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. 2009:36:105-108.

Electrographic Response of the Heart to Myocardial Ischemia

K K Aras  1 , S Shome  2 , D J Swenson  1 , J Stinstra  3 , R S MacLeod  1
Affiliations

Electrographic Response of the Heart to Myocardial Ischemia

K K Aras et al. Comput Cardiol. 2009.

Abstract

Electrocardiographic (ECG) ST segment shifts are often used as markers for detecting myocardial ischemia. Literature suggests that the progression of ischemia, occurs from the endocardium and spreads towards the epicardium, eventually becoming transmural. Our study with animal models has found the progression of ischemia, characterized by ST elevations to be more complex and heterogeneous in its distribution. We used in situ canine preparations, wherein the animals were subjected to demand ischemia by reducing coronary flow and raising the heart rate through atrial pacing. At reduced flow, increasing the heart rate caused pockets of ST elevations to appear variously distributed in the sub-epicardial, midmyocardial and endocardial regions. Further reduction in coronary flow with simultaneous raising of the heart rate, increased the extent and magnitude of ST elevated regions, that in certain cases became transmural.

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Figures

Figure 1
Figure 1. In situ dog heart with 247 electrode sock and 40 transmural needles inserted into the ventricular walls
Figure 2
Figure 2
17 segment Left Ventricle (LV) model. a, LV anterior view. b, LV posterior view. c, Cross section of the basal region. d, Cross section of the mid region. e, Cross section of the apical region. f, Apex cross section. Each segment spans the full thickness of the LV and the differently colored concentric regions represent the outer sub-epicardium (S), mid-myocardium (M) and the inner endocardium (N)
Figure 3
Figure 3
Development of ST elevated regions in 7M and 7N at flow rate of 30 ml/min and heart rate of 182 bpm. A, Mid region of the LV segmentation model. B, Cross section of the mid region. Two distinct pockets of ST elevations are developing in mid-myocardium and one in the endocardium. C, Color scale: 0-9 mV
Figure 4
Figure 4
Progression of ST elevated regions in 7M and 7N at flow rate of 23 ml/min and heart rate of 182 bpm. A, Mid region of the LV segmentation model. B, Cross section of the mid region. ST elevated regions are increasing in magnitude in the endocardial and mid-myocardial regions of segment 7. C, Color scale: 0-9 mV
Figure 5
Figure 5
Expansion of ST elevated regions in 7M and 7N at flow rate of 16 ml/min and heart rate of 222 bpm. A, Mid region of the LV segmentation model. B, Cross section of the mid region. ST elevated regions have further increased in magnitude. In addition, the two pocket of ST elevations in the mid-myocardium (7M) have now merged to form a bigger ST elevated region. C, Color scale: 0-9 mV
Figure 6
Figure 6
Transmural ST elevation in segment 7 at flow rate of 9 ml/min and heart rate of 222 bpm. A, Mid region of the LV segmentation model. B, Cross section of the mid region. The pockets of ST elevated regions in the mid-myocardium and the endocardium of segment 7 have merged in to a single transmural ST elevated region. C, Color scale: 0-9 mV
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References

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