Conduction of the Cardiac Impulse

Abstract

Depressed excitability and responsiveness were created in excised bundles of canine Purkinje fibers. A segment 8 mm long was depressed by being encased in agar containing 47 mM K + , the ends of the bundle outside the agar remaining normal. Either normal end could be excited through extracellular electrodes. Action potentials were recorded by intracellular microelectrodes at each end and within the depressed segment. Conduction velocity within the depressed segment fell as low as 0.05 m/sec. Abnormalities of impulse transmission through the depressed segment included delay, 2:1 block, higher degrees of block, rate-dependent block, and block showing the Wenckebach phenomenon. Asymmetries of conduction seen included one-way block. Action potentials in the depressed segment were of low amplitude and showed slow upstrokes. Variations in action potential duration occurred in the depressed segment when conduction failed or was very slow and when impulses were dropped. Delay in conduction too great to result simply from a slow upstroke is attributed to summation of excitatory events across regions of block in a syncytium of cells. The results prove that conduction delays great enough to permit re-entry can occur in short segments of Purkinje fibers subjected to high K+.

Lamr1 functional retroposon causes right ventricular dysplasia in mice

“…The difficulty in generating lethal tachyarrhythmia in mice, due to the high beating rate and small size of their hearts 19 , might explain our failure to detect lethal arrhythmia. KK/Rvd mice showed electric conduction inhomogeneity leading to prolonged QRS duration, which is often seen in humans with ARVD 20,21 .…”

Quinidine-induced action potential prolongation, early afterdepolarizations, and triggered activity in canine Purkinje fibers. Effects of stimulation rate, potassium, and magnesium.

“…The solution was bubbled with a 95%02-5% CO2 mixture, and the temperature was maintained at 37±0.50 C. Transmembrane potentials were recorded from both ends of the Purkinje strand with glass microelectrodes filled with 2.7 M KCl (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) Qohm DC resistance) connected to a high-input impedance amplification system (World Precision Instruments, New Haven, Connecticut). The amplified signals were displayed on a Tektronix oscilloscope (Beaverton, Oregon) and photographed with a Grass kymographic camera (Quincy, Massachusetts) or recorded on an eightchannel tape recorder (Vetter, Rebersberg, Pennsylvania).…”

Effects of pacing on triggered activity induced by early afterdepolarizations.

“…2 In contrast to delayed afterdepolarizations, EADs are increasingly likely to occur at slow rates of stimulation. 12 This characteristic of EADs, along with their tendency to occur more readily during conditions of prolonged repolarization, has led to the suggestion that EADs may induce bradycardia-dependent arrhythmias as well as arrhythmias associated with the long QT syndrome . 22 It is unclear whether EADs and the arrhythmias they induce can be differentiated from those automatic rhythms that occur in cardiac fibers with low membrane potentials.…”