Walter gaskell and the understanding of atrioventricular conduction and block
Mark E. Silverman, MD, MACP, FRCP, FACCa,b,* and
Charles B. Upshaw, Jr, MD, FACP, FACCa,b
a Departments of Medicine, Emory University School of Medicine; Piedmont Hospital, Atlanta, Georgia, USA
b Department of the Fuqua Heart Center, Piedmont Hospital, Atlanta, Georgia, USA
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Figure 1 Walter Holbrook Gaskell (reprinted with the permission of Cambridge University Press and reproduced by the Wellcome Library, London).
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Figure 2 Walter Holbrook Gaskell on the left and assistant with crocodile in the Cambridge Physiological Laboratory. Gaskell employed young crocodiles from Ceylon in his studies on the cardiac effects of the vagus and sympathetic nerves. (From Franklin, KJ. Joseph Barcroft, Oxford: Blackwell, 1953. Reprinted with permission of Blackwell Science LTD and reproduced by the Wellcome Library, London.)
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Figure 3 Appearance and measurements of the tortoise heart when excised and suspended, February 27, 1882 (13). (I) Measurements before Gaskell began the experiment. (II) Measurements after experimental cutting of the right atrium by Gaskell, dividing it into two parts, As and Av. We measured pulse rates, cardiac intervals, atrial and ventricular pulse wave durations and ventricular pulse wave amplitudes from the atrial and ventricular tracings of Figure 4 before and after the experiment. After cutting deeply into the right atrium, 2:1 AV block develops between As and Av. The As pulse rate remains 7.5 beats/min, but the Av and V pulse rates fall to 3.75 beats/min. The V pulse wave amplitude and duration increase with the ventricular bradycardia due to the increased ventricular stroke volume. The As-Av interval increases 0.7 s after the atrial cut, whereas the Av-V interval increases 1.0 s and alternate Av and V pulse waves are blocked. The beginning of the As pulse wave is obscured by the V pulse wave; it is assumed that the As pulse wave duration is the same as the measured Av pulse wave duration. A = right atrium; As = pulse wave of the atrium near the sinus venosus; Av = pulse wave of the atrium near the AV groove; As-Av interval = time from the onset of the As pulse wave to the onset of the Av pulse wave; Av-V interval = time from the onset of the Av pulse wave to the onset of the V pulse wave; As-V interval = time from the onset of the As pulse wave to the onset of the V pulse wave. B = upper part of the tortoise body; F = forceps attached to the aorta; L = two silk ligatures with hooks at one end (one ligature is tied to the right atrium and the other is tied to the apex of the ventricle; the two hooks are attached to levers of the kymograph); S = sinus venosus; V = ventricle. The figure has been lightly retouched for clarity.
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Figure 4 Selected segment of polygraph tracings of February 27, 1882, from Figure 4, Plate III of study by Gaskell (13), from the right atrium and ventricle of a tortoise with our laddergram added, showing in panel I a heart rate of 7.5 beats/min and stable 1:1 AV conduction. In panel II, recorded after cutting deeply into the right atrium, 2:1 AV block develops; the As pulse rate remains 7.5 beats/min, the Av and V pulse rates are 3.75 beats/min, and alternate Av pulse waves are absent. The laddergram depicts 1:1 AV conduction in panel I and 2:1 AV conduction in panel II. On the atrial tracing, numbers 1 through 9 represent sequential As pulse waves, and the numbered Vs under the V pulse waves refer to connected V waves; Av pulse waves follow odd numbered As pulse waves but are absent after each even numbered As pulse wave. In panels I and II, As, Av and V under the tracing are printing by Gaskell at the end of the respective pulse waves. On the ventricular tracings, the numbered Vs represent sequential ventricular pulse waves and correspond to the numbered Vs of the atrial tracing. On the laddergram, numbers 1 through 9 above the top line refer to sequential As pulse waves and correspond to the numbers above the atrial tracing. A = atrial pulse wave; AV = interval between the atrial and ventricular pulse waves; V = ventricular pulse wave; see Figure 3 for other abbreviations. Time line above the laddergram has notches at 2 s intervals; arrows point in the direction of impulse propagation; paper speed by our measurement is 1.15 mm/s. The figure has been lightly retouched for clarity.
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