Computational Intelligence in Cardiology and Heart Disease Diagnosis - Computational Intelligence in Biomedical Engineering - page 170

I V1 V4

VR

II VL V2

V5

III VF V3

V6

QT

Long QT intervals and long distance between
normal beats

Ventricular premature beats

FIGURE 4.21
ECG of ventricular premature beats that is evidenced by long QT inter-
vals and long periods between two normal beat cycles. (Modified from Dean
Jenkins and Stephen Gerred, http://www.ecglibrary.com/ecghome.html.

With permission.)

The normal healthy heart beats between 60-80 beats/min and variations
in this can reflect several disorders. Conditions where the heart beats slower
than 60 beats/min are known as bradycardia (from brady, meaning slow). This
is seldom a problem unless there is prolonged or repeated symptoms such as
fatigue, dizziness, lightheadedness, or fainting. Physically fit individuals have
resting heart rates slower than 60 beats/min. Bradycardia becomes a problem
when there is insucient blood flow to the brain. This condition occurs more
in elderly people and can be corrected by electronic pacemakers to increase
the heart rhythm. It may also occur in patients with atherosclerotic lesions of
the carotid sinus region in the carotid artery.
Tachycardia (from tachy, meaning fast, and cardia, meaning heart) or tach-
yarrhythmia is a condition in which the heart beats too rapidly, for example,
more than 100 beats/min. The beats may be regular or irregular and can
produce palpitations, rapid heart action, chest pain, dizziness, lightheaded-
ness, or near fainting because the blood is circulated too quickly to effectively
service the tissues with oxygen. VT occurs when rapid beating starts in the
ventricles and reduces the heart's ability to pump adequate blood to the brain
and other vital organs. This is a dangerous arrhythmia that can change with-
out warning into ventricular fibrillation , which is one of the most serious
arrhythmias. When ventricular fibrillation occurs, the lower chambers quiver,
and the heart is unable to pump any blood, the patient soon collapses and
sudden cardiac death follows unless medical assistance is provided. If treated
in time, VT and ventricular fibrillation can be changed to normal rhythms
with proper electrical shocks. The characteristic rapid beating can also be
controlled with medications or by locating and treating the focus of rhythm
disturbances. One way to correct this disorder is by using an implantable
cardioverter-defibrillator (ICDs).