Topic : Correlation of ECG and Heart Sounds

Introduction :

Blood enters the arterial system from the ventricles of the heart in a pulsatile manner. However, when blood is leaving the arterial system through the capillaries, it flows continuously. Between contractions, when heart is relaxed and blood is not being pumped into the arterial system, there is still enough pressure in arterial system to move blood along arteries. The pressure in arterial system exists because the elasticity of arteries allow them to distend and recoil and function as a pressure reservoir.

In this article you will record ECG from a subject and listen to the characteristic “ lub-dub “ heart sounds. The “lub” sound occurs during the early phase of ventricular contraction and is produced by closing of atrioventricular valves, which prevents blood flow into atria. When the ventricles relax, the blood pressure drops below what is in the artery and the semilunar valves close, producing “dub” sound.

ECG and its briefing :

. ECG stands for Electocardiogram.

· It’s a recording of heart’s electrical activity.

· It is useful in demonstrating heart’s pathology.

· ECG records heart’s rhythm and activity on a moving strip of paper on a screen.

The P Wave :

The first wave on an ECG is P wave, indicating atrial depolarization in which atria contract. The P wave is first wave on ECG because action potential on for heart is generated in the Sinoatrial node located on atria. Increased or decreased P waves can indicate potassium ion concentration in body that will alter nerve activity. A missing P wave indicates atrial fibrillation, a cardiac arrhythmia in which heart beats irregularly, preventing efficient ventricular diastole.

The QRS Wave :

The QRS complex refers to a combination of Q, R and S waves and indicates ventricular depolarization and contraction. The Q and S waves are downward waves and R wave is an upward wave. The QRS complex represents action potential moving from AV node. Abnormalities in QRS complex may indicate cardiac hypertrophy.

T Wave and ST- segment :

The T wave indicates ventricular repolarization, in which ventricles relax following depolarization and contraction. The ST segment refers to gap between S wave and T wave and represents time between ventricular depolarization and repolarization. An elevated ST segment is a classic indicator for myocardial infarctions, though missing or

downward slopping ST segment may indicate myocardial ischemia.

Ventricular Fibrillation :

When ECG output shows no identifiable P waves, QRS complexes or T waves, it indicates ventricular fibrillation, a severe arrhythmia. During ventricular fibrillation, heart beats extremely fast and irregularly and can no longer pump blood. Ventricular fibrillation will cause sudden cardiac death within minutes unless electrical resuscitation is performed immediately. It generally occurs with heart failure and is thought to be caused by action potential that re-enters AV node through muscle fibres.

Heart Sounds :

· Heart sounds produced by beating heart.

· These are usually listened by a stethoscope.

First Heart Sound :

· It is produced by closure of atrioventricular valves at beginning of Systole.

o Soft

· Rheumatic fever

· Heart failure

o Loud

· Mitral stenosis

· Anemia

· Pregnancy

o Variable Intensity

· Complete heart block

· Atrial fibrillation

Second Heart Sound :

· It is produced by closure of semilunar valve at end of systole.

· Aortic valve close before pulmonary valve.

o Wide split

· Pulmonary stenosis

· Pulmonary hypertension

· Right bundle branch block

o Wide and fixed split

· Atrial septal defect

o Reversed Split

· Severe aortic stenosis

· Hypertrophic cardiomyopathy

o Loud P2

· Pulmonary hypertension

Third Heart Sound :

· Low frequency sound in early diastole.

· S3

· May be normal

· Ventricular dysfunction

· Pregnancy, Anemia

· Left to right shunts

Fourth Heart Sound :

· Low frequency sound in late diastole.

· S4

· LV S4- aortic stenosis, systemic hypertension, coronary artery disease

· RV S4- pulmonary stenosis, pulmonary hypertension

Abnormal Heart Sounds :

Heart sound is also called murmur. There are two kinds of heart murmur : innocent or abnormal.

o Systolic Murmur :

· Normal (innocent murmur)

· Ejection across semilunar valve

· Regurgitation across AV valves

· Ventricular septal defect

o Diastolic Murmur :

· Always abnormal

· Aortic or pulmonary regurgitation

· Mitral or aortic stenosis

Conclusion :

Electrocardiography is an interpretation of the electrical activity in the heart. Contractions of atria are initiated near the end of ventricular diastole, which is initiated by depolarization of atrial myocardial cells (sinoatrial node).