Biology Today - May 2018

Heart murmurs

Murmurs are abnormal sounds heard in various parts of the vascular

system. The major cause of cardiac murmurs is due to abnormalities

of the heart valves. It may arise due to improper closing of any heart

valve or in patients with interventricular septal defects that cause

blood flow to be turbulent.

Normally, blood flow through valves and vessels is laminar flow– i.e.,

it flows in smooth concentric layers. Turbulent flow can be caused by :

• blood flowing rapidly in the usual direction through an abnormally
  narrowed valve (stenosis);


• blood flowing backward through a damaged, leaky valve
  (insufficiency);


• blood flowing between the two atria or two ventricles through a small hole in the wall separating them (called a septal defect).

Significance of heart sounds

Heart sounds give valuable information about working of the heart valves. The exact timing and location of the murmur provide the
physician with a powerful diagnostic clue. For example, a murmur heard throughout systole suggests a stenotic pulmonary or aortic
valve, an insufficient AV valve, or a hole in the interventricular septum. In contrast, a murmur heard during diastole suggests a stenotic
AV valve or an insufficient pulmonary or aortic valve.

DIAGNOSTIC TESTS

Human cardiac functioning can be measured by a variety of methods. Moreover, two and three-dimensional images of the heart can
be obtained throughout the entire cardiac cycle.

Echocardiography
Ultrasonic waves are beamed at the heart and returning echoes are electronically plotted by computer to produce continuous images
of the heart. This technique can detect the abnormal functioning of cardiac valves or contractions of the cardiac walls and can also
be used to measure ejection fraction. Echocardiography is a non-invasive technique because everything used remains external to
the body. Other visualisation techniques are invasive.

Cardiac angiography
It requires the temporary threading of a thin, flexible tube called a catheter through an artery or vein into the heart. A liquid
containing radio-opaque contrast material is then injected through the catheter during high-speed X-ray videography. This technique
is useful not only for evaluating cardiac function but also for identifying narrowed coronary arteries.

Electrocardiogram (ECG)

ECG is a graphic record of the electric current produced by the excitation of the
cardiac muscles. Waller (1887) first recorded the electrocardiogram but Einthoven
(1903) studied ECG in details, therefore, he got Nobel Prize in 1924 for the discovery
of ECG. He is also considered “Father of the electrocardiography”.

When the cardiac impulse passes through the heart, electrical current also spreads
from the heart into the adjacent tissues surrounding the heart. A small portion of
the current spreads all the way to the surface of the body. If electrodes are placed on
the skin on opposite sides of the heart, electrical potentials generated by the current
can be recorded; the recording is known as an electrocardiogram (ECG). The
instrument used to record the changes is an electrocardiograph.

A normal electrocardiogram (ECG) is composed of a P wave, a QRS wave
(complex) and a T wave. The letters are arbitrarily selected and do not stand for any
particular words.

The P wave is a small upward wave that indicates the depolarisation of the atria (atrial contraction). It is caused by the activation
of SA node. The impulses of contraction start from the SA node and spread throughout the artia.

Normal open valve Stenotic valve

Laminar flow = Quiet Narrowed valve

Turbulent flow = Murmur

No flow = Quiet Leaky valve

Turbulent backflow = Murmur

Normal closed valve Insufficient valve

Fig.:Heart valve defects causing turbulent blood

flow and murmurs.

P-R interval

= 0.16 sec