Abnormal ECG

The normal ECG is composed of P wave QRS complex and T wave. 

P wave is caused by electrical potential generated when atria depolarized before artrial contraction begins.

The QRS complex is caused by potential generated when ventricles depolarizes before contraction that is as the depolarization wave spread through he ventricles thus both P wave and QRS complex are depolarization waves.

T wave is due to re polarization of ventricle muscles.

Abnormalities in P wave:

Variation in the duration, amplitude and morphology of ‘ P ’ wave helps in the diagnosis of several cardiac problems. such as .

1. Atrial fibrillation:

Mainly fibrillation means a small, local involuntary, muscular contraction due to spontaneous activation of single muscle cells or muscle fiber whose nerve supply has been damage or cut off. In these disease when the ECG of patient are taken, the P wave is not present .  Atrial muscle mass separated from the ventricular muscle mass by fibrous tissue. Therefor ventricular fibrillation often occur with out atrial fibrillation.

A frequent cause of atria fibrillation is atrial enlargemnt resulting from heart valve lesions (any patholological dis continuetity of tissue or loss of function of heart) that prevent atria from wmptying into ventricle. Or from ventricular failure with excess damming of blood in the atria.

Atrial fibrillation may be caused by hypertension. Diabetese millitus, congestive heart failure, age above 75 years.

Atrial fibrillation : P wave is not present.

B . Atrial proxysmal tachycardia :

To diagnose this disease in Ecg we must know following things.
1. Proxysmal: An arrhthmia (irregular heart beat) that suddenly begin and end

2. Tachycardia: Abnormal rapid heart rate usually 160-190/ min

When the ECG of patient which have atrial proxysmal     tachycardia disease is taken, a sudden ioncrease in heart rate from about 95-150 beat per minute . On close study of ECG during rapid heart beat an inverted P wave is seen before QRS –T complex and this P wave is partially superimposed onto normal T wave. This indicate that origion of proxysmal tachu cardia is in the atrium, but because of abnormal P wave shape , the origon is not near Sinus node.  

The proxysmal tachycardia of ten result from an aberrant rhythm that involves the A-V node .

This usually cause almost normal QRS-T complexes but totally missinh or obscured P wave . Atrial or AV nodal proxysmal tachycardiaboth of which are called supraventricular tacchycardia , both of which  occure in young , other wise helathy people and they genrally grow out of the predispoition (a latent susceptibility to disease that may be activated by uinder certain condition ) to tachy cardia after adolescene ( the period b/w puberty and completion of physical growth from 11-19 years ) . a person tremendously and may cause weakness during the paroxysmal only seldom does permanent harm from the heart.

c. Hyperkalemia: P wave is small.

D. Sinoatrial Block:

Sinoatrial disease result form degeneration of the sinus node and is common in the elderly. It may present with palpitation ( subjective sensation of an rapind or irregular heart beat) , didzzy spells or syncope ( suddend loss of conscioussness, without warning due to cerebral anemia caused by obstruction to cardiac arrhythmia ) due to intermittent tachycardia , brady cardia or pauses (interpretation in the sinus rhthym , which is not exact in normal cardiac cycle) with no atrial or ventricular activity. In sinoatrial block P wave is absent.

SA block

E. Right atrial hypertrpohy :  P wave is tall

F. Left atrial hypertrpohy: P wave is tall and broad.

2. QRS complex:

It is causeed by potential generated when the ventrical depolarize before contraction i-e as the depolarization waves spread through ventricle
a. Purkinji system block:                                 When these fibers are bllocked the cardiac impulse must then be conducted by ventricle muscle instead of by way of the purkinji system. This decrease the velocity of the impulses conduction about 1/3^rd of normal. In purkinji system Block QRS complex are prolong.

B. Current of injury:

Many different cardia abnormalities specially those that damage the heart muscle cells itself, often cause part of the heart to remain partially or totallt depolarized all the time. When this occur curent flows b/w the pathologically depolarized and normally polarized areas even b/w heart beat. This is called current of injury. The effect of injury on heart muscle cause the random ECG especially QRS complex.

T wave : the T wave is caused by potential repolarization of ventricle after contraction.T wave become hyperaccute (Tall and broad) that reffer to acute myocardial ischemia, pericarditis, myocardial infraction.

P-R interval:

The distance b/w P and R waves  is very important for many diseases such as bradycardia in which heart is very slow less then 60 and the distance b/w P and R is large, and also in first degree heart block. 

The distance is very short in tachycardia , wolf- parkinson –white syndrome, duchene muscular dystrphy, lawn-levine syndrome and type two glycogen storage disease.

Ecg in tachycardia P-R interval is shortened heart rate is more then 100 per minute

Q-T interval :

This interval indicate the ventricular depolarization and ventricular repolarization. It is prolong in heper calcimia , hypocalcimia , myocarditis. It is shortened in isoelectric period.

S-T Segment:

S-T segment prolonged in hypocalcimia and it is shortened in hypercalcimia. The hypo calcim,ia is indicate the less amount of calcium, the calcium has important function in the contraction of cardia muscle. And Hypercalcimia mean large large amount of calcium. Variation in S-T segment that elevation occur in left bundle branch block anda cute pericarditis.

Written by Abid Abdullah
Student of First prof
Pharm-D

University of BAlochistan .
Hope it helped