Why we use it
Isoproterenol is a synthetic catecholamine that hits beta-1 and beta-2 receptors with essentially no alpha activity. The result: increased heart rate, increased contractility, and arteriolar vasodilation. In the EP lab we exploit two things — sinus rate acceleration to bring out otherwise dormant arrhythmias, and dropping AV-node refractoriness to make supraventricular re-entry circuits easier to trigger.
Indication in the lab
- SVT induction when programmed stimulation alone fails to initiate the clinical tachycardia
- PV reconnection testing after pulmonary vein isolation — does a dormant connection light up under adrenergic drive?
- Trigger mapping in AF ablation — non-PV triggers from coronary sinus, SVC, LAA may surface only on Iso
- Idiopathic / outflow tract VT and PVC ablation when ectopy is sparse at baseline
- Inappropriate sinus tachycardia / POTS testing
- Temporary chronotropic support for severe bradycardia when pacing isn’t immediately available (rare in EP, more a crash-room use)
Dose and route
- Standard provocation: start 1–2 mcg/min, titrate up.
- High-dose challenge: 20 mcg/min for 3–5 minutes after PV isolation is a common protocol.
- Maintenance for trigger mapping: 4–10 mcg/min, often paired with burst pacing.
- Given as a continuous IV infusion via pump, ideally through a central line or large peripheral with a clean carrier.
Dilution matters — every lab has a standard concentration (commonly 2 mg in 250 mL D5W = 8 mcg/mL). Confirm with the bag label before starting.
Onset and duration
- Onset: within 1–2 minutes of starting the infusion.
- Steady-state: 5–10 minutes at a given rate.
- Offset: drug effect dissipates within 5–10 minutes of stopping; useful when we need to “reset” between provocation runs.
Monitoring
- Continuous ECG with rhythm strip running
- Continuous arterial BP (cuff if no A-line)
- SpO2 and EtCO2
- Watch for the expected drop in diastolic BP — coronary perfusion lives there
- Document HR, BP, rhythm at baseline, at each titration step, and when arrhythmia inducts
Side effects to watch for
- Sinus tachycardia / palpitations — expected, but uncomfortable for the awake patient
- Hypotension — beta-2 vasodilation; usually responds to slowing infusion and fluids
- Myocardial ischemia — increased demand + dropped diastolic pressure; chest pain or ST changes mean stop
- Tremor, anxiety, headache in awake patients
- Hypokalemia with prolonged use — drives K into cells
- Pro-arrhythmia — the whole point sometimes, but watch for sustained VT or hemodynamically unstable rhythms
Contraindications and cautions
- Active ischemia or recent ACS
- Significant aortic stenosis or hypertrophic obstructive cardiomyopathy
- Digitalis toxicity (already pro-arrhythmic)
- Severe uncorrected hypovolemia
Reversal
There’s no specific reversal. Stop the infusion — most effects resolve within minutes. Refractory tachycardia or hypotension may need:
- IV fluids
- A short-acting beta-blocker (esmolol) if the patient stays tachy and symptomatic
- Phenylephrine for pure alpha support if needed
Common pitfalls
- Bag concentration error — double-check whenever a new tech mixes the bag.
- Running Iso at high doses through a small peripheral that infiltrates.
- Forgetting to stop the infusion before sheath pull and watching the heart race in recovery.
- Calling the case “non-inducible” without an adequate Iso challenge.