Electrical Alternation in Experimental Coronary Artery Occlusion

Abstract

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Hysteresis and bistability in the direct transition from 1:1 to 2:1 rhythm in periodically driven single ventricular cells

“…[3][4][5][6][7][8][9][10][11] On the clinical electrocardiogram, alternation of either the ST-segment or the T-wave ͑or both͒ has been the most commonly described form of alternans during ischemia. 5,6,8 Indeed, instrumentation to check for occult T-wave alternation in the clinical electrocardiogram using power spectral analysis is presently being evaluated in an attempt to identify patients at an increased risk of sudden cardiac death ͑CH 2000 Cardiac Diagnostic System, Cambridge Heart Inc.͒.…”

“…[3][4][5][6][7][8][9][10][11] On the clinical electrocardiogram, alternation of either the ST-segment or the T-wave ͑or both͒ has been the most commonly described form of alternans during ischemia. 5,6,8 Indeed, instrumentation to check for occult T-wave alternation in the clinical electrocardiogram using power spectral analysis is presently being evaluated in an attempt to identify patients at an increased risk of sudden cardiac death ͑CH 2000 Cardiac Diagnostic System, Cambridge Heart Inc.͒. 8 The alternation in the T-wave of the electrocardiogram may be due to an intrinsic beat-to-beat alternation in the action potential duration in the ischemic area, being essentially equivalent to the ''primary'' alternans 47 seen in a periodically stimulated isolated ventricular cell 25,27,28 and in ionic models of space-clamped ventricular membrane.…”

“…10 47 Recent modeling work with the LR model supports the secondary origin of the alternans in ischemia. 68 There are instances in which alternans first appears during ischemia immediately after a spontaneous or externally elicited premature ventricular contraction 5,6,9 or following a single intentionally inserted long cycle. 9 The most obvious possibility to account for this finding is that there is bistability between 1:1 rhythm and primary alternans in the ischemic area, as can occur in maps derived from ionic models.…”

“…14 ͔ It is thus possible that when ''triggered alternans'' 9 follows a premature ventricular contraction, the premature stimulus is flipping an area showing marginal 1:1 conduction to 2:1 conduction, thus inducing secondary alternans in the surrounding area ͑or vice versa, abolishing alternans͒. 5,6,9 In addition, spatially discordant alternans ͑alternans in anti-phase at two locations͒, which is more malignant than concordant alternans, 10,11,21 can be transformed into the latter during ischemia by a premature ventricular contraction ͑ei-ther spontaneous or stimulated͒, a reduction of the BCL for one cycle, or a pause. 7 Again, it is possible that flips between 1:1 and 2:1 rhythms might somehow be involved: e.g., if the out-of phase alternans seen during discordant alternans is secondary ͑i.e., each of the two types of alternans is associated with its own area of 2:1 block͒, flipping one area of 2:1 block to 1:1 rhythm would result in a conversion from discordant to concordant alternans.…”

“…When the ability of ventricular muscle to conduct the action potential is sufficiently compromised ͑by, e.g., ischemia, hyperkalemia͒, this 1:1 rhythm is lost and replaced by some new rhythm, such as Wenckebach block, 1,2 2:1 block, 3,4 alternans rhythm, [3][4][5][6][7][8][9][10][11] or even complete block. 3 Alternatively, if one paces healthy multicellular ventricular muscle at a fast enough rate, one can also obtain 2:1 rhythm [12][13][14] or alternans rhythm.…”