Computational Intelligence in Cardiology and Heart Disease Diagnosis - Computational Intelligence in Biomedical Engineering - page 158

(j)

(a) (d) (g)

J Point

U

T

(k)

(e)

S − T

(h)

(b)

(c) (i)

(f)

FIGURE 4.11
ST wave segments in the ECG. (Reprinted with permission from Julian,
D.G., Campbell-Cowan, J., and McLenachan, M.J., Cardiology , Saunders,
Edinburgh, New York, 2005.)

0.16 s). In patients with heart disease, especially with scarred or inflamed
heart tissue, a longer PR interval may be observed as more time is required
for the depolarization wave to spread through the atrial myocardium and
the AV node. Shortened PR intervals could mean that the impulse originates
in the junctional tissue or could be due to the Wolff-Parkinson-White syn-
drome (Julian et al., 2005).
The ST segment is a further interval important for detecting a variety
of CVDs (see Figure 4.11). It usually appears as a levelled straight line
between the QRS complex and the T wave. Elevated or depressed ST seg-
ments (depending on the ECG lead being observed) is a sign of MI as the
heart muscle is damaged or does not receive sucient blood, causing a distur-
bance in ventricular repolarization. Pericarditis can be detected by observing
ST segments that are concave upward over many cardiac cycles. In digitalis
therapy it has been found that ST segments are depressed with a gentle sag-
ging, whereas the T wave remains normal or flattened. ST depressions can also
indicate ventricular hypertrophy, acute myocardial ischemia, and sinus tachy-
cardia, but the shape of the depressions are characteristic of the pathology.
The QT interval is approximately 0.35 s and provides important information
about the state of ventricular contractions. Its duration shortens as heart rate
increases and usually the QT interval does not exceed half the time between
the previous RR interval for rates between 60 and 90 beats/min. This interval
is sometimes dicult to measure because it cannot be clearly identified. Never-
theless, prolonged QT intervals can indicate the risk of ventricular tachycardia
(VT) or the presence of certain drugs such as antidepressants.