Stress Testing Protocols

Cardiac stress testing allows the assessment of coronary flow reserve by comparing myocardial perfusion at rest versus localized stress conditions.

Learning Objectives

• Compare and contrast exercise vs. pharmacologic stress
• Describe the mechanism of action of adenosine, regadenoson, and dobutamine
• Identify contraindications for each stress modality
• Recognize signs of ischemia during stress testing

Exercise Stress Testing

The preferred physiological method if the patient can achieve adequate workload (>85% MPHR).

• Method: Bruce Protocol (standard) or Modified Bruce
• Target: >85% of Maximum Predicted Heart Rate (220 - Age)
• Radiotracer Injection: At peak stress; exercise continues for ~1 min after injection.
• Advantages: Assesses functional capacity, symptom reproduction, ECG changes.
• Contraindications: Unstable angina, severe aortic stenosis, uncontrolled arrhythmia.

Pharmacologic Stress Agents

Used when patients cannot exercise adequately (LBBB, orthopedic issues, poor functional capacity).

Vasodilators

Agents: Adenosine, Regadenoson (Lexiscan), Dipyridamole

• Mechanism: Bind to A2A receptors → coronary vasodilation (hyperemia).
• Flow increase: 3-5x baseline flow.
• Contraindications:
  • Severe reactive airway disease (asthma/COPD with wheezing)
  • 2nd/3rd degree AV block (without pacemaker)
  • Hypotension (SBP < 90 mmHg)
  • Caffeine intake < 12h (competes with receptors)
• Reversal Agent: Aminophylline (50-100 mg IV)

Dobutamine

• Mechanism: Beta-1 agonist → increases heart rate and contractility (increases oxygen demand).
• Indication: Used when vasodilators are contraindicated (e.g., severe asthma).
• Target: >85% MPHR (Atropine often added if target not reached).
• Contraindications: Tachyarrhythmias, severe hypertension.

Protocol Selection Algorithm

1. Can patient exercise?
   • Yes, able to walk briskly? → Exercise Stress (Bruce)
   • No:
     • History of Asthma/Wheezing?
       • Yes → Dobutamine
       • No → Regadenoson/Adenosine