The myocardial clearance of rubidium may be obtained by praecordial counting after a single intravenous injection of Rb86Cl The following study uses this isotopic method, and examines the effects of lignocaine on the coronary blood flow in patients with recent myocardial infarctions. MethodsThe praecordial counting was performed with a 5 x 5 cm NaI(Ti) scintillation detector with a lead collimator, I50 mm long with an external diameter I10 mm. Pulses from the detector were fed via a pulse height analyser to a digital ratemeter and then to a recorder. For 131I activity the pulse height analyser was set for the 364 KeV photopeak with a ioo KeV window. For 86Rb, the pulse height analyser was set for i o8 MeV with a I00 KeV window. The ratemeter time constant was set at 4 seconds for recording background and at 4 seconds during the procedures. The chart speed was set at 3 cm per minute. Blood activity was measured in a 5 cm welltype scintillation detector with the pulse height analyser setting as described for external counting of 131I and 86Rb.The counts are corrected for the relative inefficiencies in the in vivo and in vitro systems, introducing a coefficient in calculated from the counting rates obtained when two soo-ml flasks containing known concentrations of 131I and 86Rb are counted externally under a standard geometrical arrangement.-(c.p.m./ml) 131I (well) xc.p.m. 86Rb(flask) n (c.p.m./ml) 86Rb (well) x c.p.m. 131I (flask) .... (I) Experimental procedureThe experiments were performed in the morning on resting subjects in the supine position. A Cournand

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The myocardial clearance of rubidium may be obtained by praecordial counting after intravenous injection of Rb-minus 86 Cl. Eight patients with recent myocardial infarction had this determination performed before and after the infusion of 10 mg phentolamine at a rate of 0.3 mg/minute. The average predrug myocardial clearance of Rb was 89.3 plus or minus 29.9 ml/min per 100 g myocardium. After phentolamine, the average myocardial clearance rose to 117.3 plus or minus 33.3 ml/min per 100 g myocardium (P LESS THAN 0.01). An explanation for this findings is presented as well as its possible clinical applications.

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