About PQRST in ECG

P wave: ECG deflection representing atrial depolarization. Atrial repolarization occurs during ventricular depolarization and is obscured.

QRS wave: ECG deflection representing ventricular depolarization.

T wave: ECG defection representing ventricular repolarization

ECG

P Wave in ECG

P wave is the result of depolarisation of left and right atria. It is upright in leads, I, II, AVF and V2-V6, diphasic or inverted in other leads.

Q Wave in ECG

A small physiological Q wave is seen in I, II, AVF and V₄-V₆. Its duration is less than 0.03 second and its height is less than one-forth the height of accompanying P wave. Abnormal Q wave only in AVF or AVL has no diagnostic significance. A Qs complex in V1, V2 is very often a normal finding.

   Low Voltage QRS Complexes

(1)Myxedema,

(2) Pericardial effusion,

(3) Emphysema,

(4) Hypopituitarism,

(5) Thick chest wall,

(6) Incorrect Standardisation.

    Significance of Q Wave in Lead III 

(1) Normal variant,

(2) Inferior infarction,

(3) Acute Pulmonary embolism,

(4) A negative delta wave,

(5) Left posterior hemiblocks,

(6) Vagotonia.

Differential Diagnosis of Abnormal Q Wave

Myocardial infarction

Myocardial infiltration / trauma

Ventricular hypertrophy

Septal hypertrophy

LVH, RVH

Conduction defects : LBBB and LAHB

Dextrocardia

R and T waves in ECG

R wave when dominant in AVL implies horizontal heart position and in AVF, vertical heart position. T wave is variable in III, AVL and VI, inverted in AVR and always upright in all other leads. Children and young adults may have normally T inversion in V1-V3.

       Tall R in V1

(1) RBBB,

(2) RVH,

(3) True posterior infarction,

(4) Type AWPW syndrome,

(5) HOCM,

(6) Duchene’s muscular dystrophy,

(7) Dextrocardia

ST Segment

ST depression of 0.5 mm or elevation upto 1 mm is normal provided there is no T wave changes. ST elevation greater than 1 mm in chest leads without T wave changes is a feature of early repolarisation.

ST Elevation

Early repolarization,

Myocardial infarction,

Pericarditis,

Prinzemetal angina.

ST Depression

Ischemic heart disease (Subendocardia) ischaemia),

Digitalis and Quinidine, bundle branch block, ventricular hypertrophy, electrolyte disturbance (hyperkalemia), myocarditis and cardiomyopathy, Mitral Valve Prolapse (MVP), cerebral hemorrhage,hyperventilation, reciprocal change in right precordial leads in posterior wall AMI.

Ta Segment

Ta segment depression more than 1 mm is due to atrial hypertrophy, dilatation, intra atrial block or pericarditis. Ta segment elevation occurs in atrial infarction or atrial perforation as during cardiac catheterization.

    Causes of  T Wave Inversion

(1) Ischaemic Heart Disease (IHD)

(2) Myocardial infarction

(3) Ventricular hyprtrophy with strain

(4) Apical cardiomyopathy

(5) Anxiety (DaCosta Syndrome)

(6) Mitral valve prolapse (II, III, aVF),

(7) Marfan Sybdrome (II, III, aVF),

(8) Persistent Juvenile Pattern

    Tall T Waves in Precordial Leads

(T Wave Height > 10 mm)

(1)  Myocardial ischaemia,

(2) Apical infarction,

(3) Hyperkalemia,

(4) Cerebrovascular accident,

(5) Vagotonia,

(6) LV diastolic over load.

     Methods of Normalize T Wave Variants

ECG recording to be in

(1) Fasting State,

(2) Erect Posture,

(3) Following hyper ventilation,

(4) After exercise / atropine,

(5) After inducing bradycardia by propranolol,

(6) After potassium intake.