13.3 Exercise and Pharmacologic Stress Testing

13.3 Exercise and Pharmacologic Stress Testing

Quick Answer: Exercise (Bruce / modified Bruce / bike) is preferred when the patient can walk and the ECG is interpretable. Vasodilators (adenosine, dipyridamole, regadenoson) create coronary hyperemia when exercise is inadequate; dobutamine raises demand when vasodilators are contraindicated. Know leads, stop criteria, RP injection timing, side effects, and aminophylline reversal. Caffeine ruins vasodilator stress.

Stress testing is a team process. CNMT items still expect you to set up, monitor, inject on time, and recognize danger.

Basic ECG for the Nuclear Technologist

Conduction path: SA node → atria (P) → AV node/His–Purkinje → ventricles (QRS) → repolarization (T). Watch PR (AV conduction), QRS width (bundle branch/ventricular beats), and ST segment (ischemia zone during stress).

You are not the final ECG reader, but you must not ignore alarms, severe pain with ST change, or collapse.

Lead Placement

Standard 12-lead monitoring:

Prep skin (shave/abrade as needed); fix loose electrodes—motion noise mimics arrhythmia. Baseline LBBB, paced rhythm, digoxin effect, or LVH with strain limits ECG ischemia diagnosis (favor imaging endpoints).

Exercise Protocols

Bruce treadmill: 3-minute stages increasing speed and grade (classically starts 1.7 mph / 10%). Goal often ≥85% maximum predicted HR (rough rule 220 − age) unless symptoms force earlier stop. Inject MPI tracer at peak and continue exercise ~1 minute when safe.

Modified Bruce: gentler early stages for deconditioned or limited patients before standard workloads.

Bicycle ergometry: watt-stepped upright or supine bike when gait is limited or bike imaging geometry is preferred. Same HR, BP, and symptom rules apply.

Contraindications and Termination

Absolute contraindications (teaching—follow lab policy): acute MI (early), high-risk unstable angina, uncontrolled symptomatic arrhythmia, severe symptomatic AS, decompensated HF, acute PE/dissection/myocarditis-pericarditis, inability to cooperate safely.

Relative: left main disease, moderate stenotic valve disease, severe rest HTN, electrolyte extremes, HOCM with obstruction, high-grade AV block—clinician call.

Patient request to stop is honored for safety; convert to pharmacologic imaging if the study must finish.

Always record baseline BP/HR, stage-by-stage values, peak rate-pressure product when used, total exercise time, reason for stopping, and exact tracer injection clock time relative to peak stress or drug administration.

Pharmacologic Stress

Use when exercise is inadequate, when LBBB/paced rhythm makes exercise MPI artifact-prone (prefer vasodilator), or when ordered.

Vasodilators

Vasodilator cautions: active wheezing / severe asthma or bronchospasm, high-grade AV block without pacemaker, profound hypotension, recent dipyridamole, and caffeine/theophylline not held. Uncontrolled bronchospasm is a hard stop; milder reactive-airway history may steer agent choice toward regadenoson under clinician judgment.

Dobutamine

Dobutamine (β-agonist) raises HR and contractility when vasodilators are contraindicated and exercise is impossible.

Putting Timing Together with MPI

1. Confirm prep (caffeine, meds, consent, IV).
2. Choose exercise vs pharmacologic from order and safety screen.
3. Monitor ECG + BP + symptoms continuously.
4. Inject tracer at protocol peak (exercise peak, mid-adenosine, post-regadenoson, post-dipyridamole window, or peak dobutamine).
5. Recover; reverse drugs if needed; image after the correct delay.

Bottom line: protect the patient first, hit the physiology window second, and document anything that turns a defect into failed stress rather than true ischemia.