents. It also does not provide a refractory-angina-specific drug regimen beyond the treatment sequence above.

Drug selection should account for concomitant disease. For example, hypertension, left ventricular dysfunction, and heart-failure symptoms may influence whether a beta blocker, calcium antagonist, or long-acting nitrate is selected. Further escalation must be balanced against hypotension, bradycardia, conduction-system disease, and other treatment-related adverse effects.

Revascularization

Revascularization remains an important part of an overall management strategy, but it should not be considered a substitute for guideline-directed medical therapy and lifestyle management.

For most patients with stable ischaemic disease, initial medical treatment is generally preferred. Revascularization is principally reserved for:

• Persistent lifestyle-limiting symptoms despite optimized medical therapy.

• Patients with left ventricular dysfunction.

• Selected patients with high-risk anatomical or clinical features.

• Patients who prefer revascularization for symptom relief after a shared decision-making discussion.

In stable disease, revascularization has not generally been shown to reduce death or myocardial infarction compared with medical therapy, except in selected anatomical settings in which CABG may provide prognostic benefit. Contemporary trial data summarized in the source material indicate that routine initial invasive treatment in patients with moderate or severe inducible ischaemia did not reduce the primary composite of death, myocardial infarction, unstable angina, heart failure, or resuscitated cardiac arrest at five years, although invasive treatment improved angina-related health status and reduced spontaneous myocardial infarction at the cost of more procedural myocardial infarction.

Accordingly, the potential benefits of revascularization should be framed primarily in terms of symptom relief and quality of life unless the patient has an anatomical or ventricular-function profile associated with a separate prognostic indication.

Enhanced external counterpulsation

Enhanced external counterpulsation (EECP) is a non-invasive treatment generally considered after multiple antianginal agents and revascularization options have failed.

A typical course consists of 35 one-hour treatments delivered over approximately seven weeks. Observational data suggest reductions in angina frequency, improved exercise tolerance, and better quality of life, with responses reported to persist for up to two years. In a randomized, double-blind, sham-controlled study, active counterpulsation increased exercise time to ST-segment depression, reduced angina, and improved health-related quality of life for at least one year.

Important limitations remain:

• Much of the favourable evidence comes from uncontrolled studies.

• Sham-controlled evidence is limited.

• Definitive reduction in the extent of ischaemia on perfusion imaging has not been demonstrated.

• The mechanisms underlying benefit remain incompletely understood.

EECP is therefore a practical option for selected patients with persistent symptoms after standard therapy, but the evidence base does not establish a clear effect on hard clinical outcomes.

Coronary sinus reducer

The coronary sinus reducer is an implanted stainless-steel device that produces controlled narrowing of the coronary sinus. The intended physiological effect is to increase coronary sinus pressure and improve perfusion in the left anterior descending coronary artery territory.

It is considered after medical therapy and mechanical revascularization options have been exhausted. The device may be considered in experienced centres for patients with debilitating angina and obstructive CAD despite optimal medical and revascularization treatment. This is a Class IIb, Level B recommendation in the cited guideline material.

In a meta-analysis of eight registries and one randomized trial including 846 patients with refractory angina:

• 76% improved by at least one Canadian Cardiovascular Society angina class.

• 40% improved by at least two Canadian Cardiovascular Society angina classes.

A small proof-of-concept randomized trial found no evidence that the device improved transmural myocardial perfusion, but it was associated with improved angina symptoms compared with placebo.

The main clinical role of the device is therefore symptom improvement rather than an established reduction in myocardial ischaemia or cardiovascular events.

Spinal cord stimulation

Spinal cord stimulation is a neuromodulatory option for patients with refractory angina who are not candidates for further coronary revascularization. A specially designed electrode is inserted into the epidural space.

Its proposed analgesic mechanism is based on modulation of spinal pathways: stimulation of non-pain-transmitting axons is intended to reduce transmission from pain-transmitting axons to the brain. Observational studies have reported reductions in angina frequency and severity in up to 80% of patients, while small randomized studies, including a sham-controlled study, have suggested improvement in symptoms and functional status.

An apparent anti-ischaemic effect has also been reported, although the mechanism is not readily explained. The technique should be reserved for patients in whom other treatment options have been exhausted.

Investigational therapies

Several experimental approaches are under evaluation:

• Angiogenic treatment using vascular endothelial growth factors.

• Fibroblast growth factors.

• Intramyocardial delivery of CD34+ stem cells.

These approaches remain investigational. Further randomized controlled trials are required to establish feasibility, efficacy, safety, and the patient subgroups most likely to benefit.

Guideline Recommendations

The cited recommendations can be summarized as follows:

The wider guideline framework supports the following principles:

• Begin with lifestyle management, risk-factor modification, and guideline-directed medical therapy.

• Use shared decision-making when choosing between further medication and revascularization.

• Reserve non-pharmacological therapies such as EECP and spinal cord stimulation for patients with refractory ischaemic symptoms after medical therapy and revascularization have failed.

• Consider a multidisciplinary heart-team approach when coronary anatomy is complex or comorbidity burden is substantial.

• Treat ANOCA/INOCA according to the defined coronary functional endotype rather than assuming that non-obstructive anatomy excludes clinically important ischaemia.

Prognosis and Follow-Up

Refractory angina is associated with poor quality of life, frequent hospitalization, and substantial healthcare-resource utilization. Its clinical course is chronic, and treatment often aims to reduce symptoms and improve function rather than achieve complete elimination of ischaemia.

The prognosis depends on the underlying substrate, including:

• Extent and complexity of CAD.

• Left ventricular function.

• The amount of jeopardized viable myocardium.

• Severity and distribution of inducible ischaemia.

• Presence of ANOCA/INOCA and its specific endotype.

• Comorbid conditions and their control.

• Feasibility of complete revascularization.

• Response to antianginal and non-pharmacological therapy.

Follow-up should reassess symptom burden, functional capacity, quality of life, hospitalizations, medication tolerability, and the emergence of new clinical features suggesting acute coronary syndrome or heart failure. Reversible aggravating factors should be revisited, and antianginal therapy should be adjusted according to heart rate, blood pressure, conduction status, ventricular function, and patient preference.

Patients treated with EECP, spinal cord stimulation, or a coronary sinus reducer require assessment of symptomatic response and functional status. The available evidence for these interventions is limited by small patient numbers and relatively short follow-up. Larger sham-controlled randomized trials are needed to determine their long-term clinical role and to identify which aetiological subgroups benefit most.

Future management is likely to depend on better stratification by mechanism and endotype, followed by individualized escalation through medical, revascularization, device-based, and neuromodulatory therapies.