beta(2) Adrenergic receptors mediate important electrophysiological effects in human ventricular myocardium

Objective-To define the effects of beta (2) 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 beta (2) adrenerg ic receptor selective agonist; 10-30 mug/min and 1-10 mug/min), and intrave nous isoprenaline (a mixed beta (1)/beta (2) adrenergic receptor agonist; 1 -5 mug/min), infused during fixed atrial pacing. Main outcome measures-QT intervals, QT dispersion, monophasic action potent ial duration. Results-In patients with coronary artery disease, salbutamol decreased QT(o nset) and QT(peak) but increased QT(end) duration; QT(onset)-QT(peak) and Q T(peak) -QT(end) intervals increased, resulting in T wave prolongation (mea n (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 i n patients with coronary artery disease-for example, QT(end) dispersion: 50 (2) ms baseline v 98 (4) ms salbutamol (controls), and 70 (1) ms baseline v 108 (3) ms salbutamol (coronary artery disease); p < 0.001. Similar respo nses 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-<beta>(2), adrenergic receptors mediate important electrophysio logical effects in human ventricular myocardium. The increase in dispersion of repolarisation provides a mechanism whereby catecholamines acting throu gh this receptor subtype may trigger ventricular arrhythmias.