Should I continue the Isoket (isosorbide dinitrate) drip in a 70-year-old female patient with hypertension, unstable angina, and sinus bradycardia, who has a current heart rate of 52 beats per minute and improved chest pain from 6/10 to 1-2/10, with troponin levels less than 50 ng/L?

Management of Isoket (Isosorbide Dinitrate) Drip in Unstable Angina with Bradycardia

You should discontinue or significantly reduce the Isoket drip given the heart rate of 52 bpm and marked clinical improvement in chest pain from 6/10 to 1-2/10. 1, 2

Rationale for Discontinuation

Bradycardia as a Critical Contraindication

• Sinus bradycardia <45 bpm is an absolute contraindication to stress testing with vasodilators, and a heart rate of 52 bpm approaches this threshold, particularly in the context of ongoing nitrate therapy that can further reduce heart rate 3
• The FDA drug label for isosorbide dinitrate warns that nitrate therapy can cause lightheadedness and hemodynamic instability, which is particularly concerning in patients with borderline bradycardia 2
• Complete atrioventricular block and ventricular asystole have been documented following isosorbide dinitrate administration, especially in elderly patients with pre-existing conduction abnormalities 4

Clinical Improvement Supports De-escalation

• Your patient has achieved excellent symptomatic relief (chest pain reduced from 6/10 to 1-2/10), which indicates that the acute ischemic episode is resolving 1
• Serial troponin levels remain <50 ng/L, which is below the 99th percentile cutoff for myocardial necrosis, suggesting this may represent unstable angina rather than NSTEMI 1, 5
• The American College of Cardiology guidelines recommend that anti-ischemic therapy should be titrated to symptom control, and continuing aggressive vasodilator therapy in a patient with minimal residual symptoms and bradycardia poses unnecessary risk 3, 1

Recommended Management Algorithm

Immediate Actions

• Discontinue or reduce the Isoket drip to the minimum effective dose while monitoring for recurrent chest pain 1, 2
• Initiate continuous cardiac monitoring with particular attention to heart rate, blood pressure, and rhythm abnormalities 3, 1
• Avoid beta-blockers given the current bradycardia, as they would further reduce heart rate and could precipitate complete heart block 3

Alternative Anti-Ischemic Strategies

• Consider transitioning to oral long-acting nitrates once the patient is stable and pain-free for 24 hours, as this allows for a nitrate-free interval to prevent tolerance 3, 2
• Calcium channel blockers (such as diltiazem or amlodipine) may be considered as alternative anti-ischemic agents, though rate-limiting calcium channel blockers should be used cautiously given the bradycardia 3, 6
• Ensure the patient is on appropriate antiplatelet therapy (aspirin and clopidogrel) and anticoagulation as per unstable angina protocols 1, 7

Awaiting Echocardiography Results

• The echocardiogram is critical to assess for left ventricular function, regional wall motion abnormalities, and to rule out Takotsubo cardiomyopathy, which can mimic unstable angina in elderly women 3
• If the echo reveals significant left ventricular dysfunction or high-risk features, an early invasive strategy with coronary angiography within 24 hours should be pursued 1, 7

Critical Pitfalls to Avoid

Nitrate Tolerance and Rebound

• Continuous nitrate infusion for >24 hours leads to tolerance, reducing anti-anginal efficacy 3, 2
• Abrupt discontinuation of nitrates after prolonged use can cause rebound angina and increased ischemic events, so taper gradually if the patient has been on the drip for >24 hours 2

Hemodynamic Instability

• Nitrates can cause profound hypotension, particularly in elderly hypertensive patients, and this risk is amplified by bradycardia which limits compensatory heart rate increase 2, 4
• Monitor blood pressure closely during any adjustment of the Isoket drip, as systolic blood pressure <90 mmHg is a contraindication to continued vasodilator therapy 3

Misdiagnosis Risk

• Unstable angina with negative troponin still carries significant cardiovascular risk (adjusted hazard ratio 2.97 for major cardiovascular events), so do not be falsely reassured by the negative troponin alone 5
• Ensure other life-threatening causes of chest pain (pulmonary embolism, aortic dissection) have been adequately excluded before attributing symptoms solely to cardiac ischemia 3

Next Steps in Management

• Plan for coronary angiography if the patient has recurrent ischemia, positive stress testing, or high-risk features on echocardiography 1, 7
• Initiate high-intensity statin therapy and ACE inhibitor if hypertension or left ventricular dysfunction is present 7
• Maintain the patient in a monitored setting for at least 24 hours after pain resolution to observe for recurrent ischemia or arrhythmias 3