Abnormal T Waves

The Normal T Wave

The T wave represents rapid repolarization (phase 3 of the action potential). The normal T wave is asymmetric with a gradual slope followed by a steeper slope. Normal T waves are upright in almost all leads. T waves can be inverted or biphasic in leads III, V1, and V2. The T wave is most often concordant with the QRS wave because the T-wave axis is normally within 45 degrees of the QRS axis in adults.

Ischemic T-Wave Changes

Hyperacute T Waves

In hyperacute ischemia, the duration of the action potential is shortened, resulting in early repolarization and amplification of the normal T wave. Hyperacute T waves have a broader base than the “peaked T waves” of hyperkalemia. Hyperacute T waves are one of the earliest ECG abnormalities to occur in myocardial infarction. T waves are generally considered hyperacute if they are greater than 10 mm in amplitude in precordial leads or greater than 5 mm in amplitude in limb leads.

T-Wave Inversions

Non-ST Elevation MI

Unstable Angina

Prior MI

T-wave inversions can indicate non-ST elevation MI and unstable angina. They may also be chronic footprints of a past myocardial infarction. The terminal aspect of the ischemic T wave is the first to become inverted, followed by the middle and initial portions after acute infarction. When only the terminal portion of the T wave is inverted, the T wave appears biphasic. Ischemic TW inversions are typically symmetric and narrow (Fig. 7.1; Table 7.1).

FIGURE 7.1 Progression of T-wave changes after acute myocardial infarction.

Pseudonormalization

T waves that were previously inverted may become less inverted, flat, or upright during acute ischemia. This is thought to be secondary to acute shortening of the action potential duration.¹

FIGURE 7.2 T-wave changes suggestive of pseudonormalization.

TABLE 7.1

	Hyperacute T Wave	Peaked T Wave
Setting	Acute myocardial infarction	Hyperkalemia
ECG Appearance
ECG Features	Wide based	Narrow based
Location	Localized to several leads	Generally diffuse

deWinter’s T Waves

This T-wave pattern in precordial leads is associated with near-complete occlusion of the proximal LAD.²

ST Segment Depression

The J-point is depressed, and the ST segment is upsloping.

Tall T Waves

Associated T waves are tall and symmetric.

FIGURE 7.3 Appearance of deWinter’s pattern.

Wellens’ Syndrome

Wellens’ syndrome refers to recent angina coupled with a characteristic pattern of T-wave inversions that represent a critical lesion in the left anterior descending artery. These T-wave changes most likely represent a previous complete LAD occlusion (transient STEMI) followed by reperfusion.

These changes are located in the electrocardiographic distribution of the LAD (leads V2-V4) and consist of deep symmetric T-wave inversions or biphasic T waves.

Criteria for Wellens’ Syndrome³

Prior History of Angina

Characteristic T Waves

Biphasic or deeply inverted T waves in V2 and V3.

Normal Precordial R-Wave Progression

Minimal or No Elevation of Cardiac Markers

Minimal or No ST Elevation

Absence of Pathologic Q waves in Precordium

ECG Features

Biphasic T Waves (A Pattern)

Upsloping followed by downsloping of the T wave; usually associated with some ST elevation.

Symmetric TWI (B Pattern)

Deep, symmetric TW inversions.

FIGURE 7.4 A, B. Different T-wave morphologies in Wellens’ syndrome.

Timing of ECG Findings

Wellens’ T waves more commonly occur when patients are free of chest pain. In the setting of chest pain, these T waves may normalize or the ST segments may become elevated. Biphasic T waves and terminal T-wave inversions also occur in a majority of patients who have had successful reperfusion of the myocardium supplied by a previously occluded left anterior descending artery.³

Management

An exercise stress test is contraindicated. These patients may die of cardiac arrest on the treadmill. They should bypass a stress test and undergo urgent cardiac catheterization.

Prognosis

In a study performed by Wellens, 75% of patients with a Wellens’ pattern who failed to undergo angiography went on to develop extensive anterior wall myocardial infarctions in a mean of 8.5 days.⁴

LV Strain Pattern

ST depression and T-wave inversion are commonly seen in patients with left ventricular hypertrophy. This reflects repolarization abnormalities in the thickened left ventricle myocardium. ST depression is minimal and downsloping, running into the gradual descent of the inverted T wave.

ECG Changes

These changes occur in the left precordial (V5 and V6) and limb (I and aVL) leads. ST depression and T-wave inversion present in other leads should raise suspicion for myocardial ischemia. A potential pitfall would be to attribute TWIs present in inferior limb leads or diffusely in the precordium to left ventricular strain.⁵

T-Wave Morphology

T waves are asymmetric. Gradual downslope and more abrupt upslope.

ST Depression

In leads with tall R waves, the ST segment is depressed and blends with the inverted T wave.

FIGURE 7.5 Appearance of LV strain pattern in leads with tall R waves.

Mechanism

Depolarization from the endocardium to the epicardium is prolonged in the hypertrophied left ventricle. Depolarization is prolonged enough for the endocardium to become repolarized before the entire myocardium is completely depolarized. Repolarization proceeds from the endocardium to the epicardium. This results in ST depression and T-wave inversion.

FIGURE 7.6 Depolarization and repolarization patterns in normal versus hypertrophic ventricle. In normal ventricle, (A) depolarization and repolarization vectors are in opposite directions. Despite the opposite directions of these vectors, the QRS and T waves are in the same direction because they represent opposite electrical events (ions flowing in opposite directions). In the hypertrophic left ventricle, (B) these electrically opposite events proceed in the same vector directions. The T wave is therefore opposite in direction to the QRS wave in the hypertrophied heart.

Digitalis Effect

Inverted or flattened T waves following scooped and depressed ST segments are electrocardiographic signs of a patient taking digitalis. They reflect earlierthan-normal repolarization of myocardial cells. These changes occur in patients with normal therapeutic levels of digoxin and do not indicate digoxin toxicity.

Morphology

Mild ST Depression

ST depression can mimic myocardial ischemia. ST depression has a scooped appearance (Fig. 7.7).

Flat or Inverted T waves

Shortened QTc Interval

Reflects faster repolarization.

Increased U-Wave Amplitude

Location

These changes are most prominent in the lateral precordial leads.

Persistent Juvenile T-Wave Pattern

T-wave inversions may be a normal finding in children and can persist into adulthood, more commonly in women than in men. T-wave inversions in this pattern can be associated with J-point ST elevations.

Location

These changes occur in leads V1-V3.

Hyperkalemia

The earliest electrocardiographic sign of hyperkalemia is the presence of peaked T waves. These T waves are typically narrow-based and symmetric. They reflect faster repolarization caused by this electrolyte abnormality. See Chapter 8 for more information about the ECG changes associated with hyperkalemia.

Location

These changes are usually diffuse and are most prominent in the precordial leads (Fig. 7.9).