A.E. Marble

Effects of Oral Amiodarone on Left Ventricular Function in Dogs: Clinical Implications for Patients with Life-Threatening Ventricular Tachycardia

Twenty-four mongrel dogs were divided into two equal groups to determine the effects of orally administered amiodarone on left ventricular function. Measurements of left ventricular function included left ventricular contractility as denoted by maximum rate of rise of left ventricular pressure (dP/dtmax), cardiac index (CI), left ventricular stroke work index (LVSWI), and peripheral vascular resistance (PVR). Left ventricular function was measured in 6 of the 12 animals in Group 1 before and after 14 days of amiodarone administered orally; the remaining animals served as controls. The dP/dtmax was reduced from 2,855 to 1,291 mm Hg/sec (p less than 0.01), and LVSWI fell from 1.6 to 0.74 gm-m/beat/kg (p less than 0.05) in the 6 animals given amiodarone. The 12 animals in Group 2 underwent 30 minutes of ischemic arrest. Six animals in Group 2 underwent 30 minutes of ischemic arrest. Six animals were given amiodarone orally for 14 days prior to cardiopulmonary bypass and ischemic arrest; the other 6 served as controls. Before cardiopulmonary bypass, the dogs administered amiodarone had significantly greater depression of dP/dtmax (p less than 0.01) and LVSWI (p less than 0.05). Thirty minutes of ischemia produced significant depression of left ventricular function in all animals in Group 2. However, a significantly greater reduction in dP/dtmax and LVSWI occurred in those animals receiving amiodarone. Furthermore, 4 of the 6 dogs receiving amiodarone were unable to sustain sufficient cardiac output following cardiopulmonary bypass to permit long-term survival (p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Simulation of coronary artery revascularization

Simulation of the commonly constructed geometries of aorto-coronary bypass anastomoses was carried out using especially fabricated distensible tubes and a pulsatile pump. The system pressure was maintained between 80 and 120 mmHg. The total mean flow was set at 250 ml min-1 (Reynolds number of 200) and the pulsatile frequency was varied from 0 to 2 Hz. A water-glycerine mixture having a density and viscosity similar to that of blood was used throughout. A 16 mm film of the front of black dye injected proximal to the anastomosis was made as the dye approached and passed through the anastomosis. Anastomotic geometries consisted of: end to side, parallel, 45 degree angle, and 90 degree angle. Stenoses, located in the tube representing the coronary artery, were simulated using a bevelled insert which represented an 80-85% area reduction. Flow visualization revealed that distensible tubes gave more realistic flow patterns than rigid tubes, a result particularly evident when a stenosis was present. Pulsatile flow demonstrated considerably more mixing than steady flow. The use of pulsatile flow in distensible tubing with a partial stenosis showed retrograde flow through the stenosis which was not evident for either steady flow or for flow in rigid tubing. The flow at the anastomatic site of the graft having an angle of 0 degrees showed a jetting action with a zone of recirculating fluid being present whereas for a 90 degree graft a distinct helical flow was formed distal to the anastomosis.

Spectral Analysis of Small-Amplitude Electrical Activity in the Cold Potassium-Arrested Heart

Recent reports have suggested that small-amplitude electrical activity may persist following the administration of potassium cardioplegia. This report confirms the presence of small-amplitude electrical activity in the potassium-arrested heart and describes a canine model that may be used to measure microvolt plunge-electrode potentials during ischemic arrest. Thirty-one adult mongrel dogs were placed on cardiopulmonary bypass and underwent 90 minutes of ischemic arrest. The heart was arrested with 10 ml per kilogram of body weight of crystalloid cardioplegia (20 mEq of KCl/L) at 4 degrees C. Core temperature was maintained at 26 degrees C and myocardial temperature, within a range of 8 degrees to 10 degrees C with topical ice-slush saline solution. Cardioplegic solution, 10 ml/kg, was reinfused every 30 minutes during the 90 minutes of ischemia. Electrical activity and transmural temperature were continuously monitored over the anterior surface of the left ventricle with specially designed plunge electrodes. Visual electrical and mechanical activity ceased in each animal after the infusion of cardioplegic solution, and was associated with an isoelectric electrocardiogram. However, microvolt (10(-6)V) small-amplitude electrical activity was recorded at a myocardial temperature of 10 degrees C in each animal during ischemic arrest, and the activity from 6 animals was stored on magnetic tape. Spectral analysis of electrical activity during cardioplegic arrest indicated that the fundamental frequency of small-amplitude electrical activity was in the range of 3.25 Hz. These data confirm the presence of small-amplitude electrical activity in the cardioplegia-arrested heart at 10 degrees C.

Impedance spectroscopy: An accurate method of differentiating between viable and ischaemic or infarcted muscle tissue

AbstractThe object of the paper is to present results that show that impedance spectroscopy is an accurate method of assessing the condition of muscle tissue. Specimens of muscle tissue were excised from 36 Atlantic salmon and subjected to impedance spectroscopy measurements made at intervals during an 8h period of ischaemia and necrosis. These measurements were conducted for three different temperatures and for both the longitudinal and the transverse orientations of the muscle fibres. The specimens were also subjected to ATP, pH and visco-elastic measurement and analysis to establish the degree of correlation between changes in these quantities and impedance spectroscopy parameters due to ischaemia. It was concluded that the mean relaxation time,

Prevention of myocardial electrical activity during ischemic arrest with verapamil cardioplegia.

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THE MEASUREMENT OF AFTERLOAD, VASCULAR INPUT IMPEDANCE, AND POWER DISTRIBUTION IN AORTO- FEMORAL BYPASS

was the impedance spectroscopy parameter that best described the changes taking place in the muscle tissue during the post-mortem period, decreasing by 60–76% during the 8h. This was the case for all three temperatures and for both orientations. Furthermore, the muscle tissue changes due to ischaemia, as reflected in the decrease in the mean relaxation time

Simulation of Aorto Coronary Bypass Anastomoses Flow Conditions Using Distensible Tubing and a Pulsatile Pump

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