Alterations in endocardial activation of the XXXX papillary muscle early and late after myocardial infarction.

@entity227 @entity39 @entity235 @entity63 @entity1563 @entity1188
Permanent @entity1563 produces time-dependent changes in surviving subendocardial cellular properties. We compared the functional alterations in Purkinje (P) and ventricular muscle (VM) activation early (24 hr) and late (4 weeks or greater) after permanent @entity1563 in an in vitro preparation of @entity235 papillary muscle. High-density extracellular (1 to 2 mm resolution) and selected intracellular recordings were made in five animals early and seven animals late during stimulation of a free-running P strand. Activation patterns of P and VM layers from @entity63 and unaffected papillary muscles were compared in the same animal. Average P layer conduction velocity was determined in normal and @entity63 regions with the use of a linear array of recording and stimulating electrodes. Purkinje activation was altered little in the early phase of @entity1188 , while healing was associated with a generalized 25% reduction in P layer conduction velocity and localized block and fragmentation of P waveforms. Intracellular recordings at sites of nonsynchronous P activation revealed electrotonic interaction between cell groups. At 24 hr, small groups of VM were present but with abnormal activation patterns in regions of @entity39 with fragmented and delayed extracellular waveforms produced by partially uncoupled groups of cells. Local delay and block could be modulated by rate and site of stimulation. After healing, VM activation abruptly stopped at the @entity227 , marked by a characteristic "end potential." These studies demonstrate important differences in the functional attributes of the P and VM layers studied early and late after @entity1563 . Alterations in cell-to-cell relationships are likely very important in determining abnormalities of activation in both settings.
