Subepicardial ischaemia

The ECG pattern of subepicardial ischaemia, is more consequence of previous ischaemia than due to the presence of active ischaemia. On the contrary, the ECG pattern of predominant subendocardial ischaemia (symmetric and usually taller-than-normal positive T wave accompanied by rectified ST segment and prolongation of QTc interval) represents the first ECG change induced by active ischaemia (Figure 3.7). 

In the VCG the T wave of subepicardial ischaemia, which is the only one that is usually recorded because the T wave of subendocardial ischaemia is very transient, presents a T loop of homogeneous inscription and frequently small and more or less rounded, although it may be very narrow in some planes (Figure 3.17). 

Figure 3.9 In case that in basal state a certain degree of ischaemia with subendocardial predominance exists too mild to produce clear ECG changes, an increase of active ischaemia still with subendocardial predominance will produce an ST-segment depression (subendocardial injury pattern) (A). If as a consequence of ischaemia there is a delay in repolarisation predominating in subepicardium or being transmural, a flattened or negative T wave appears in leads with, but also without, predominant R wave (B-1) (subepicardial ischaemia pattern). The latter pattern is...

We should remember that in some chronic coronary patients, those who present a transmural infarction classically named inferoposterior but with the new classification we define as inferolateral MI (Figure 5.9B(3)), a tall, frequently peaked, and in this case persistent, T wave may be recorded in V1-V3 as a consequence of the changes that the transmural infarction produced in repolarization (mirror pattern of inferobasal and lateral subepicardial ischaemia) (Figure 3.10). 

Figure 3.10 (A) ECG with a typical pattern of chronic subepicardial ischaemia in the leads facing the inferior wall (negative T wave in II, III and VF) and the lateral wall (positive peaked T wave in V1-V2). There is a necrosis in the same area in which a QR complex in II, III and VF and an RS complex in V1 are recorded. (B) Horizontal axial...

Electrocardiographic pattern of subepicardial ischaemia (transmural) diagnosis and differential diagnosis... 

The ECG pattern of subepicardial ischaemia -flattened or negative T wave - is observed in IHD (Table 2.1), but it may also appear in other situations (see Table 3.2). We have to remember that the ECG pattern of subepicardial ischaemia (negative T wave) although may probably be due to real active ischaemia (ACS), more often appear in the dynamic changes of some ACS as a reperfusion pattern or is explained by the changes that MI has induced in ventricular repolarisation (chronic Q-wave MI) (p. 37 and Table 8.1). 

We will discuss the diagnostic and location criteria. The clinical presentation and prognostic implications of the ECG pattern of subepicardial ischaemia in different clinical settings of IHD will be discussed in Part II of this book (p. 289). 

In Figure 3.17 different examples of T waves of subepicardial ischaemia together with their corresponding VCG loops are presented. It is of particular interest to observe the homogeneous inscription of ischaemic T loop as compared to a normal T loop, which presents a slower first part of inscription, whether closed or opened (Figure 3.2). 

Figures 3.18 and 3.19 show the evolution of two Mis from the acute phase with a huge ST-segment elevation until the appearance of Q wave of necrosis and negative T wave of subepicardial ischaemia. In Figure 3.20, a patient with chronic MI of inferior wall presents in the same ECG a different grade of ECG pattern of subepicardial ischaemia (negative and deep T wave in inferior leads, tall and positive T wave in right precordial leads as a mirror pattern and flat T wave in V6).

Figure 3.17 (A) and (B) ECG-VCG correlation of the T wave and the T loop of subepicardial ischaemia in two patients with myocardial infarction (A) of the inferior wall and (B) of the inferior and lateral walls. Observe that a T loop in both cases shows homogeneous inscription and is directed upwards (see FPa) in the first case and upwards and forward in the second case (see HPa). The QRS loop of (A) rotates only clockwise and of (B) rotates first clockwise and later counter-clockwise. In the first case inferior Ml is isolated and in the second, associated to superoanterior...

C) ECG-VCG correlation of the T wave and T loop in case of subepicardial ischaemia of anteroseptal zone. Observe how the T loop with homogeneous inscription (symmetric negative T wave in ECG) and a QRS loop that is directed backwards and to the left with counter-clockwise direction and the T loop backwards and to the right (see HPa). 

On the other hand, an evident U wave (Figures 3.24 and 3.25) or even a less obvious one (Figure 3.26) in the presence of a positive T wave is equivalent to subepicardial ischaemia (Reinig, Harizi and Spodick, 2005). 

Subepicardial ischaemia (primary repolarisation alteration) is frequently associated with LVE or LBBB (secondary repolarisation alteration), wherebymixed patterns are generated (Figure 3.27). 

The negative T wave of subepicardial ischaemia is recorded in different leads, depending on the myocardial area affected by the occluded coronary artery (inferolateral or anteroseptal). In general, in case of single-vessel disease ischaemia is regional therefore, a mirror pattern may be observed in the FP (Figures 3.10 and 3.20). Much probably, ischaemia at rest is usually explained by only a culprit artery, even maybe stenosis in other arteries (multivessel disease). 

It is difficult to define the strict diagnostic criteria that will assure that we are in front of a T wave with an ECG pattern of subepicardial ischaemia. Nevertheless, we consider that this diagnosis may be done in the following circumstances ... 

Figure 3.25 (A) Basal ECG (V1-V6) with ECG pattern of important subepicardial ischaemia in a 65-year-old patient with daily crisis of variant angina that always appeared at the same hour. During a crisis (B,C), there is pseudonormalisation of the ST segment with an evident negative U wave. A few seconds later, the ECG returns to...

Figure 3.28 A patient with chronic constrictive pericarditis. The T wave is negative in many leads, but not quite deep, without the mirror pattern in the frontal plane. The T wave is only positive in VR and V1 because as this is a diffuse subepicardial ischaemia, they are the only two leads in which the ischaemia vector that is directed away from the ischaemic area is approaching the exploring electrode.

In first part we have discussed the criteria for diagnosis and location of ST-segment elevation (pattern of subepicardium injury) and ST-segment depression or negative T wave (pattern of subendocardial injury and subepicardial ischaemia). Now we will discuss the clinical evolution, prognostic implications and risk stratification of these patterns. 

ECG pattern of subendocardial ischaemia and the pattern of subepicardial ischaemia. Slight ST-segment elevation may be noted in V1 lead. (B) Few hours later appeared typical pattern of subepicardial injury (ST-segment elevation) with QS of necrosis in V2-V4. 

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