OBJECTIVE To define the effects of β₂ adrenergic receptor stimulation on ventricular repolarisation in vivo.

DESIGN Prospective study.

SETTING Tertiary referral centre.

PATIENTS 85 patients with coronary artery disease and 22 normal controls.

INTERVENTIONS Intravenous and intracoronary salbutamol (a β₂ adrenergic receptor selective agonist; 10–30 μg/min and 1–10 μg/min), and intravenous isoprenaline (a mixed β₁/β₂adrenergic receptor agonist; 1–5 μg/min), infused during fixed atrial pacing.

MAIN OUTCOME MEASURES QT intervals, QT dispersion, monophasic action potential duration.

RESULTS In patients with coronary artery disease, salbutamol decreased QT_onset and QT_peak but increased QT_end duration; QT_onset–QT_peak and QT_peak–QT_end intervals increased, resulting in T wave prolongation (mean (SEM): 201 (2) ms to 233 (2) ms; p < 0.01). There was a large increase in dispersion of QT_onset, QT_peak, and QT_end which was more pronounced in patients with coronary artery disease—for example, QT_end dispersion: 50 (2) ms baselinev 98 (4) ms salbutamol (controls), and 70 (1) ms baseline v 108 (3) ms salbutamol (coronary artery disease); p < 0.001. Similar responses were obtained with isoprenaline. Monophasic action potential duration at 90% repolarisation shortened during intracoronary infusion of salbutamol, from 278 (4.1) ms to 257 (3.8) ms (p < 0.05).

CONCLUSIONS β₂adrenergic receptors mediate important electrophysiological effects in human ventricular myocardium. The increase in dispersion of repolarisation provides a mechanism whereby catecholamines acting through this receptor subtype may trigger ventricular arrhythmias.