Debra A. Angello

Ribose infusion accelerates thallium redistribution with early imaging compared with late 24-hour imaging without ribose

To determine if early (4-h) thallium-201 imaging with ribose infusion would enhance detection of thallium redistribution better than late (24-h) imaging without ribose infusion, 15 patients with coronary artery disease underwent thallium stress tests by both methods within 2 weeks. All 15 patients had quantitative coronary angiography. After immediate postexercise planar imaging during the first of two exercise tests, patients were randomized to receive either intravenous ribose (3.3 mg/kg per min) or a control infusion of saline solution for 30 min. Images performed at 4 h for the ribose study were compared with those at 24 h for the saline control study. During the second test, exercise was carried to the same rate-pressure product and each patient received the opposite infusion. Four-hour postexercise images after ribose infusion identified 21 reversible defects not seen in the 24-h saline study. Three reversible defects were seen only in saline studies, but not with ribose at 4 h (p less than 0.01); 15 reversible defects were seen with both tests. When analyzed with respect to the 31 vascular territories supplied by a coronary artery with a greater than 50% stenosis, 8 territories had reversible defects present in the ribose but not the saline study and the saline study did not demonstrate reversible defects in territories that were seen in the ribose study (p less than 0.01). In 14 of these territories, reversible defects were seen with both tests. In 6 of 15 patients, additional vascular territories with reversible defects were identified after ribose infusion. It is concluded that ribose enhances the detection of thallium redistribution at 4 h compared with 24-h control images in patients with coronary artery disease and, therefore, substantially improves the identification of viable ischemic myocardium.

Characterization of chronically implanted ventricular endocardial pacing leads

The expected implant lifetime of pacemaker generators has been extended with the introduction of lithium power sources. Consequently, the pacing lead may become the component that determines the total implant lifetime of the pacemaker. This fact emphasizes the necessity for accurate assessment of the integrity of a chronically implanted lead. In this study, chronic threshold and impedance data from 61 patients having the same type of ventricular endocardial lead for up to 10 years were retrospectively analyzed. The mean acute current threshold was 0.81 +/- 0.33 mA. The chronic current threshold had a range of between 1 and 5 mA, which was approximately two to five times greater than the acute implant value. Chronic voltage threshold and impedance were 0.7 to 4 V and 335 to 775 omega, respectively. The findings of this study provide general guidelines for chronic lead parameters and illustrate some of the difficulties encountered in gathering and interpreting long-term lead data.

Acute Effect of Lidocaine on Coronary Blood Flow and Myocardial Function

The acute effects of lidocaine on coronary blood flow, hemodynamic parameters, and wall function were studied in 14 anesthetized pigs. Lidocaine was infused intravenously as a bolus (dosage range from 1.5 to 4.0 mg/kg). At ten to thirty seconds after infusion, coronary blood flow reached 154±38% (mean±SD) of the baseline resting flow (p < 0.001). The double product, an estimate of myocardial oxygen demand, decreased from a baseline value of 9221 ±2174 to 8008±1923 mmHg beats/min (p<0.01). Sixty seconds postinfusion myocardial function decreased from baseline wall thickening of 46±25% to 41±17% (p=0.04). An acute bolus of lidocaine appears to transiently increase coronary blood flow, by decreasing coronary vascular resistance, and also decrease myocardial function. Thus, an acute lidocaine bolus may favorably alter the myocardial oxygen supply/demand ratio.

Principles of Electrical Testing for Analysis of Ventricular Endocardial Pacing Leads

MPROVEMENTS in lithium power sources for cardiac pacemakers have extended the potential implant lifetime of a pacing system beyond ten years.’ Problems related to the electrode-lead component of the permanent pacing system, therefore, are becoming increasingly important. Certain electrical parameters characterizing the integrity of the electrode-lead can be measured while it remains implanted. To promote an understanding of these electrical parameters, this review presents an analysis of the physical and electrical principles underlying cardiac pacing. The analysis has been formulated to facilitate an understanding of the essence and limitations of numerical data provided by currently available pacing system analyzers, which are testing devices designed to simplify routine parameter measurements. An annotated procedure for “trouble-shooting” an implanted pacing lead is also presented.

Effect of lignocaine on coronary blood flow, systolic myocardial function and myocardial high energy phosphate stores in swine.

1. To investigate the effect of lignocaine upon coronary blood flow, myocardial systolic wall function and high energy phosphate stores, lignocaine was administered as a rapid intravenous injection to 14 open chest anaesthetized swine.