Should a patient with a history of coronary artery disease, hypertension, or other cardiac conditions continue taking Imdur (isosorbide mononitrate) as prescribed before undergoing a heart catheterization procedure?

Should Imdur Be Given Before Heart Catheterization?

Continue Imdur (isosorbide mononitrate) on the morning of heart catheterization unless the patient is hemodynamically unstable or hypotensive. There are no guideline recommendations to withhold nitrates before diagnostic cardiac catheterization, and abrupt discontinuation may worsen anginal symptoms 1, 2.

Rationale for Continuation

Antianginal Protection

• Imdur is indicated for prevention of angina pectoris due to coronary artery disease and provides effective prophylaxis for up to 12 hours after administration 1, 3.
• The drug maintains antianginal efficacy during repeated administration without evidence of classical tolerance at standard doses 3.
• Patients undergoing heart catheterization remain at risk for myocardial ischemia during the procedure, particularly if significant coronary disease is present 4.

Risks of Abrupt Withdrawal

• Abrupt discontinuation of long-term isosorbide mononitrate therapy may exacerbate anginal symptoms 1, 3.
• In one study, 3 out of 32 patients (9%) required hospitalization due to sudden deterioration of symptoms when isosorbide mononitrate was abruptly withdrawn 2.
• Industrial workers with chronic nitrate exposure have experienced chest pain, acute myocardial infarction, and sudden death during temporary nitrate withdrawal, demonstrating true physical dependence 1.

Critical Safety Considerations

When to Withhold Imdur

Hold the morning dose if any of the following are present:

• Hemodynamic instability or hypotension (systolic BP <90 mmHg) 1.
• Volume depletion or clinical signs of hypovolemia 1.
• Planned transseptal puncture or left ventricular puncture requiring complete reversal of anticoagulation (though this relates more to anticoagulant management than nitrate therapy) 4.

Hypotension Risk Management

• Severe hypotension, particularly with upright posture, may occur with even small doses of isosorbide mononitrate 1.
• Hypotension induced by the drug may be accompanied by paradoxical bradycardia and increased angina pectoris 1.
• The vasodilating effects may be additive with other vasodilators used during catheterization, requiring careful blood pressure monitoring 1.

Procedural Considerations

Catheterization Guidelines

• The 2011 ACC/AHA/SCAI PCI guidelines extensively address antiplatelet and anticoagulant management but do not recommend withholding chronic antianginal medications like nitrates 4.
• Cardiac catheterization guidelines focus on procedural anticoagulation and antiplatelet therapy rather than chronic oral antianginal agents 4, 5.

Medication Timing

• If the patient takes Imdur once daily in the morning (standard dosing), give it as scheduled on the morning of the procedure unless contraindicated 1, 3.
• The onset of action is not sufficiently rapid to abort acute anginal episodes, so it functions as prophylaxis rather than acute treatment 1.

Common Pitfalls to Avoid

• Do not confuse nitrate management with antiplatelet/anticoagulant management: Guidelines extensively address when to hold clopidogrel, prasugrel, or anticoagulants before procedures, but these do not apply to chronic nitrate therapy 4.
• Do not assume all cardiac medications should be held: Unlike some antihypertensives (e.g., ACE inhibitors/ARBs which may be held in select cases), nitrates serve a protective antianginal function during procedures 6.
• Monitor for additive hypotensive effects: Be prepared to manage hypotension if it occurs, particularly when combined with procedural sedation or other vasodilators 1.
• Ensure adequate hydration: Volume depletion significantly increases hypotension risk with nitrates 1.