Describe and compare the action potentials from cardiac ventricular muscle cells and the sino-atrial node.
This question details an aspect of cardiac physiology which is well described in multiple texts. Comprehensive answers included both a detailed description of each action potential and a comparison highlighting and explaining any pertinent differences. The question lends itself to well-drawn, appropriately labelled diagrams and further explanations expressed in a tabular form. Better answers included a comparison table with points of comparison such as the relevant RMP, threshold value, overshoot value, duration, conduction velocity, automaticity, ion movements for each phase (including the direction of movement) providing a useful structure to the table. Incorrect numbering of the phases (0 – 4) and incorrect values for essential information (such as resting membrane potential) detracted from some responses.
Appropriately labelled diagrams? Tabular form? Who knew that these might be the keys to answering a CICM exam question.
Cell | Ventricular Myocyte | Pacemaker cell |
Resting potential | -90 mV | -60 mV |
Threshold Potential | -70 mV | - 40 mV |
Phase 4 |
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Phase 0 |
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Phase 1 |
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Phase 2 |
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Phase 3 |
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Antoni, H. "Electrophysiology of the heart at the single cell level and cardiac rhythmogenesis." Comprehensive Human Physiology. Springer, Berlin, Heidelberg, 1996. 1825-1842.
Pinnell, Jeremy, Simon Turner, and Simon Howell. "Cardiac muscle physiology." Continuing Education in Anaesthesia, Critical Care and Pain 7.3 (2007): 85-88.
Bers, Donald M. "Cardiac excitation–contraction coupling." Nature 415.6868 (2002): 198-205.
Draper, Morrell Henry, and Silvio Weidmann. "Cardiac resting and action potentials recorded with an intracellular electrode." The Journal of physiology 115.1 (1951): 74-94.
Bers, Donald M. "Cardiac excitation–contraction coupling." Nature 415.6868 (2002): 198-205.
DiFrancesco, Dario. "Pacemaker mechanisms in cardiac tissue." Annual review of physiology 55.1 (1993): 455-472.
Noma, Akinori. "Ionic mechanisms of the cardiac pacemaker potential." Japanese heart journal 37.5 (1996): 673-682.
Grunnet, Morten. "Repolarization of the cardiac action potential. Does an increase in repolarization capacity constitute a new anti‐arrhythmic principle?." Acta physiologica 198 (2010): 1-48.