Electrocardiography Review: A Case-Based Approach

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The model represents ischemic conditions at 10 minutes after onset phase Ia, stage 2. The left ventricular wall of all three datasets was divided using the segment AHA scheme [ 27 ]. To run the study, hemispheric ischemic regions were placed at the center of each AHA segment. The center of the hemispheres was located at the endocardial surface of the myocardium as subendocardial myocytes need more oxygen due to stronger contraction and are therefore perfused more intensely [ 28 ]. Owing to this circumstance and because of the greater distance to the coronary arteries, electrophysiological changes can be first observed in the subendocardial layer after the onset of ischemia [ 29 ].

This situation is called subendocardial ischemia. If the occlusion lingers, ischemia spreads transmurally towards the subepicardium [ 30 ]. As soon as the entire wall is affected, the term transmural ischemia is used. As the values for the extent of the BZ that can be found in the literature vary significantly [ 31 , 32 ], three series of simulations were carried out using different BZ radii: The time increment for the CA simulations was set to 0.

TMVs obtained through the CA simulations were interpolated on tetrahedral meshes in order to carry out electrical field finite element calculations. Extracellular potentials on the body surface of the respective anatomies BSPMs were computed using the bidomain model as in [ 25 ].

The conductivity tensors and were set according to [ 33 ]. Aberrations larger than 0. As pointed out in the introduction, it is challenging to detect the ST segment and especially the point in ECG analysis. Also, the previously defined ST deviation is sensitive towards interference with the QRS or T wave in case of even slight errors in the timing of annotations. We therefore propose the definition of a point as substitute for the point. The point is then defined as the time step for which this envelope signal is minimal see Figure 1.

This work investigates the limitations of different electrode setups in representing ST deviations caused by myocardial ischemia. This scenario will be more feasible than BSPM during emergencies; however, it assumes that the location for this additional electrode is known for a specific subject. We investigated if such an optimal position can exist, that is, if it is consistent across subjects by mapping the individually optimal positions to the other 2 thoraces. The scenario was not considered for the STSD as the improvement by looking at the whole BSPM as compared to the lead ECG was already limited; thus, the benefit of just one additional electrode was negligible.

Thus, the highest physiological deviation was the same in all scenarios including at least the lead electrodes. Figure 2 shows the detection rates obtained for certain STSD thresholds when looking at different sets of lead signals spanning all subjects. The threshold defines the minimum STSD according to 1 which needs to be observed for a given set of leads to classify an ECG as ischemic. This approach was chosen as the question of finding the optimum threshold balancing sensitivity and specificity cannot be answered by this study. In general, subendocardial ischemia was harder to detect than transmural ischemia.

Detection rates for transmural setups were higher by 1. Findings for transmural ischemia are not biased by the volume of the ischemic region. Different BZ sizes had only little effect on detection rates. However, the smaller the BZ, the easier the detection of ischemia.

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Looking at the 3 different subject models, detection was the easiest for subject , followed by and VM in all lead systems. Rates for VM, , and were Details are shown in Table 2.

For small ischemia radii, the position did not differ significantly from the one in the physiological signal. For setups with , the K point moved towards the T wave in most cases. Figure 3 shows the KPD-based detection rates for the different lead systems. However, the gain in detection rate by adding these four additional electrodes was always less compared to adding one additional electrode whose position had been optimized for a given subject.

Please note that this electrode position was the same for all ischemia radii, locations, and BZ extents. The additional improvement by looking at the remaining several hundred electrodes of the BSPM was limited to less than 2. It was most beneficial for higher threshold values, though.

Using a subject-specific location for the 10th electrode Figure 3: Figure 4 shows the position of the individually best electrode locations and the best common position. As the aim of this work is to evaluate the sensitivity capability of different lead systems, the presented results focus on KPD. In brief, Figure S1 in the Supplementary Material available online at http: Figure 5 shows that adding further electrodes to the lead ECG achieved higher detection rates mostly for small and medium ischemia radii.

Larger ischemic regions were easier to detect than smaller ones using KPD as well. Compared to subendocardial setups, detection rates for transmural setups were higher by 3. The effect of the BZ size was, again, small. Average detection rates were The BZ dependencies of additional electrode related improvements were insignificant. Considering the different subjects, ischemia was the hardest to detect in VM. Adding additional electrodes increased detection rates the most in subject K.

The scenario yielded a detection rate increase of 0. Figure 7 shows the average detection rates considering the KPD in only a single lead at a time. The temporal position of the point was determined using all 12 leads for this analysis. For Figure S2 in the supplementary material, only point elevation was considered.

The sensitivity focus pivoted towards lateral AHA segments in the midapical layers for more lateral Wilson leads through for pure point elevation. When also considering point depression Figure 7 , additional sensitivity in opposite segments, particularly in the midbasal layers, resulted in a less distinct pattern compare, e. While apical detection rate was high in all leads when considering KPD, it was significantly above average only for the contiguous limb leads II, aVF, and III, as well as and when only considering K point elevation.

Looking at the detection rates subdivided by AHA segment did not reveal a significant pattern considering absolute detection rates as well as improvements by introducing additional leads. Segments 8 and 14 were calling for lower thresholds, hence harder to detect, and segments 4, 16, and 17 were easier to detect than average.

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However, the curves for different subjects did not intersect, thus showing comparatively constant interindividual differences. In this work, a comprehensive in silico study was performed to test the sensitivity of BSPMs against the lead and the 3-channel ECG in detecting acute myocardial ischemia at 10 minutes after onset phase Ia, stage 2. Also, the question was investigated whether right-sided Wilson leads or a single additional electrode would improve sensitivity for the lead ECG, assuming the ideal case that its position can be known.

It was then studied if such an ideal position can be found that is valid across subjects. Our results regarding the right-sided Wilson leads underline the results in [ 34 ] and may explain why little clinical validation exists on their effect [ 11 ]. This also implies that a single additional electrode with ideal placement could not possibly improve detection rates significantly. One potential reason for these differences is that, in contrast to clinical works, detection rates in this study were computed with respect to the possible variants of the studied ischemic events at an equal distribution, not with respect to their occurrence in the presenting patient cohort.

More importantly, we were looking at early ischemia at 10 minutes after onset in this study which differs significantly from the time when clinical ECGs are typically acquired. On the one hand, this is not surprising due to their larger heart surface and thus signal. On the other hand, this finding seems to contradict the results by Wilhelms et al. Principles of Cardiovascular Radiology E-Book.

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Echo Made Easy International Edition. Editorial Reviews Review "This book will serve as both an excellent study guide in preparing for certification and as a reference in reviewing key concepts in the interpretation of electrocardiograms. Product details File Size: Up to 4 simultaneous devices, per publisher limits Publisher: January 20, Sold by: Share your thoughts with other customers. Write a customer review. Showing of 2 reviews.

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It gives comprehensive explanations for each ECG but unfortunately it doesn't cover all topics.

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