Cardiac care. ECG configuration. dr. Kader Kochi.

An electrocardiogram is a graphic representation of the electrical activities (depolarization and repolarization) produced in heart association with each cycle.

The heart is unique among the muscles of body in that it possesses the property of automatic rhythmic contractions. The impulses that precede contraction arise in the conduction system of the heart especially from SA node. These impulses result in excitation of the muscle fibers throughout in atria and ventricles. Impulse formation and its conduction through special fibers make stimulation on contractile cells. The action potentials produced in contractile cells spread through the entire body and reach the skin. the ECG is recorded by applying electrodes to 12 various positions on the surface and connecting these electrodes to the ECG machine, 

when electricity flows towards the positive exploring electrode, the deflection of the stylus of the machine is upwards, i.e., Positive wave. When the electricity flows away from positive exploring electrode the deflection of the stylus will be downwards direction i.e., negative wave. if there is no flow, or impulse is perpendicular to lead, axis there is no deflection. So iso-electric baseline of machine is drawn on graph paper.

Electrical activity consists of two components. Depolarization and repolarization. Depolarization begins from the end of muscle fibre where first excited. repolarisation begin from opposite to end that of first excited. 

Electrocardiogram components.

Waves

P wave, T wave, U wave.

Complex

QRS complex. 

Intervals 

P-R interval, QRS interval, Q-T interval, P-P interval, R-R interval.

Segments

P-R segment, ST segment, T-P segment.

P wave is the wave of atria. It is a compound wave. Repolarisation wave of atria is not visible in graph. 

QRS complex is Depolarization wave of ventricles. T wand U waves are repolarization waves of ventricles. T wave is compound one. T wave should be concordant to qRS wave. (Primary type T wave). Secondary type wave appears opposite to R or S wave when conduction occurred in one way.

Electrical potential of heart traced in ECG are viewed in two planes. 6 view in frontal, vertical plane (6 Limb leads) and 6 view in horizontal plane (6 chest leads). 

There are two methods of ECG analysis. 

1. Systematic analysis of each wave, segment and duration.

2. Simple analysis based on comparison with various diseases pattern.

Systemic analysis of ECG waves

P wave

Normal height:  1 to 2 mm; Normal duration: 0.10 second; Top of P wave is rounded.
P wave  Absent	Aetiology  Atrial fibrillation. S.A block 2:1.  Hyperkalemia.  Junctional or ventricular rhythm.
P-pulmonale P wave  Tall	Aetiology  Right atrial enlargement. It is best seen in LII, and VI. Tricuspid incompetence. Aetiology  Right ventricular hypertrophy. Pulmonary hypertension. ASD left to right shunt. (Ostium primum).
P - mitrale P wave  Wide	Aetiology  Left atrial enlargement. Best seen in LI and AvL. Mitral stenosis. Aetiology  Mitral incompetence. ASD right to left shunt. Wandering pacemaker. Inter atrial block.  Aberrant atrial conduction. Respiratory movement changes.
P wave  Notched	Aetiology  Mitral stenosis. Inter atrial block.
P wave  Inverted	Aetiology  Dextrocardia (aVL). Left atrial ectopic beat (aVL). Retrograde conduction LII (P wave upright in aVR in junctional or ventricular rhythm).  Left atrial enlargement (V1).
P wave Wandering	Aetiology  Atrial fibrosis. SA node diseases. Mitral stenosis.  Hyperkalaemia. Pulmonary vein thrombosis.
P wave  Biphasic	Aetiology  Left atrial hypertrophy (V1).
P wave  Multiple	Aetiology   A.V block 2nd degree type 2. (Aetiology of A.V block Left para sympathetic stimulation, Atrial flutter, atrial rheumatism, beta blockers, Rt coronary artery ischemia, and septal infarction).  Atrial flutter. Carcinoma in chest. Recent atrial myocardial infarction. Thyrotoxicosis. Atrial rheumatism. Blocked atrial premature beat. 3rd degree AV block. Atrial flutter with AV block.

P- R Interval

Normal period is 0.10 to 0.22 second.
PR interval  Prolonged	Aetiology 1st degree A.V block. ASD. Hypothyroidism. Mitral stenosis. Hypokalaemia (Hypokalaemia other changes: tall p and R waves, ST depression, prolonged QT interval, prominent u wave). Hypercalcaemia. Hypermagnesemia. Quinine toxicity. Post ectopic cycle. Cycle following prolonged  Q-T Interval. Rheumatism of heart. Acute infection. Beta blockers. Atrial ischemia. Parasympathetic over activity of left vagus. Anxiety.
P-R interval  Short	Aetiology  Hypomagnesaemia ll ++ (Signs & symptoms are tremor, vasomotor changes and migraine (low serotonin), hypertension & prolonged Q-T interval). WPWS.  Post aberrant cycle. Absence of delay at middle of AV node. Conduction through A.V node by pass.

QRS complex q wave Normally < 1/4 of following R wave, and  duration < 0.03 second. It represents inter ventricular septum  especially of left ventricle.

Q wave

	Aetiology  Old myocardial infarction. Acute myocardial infarction.  Left ventricular hypertrophy (VI-Left posterior wall;V5- septal hypertrophy). Left anterior hemi block( V5-septal depolarization). Pulmonary emboli. Left sided cardio-myopathy ( V5). Deep expiration (LIII). Left ventricular posterior hypertrophy (V2). Left bundle branch block (V1). Pulmonary hypertension (LII). PDA. Amyloidosis.
q wave Absent	It occurs normally at V3( as depolarization perpendicular to V3 electrode). Aetiology  Left bundle branch block (V5). Septal infarction (V5).

R Wave

Amplitude    (Voltage)	Normal amplitude in bipolar lead > 5 mm and < 16 mm. aVL < 12 mm. aVF < 20 mm. V1 < 5 mm. V5 < 25 mm. L1 R+L111 Q = < 21mm. aVL R +V3 R =< 28 mm. V1 S+V5 R   = < 36 mm. V2 S+V6 R   = < 42 mm. R wave height must be progressive from V1 to V5.
VOLTAGE High	Aetiology Ventricular hypertrophy. Left bundle branch block. WPWS. Systemic lupus erythematosus. Acromegaly. Thyrotoxicosis. Nephritis. (Hypokalemia. Aetiology of hypokalemia: tumors, Cushing’s syndrome, aldosteronism, hyper insulinism, diarrhoea and colitis). Fever. Anemia. On expiration. Early ischemia with reactive hyperaemia. Thin chest.
VOLTAGE Low	Aetiology  Pericardial effusion. Pericarditis. Thick chest wall. Emphysema. Diffuse coronary artery disease, hypothyroidism.  Hyperkalaemia. Myocardial infarction some duration. Myocardial fibrosis (Aetiology: ischemia, myocardial rheumatism, Addison’s disease, post infarction). Conditions with para sympathetic over activity. Cardiac depression.
QRS wave Changes in shape	Aetiology  WPWS. Ventricular fibrosis. Bundle branch block. Aberrant conduction.  Ventricular ectopic. Myocardial infarction. Hyperkalaemia. Electric alternans. (Aetiology: pericardial effusion, hyperventilation, following food intake, and anxiety).

S wave

Depth of S wave must be regressive from V1 to V6
S Wave  Deep	Aetiology  Right ventricular hypertrophy (LI, V5). Left ventricular hypertrophy (V1, V2). Left axis deviation (L III). Horizontal position (avf). Vertical position (avl).
S wave Wide	Right bundle branch block (LI, V5).

Q R S Interval

Normal period is 0.04 second to 0.08 second. Ventricular activation time of R wave: < 0.034 second in V1 and < 0.044 second in V5.
QRS interval Wide	Aetiology  Old age. Bradycardia. Hyperkalaemia. Hypocalcaemia. Premature ventricular ectopics (Aetiology of ectopic: tobacco, flatulence, thyroid hormone, toxins, ventricular ischemia, and hypokalaemia).  Aberrant conduction. Ventricular hypertrophy with fibrosis. WPWS. Quinine toxicity. Bundle branch block.  Cardiac depression. Hypermagnesemia. (High Mg++ can induce coronary ischemia, Hyperglycemia, sleepiness, diaphragmatic paralysis and low blood pressure. ECG changes:  prolonged P-R interval, wide QRS interval, and tall T waves).
QRS Interval Short	Aetiology Tachycardia. Hypercalcaemia. Children.

ST Segment

Normally lies at iso-electrical line.
ST segment  Elevation	Aetiology  ST segment convex elevation more than 2 mm: Acute myocardial injury. Recent infarction. More than 2 mm with concave elevation:  Ventricular aneurism. Pericarditis. Chronic rheumatic pericarditis. Thyrotoxicosis. Hyperkalaemia. Sub endocardial infarction (aVR). Leukaemia.  Hypercalcemia (Slurring). Recent myocardial infarction. Elevation less than 2 mm: Asians. Early repolarization. Hypothermia. Pericarditis.
ST segment Depression more than 0.5 mm	Aetiology  Hypokalaemia. Coronary artery thrombosis.  Diabetes mellitus. Hypoferaemia. Ischemia. Left ventricular hypertrophy with strain.  Supra ventricular tachycardia. Sub endocardial infarction. Bundle branch block. Cerebro vascular accident (sympathetic over activity. Pericarditis (in avR)
ST segment Prolongation	> 0.12 second: Aetiology  Hypocalcaemia. Hypo albuminemia. Liver disorders. Children.

T wave

Normally upright in all lead except in LIII, aVR, or V1. its limbs are asymmetrical and height is more than 1/10 of preceding R wave in V5. Normally tall T wave is seen at V3 due to repolarisation begins from far where depolarization ends.
T wave Tall	Aetiology  Hyperkalaemia. Renal failure. Addison’s disease. Right ventricular diastolic overload (V1). Left ventricular diastolic overload (V5). left ventricular hypertrophy. Asians. Ectopic beat left side origin (V5, LI). Posterior myocardial infarction (V2). Recent infarction in reciprocal lead. Acute ischemia with reactive hyperemia.
T wave Flat	Aetiology  After glucose drinks. After carbohydrate food. (Hypokalaemia due to secretion of insulin and subsequent entry of K+ into cell along with insulin). After cold bath. After cool drink. Following low R wave. Emphysema. Hypothyroidism. Ischemia.  Cardiomyopathies. Pericarditis (low R wave amplitude). Equal repolarization potential on both side of electrode.
T wave Inverted	Aetiology:  Ventricular tachycardia.  Hyperventilation (LIII). Atrial tachycardia. After cool drinks.  hypoferremia. After glucose drinks. Anxiety. Childhood. Supra ventricular tachycardia. Horizontal position (LIII). Posterior infarction. Cerebro vascular accident (dysfunction of higher center of autonomic nervous system causes vagus irritation which results parasympathetic activity. so weak stimulation emerges due to inhibition to SA node).  Hypokalaemia. Ventricular hypertrophy. Pericarditis. Cardiomyopathies. Ischaemia. Sub endocardial infarction (symmetrical T wave pattern). Right side origin ventricular ectopic beat (V5). Left bundle branch block. Left ventricular hypertrophy with strain (V5).

Q-T Interval

It is normally in between 0.28 to 0.42 second.  Corrected Q-T Interval (Q-Tc) =estimated Q-T Interval. / square root of R-R interval. Male less than 0.44 second. Female less than 0.46 second.
Q-T interval Prolonged QT interval Short	Aetiology  Cardiac depression. Quinine toxicity. Hypocalcaemia++(Low calcium-Aetiology: low parathyroid hormone, hypo albuminemia - liver & renal disorder. High phosphorus level. ECG changes: Prolonged ST segment, and prolonged Q-T interval). Ventricular hypertrophy. Congenital   prolongation.  Ischemia.  Carditis.   Valvulitis. Autonomous neuropathy. Central nervous system lesion. Cerebro vascular accidents (para sympathetic over activity with weak S.A node stimulation results reactive atrial excitability or sympathetic over activity with rapid atrial rate). Head trauma. Brain tumors. Old age. Bradycardia.  Hypomagnesaemia++. Hypokalaemia+.  Hyponatraremia+ (Low sodium: symptoms are headache, and excess of body water (headache and nausea). ECG changes are similar to hypocalcaemia, hypo albuminemia, hyperkalemia). Aetiology  Exercise. Hypercalcaemia. Digitalis toxicity.   Adrenaline.   Tachycardia. Hypokalemia.

U wave

Normally U wave is developed in same direction of T wave. It is due to repolarisation of the basal part or posterior upper part of left ventricle or posterior septum by strong stimulation or papillary muscles. Best seen in V3 and V6. height < 2mm, <1/3 of preceding T wave.
U wave  Prominent	Aetiology  Hypokalemia. Left ventricular hypertrophy. Cerebro vascular accident (reactive sympathetic over activity increases excitability of posterior surface seen in lead V6 (normally no parasympathetic supply on ventricle). Bradycardia. Hyper thyroid. Digitalis toxicity. Cardiac stimulants. Anterior ischemia with compensatory posterior hypertrophy (V3).
U wave Inverted	Aetiology  Hyperkalaemia. posterior wall ischemia (V6). left ventricular anterior strain(V3).

Heart rate

Normal heart rate is in between 60 -100/ minute. Atrial rate = 60 / P-P interval. Atrial rate = 300 / number of large blocks (0.2 second).          1500 / number of small blocks (0.04 second) in between two p waves. Ventricular rate = 60 / R-R interval. Ventricular rate = 300 / number of large blocks (0.2 second). 1500 / number of small blocks (0.04 second) in between two R waves.
RAPID Regular	Sinus tachycardia: cycle duration < 0.60 second. Etiology  Fever. Thyrotoxicosis. Emotion. Anemia. Beriberi. Para sympatholytic. Sympathomimetics. Liver disorder. Pericarditis. Carditis. Cardiac failure. Low vitamin B1. COPD. Children. *
	Paroxysmal supra ventricular tachycardia (Etiology: Mitral stenosis, hyperthyroidism, ASD, WPWS, emotion, tea, menses and drugs like ephedrine). *
	Paroxysmal atrial tachycardia.
RAPID Irregular	Aetiology  Atrial flutter. Atrial fibrillation.  Idio nodal tachycardia.  Paroxysmal nodal tachycardia.  Idio ventricular tachycardia.  Paroxysmal ventricular tachycardia.
Slow Regular	Sinus bradycardia: cycle duration >1.00 second Aetiology  Athletes. Old age. Hypothermia. Hypothyroidism. Sino atrial node disease. Uraemia. Jaundice. Increased intra cranial tension. Convalescence. Beta-blockers.
	Vagotonic effect. Sympathetic inhibition. S.A block 2:1.
Slow Irregular	Aetiology Sinus arrest. Wandering SA node. Atrial pacemaker. Complete A.V block. Idio- ventricular rhythm.

Heart rhythm

Normal rhythm is sinus regular
Arrhythmia Sinus	Aetiology  Hyperventilation. Hyperkalaemia (Diabetes mellitus, infection, Addison’s disease, burns, ADH and H2O retention)  Cerbro -vascular accident. Atrial ischemia.
Arrhythmia Ectopic beat	Aetiology  Premature ectopic complex appears at early part of cycle. Atrial ectopic. Junctional ectopic.   Ventricular ectopic beat (Aetiology Toxins, Infiltration, Drugs, Hyperkalaemia, Hypokalaemia, Hyperthyroidism, Carcinoma, Ischemia, Tea, Coffee, Meals, Flatulence, Fatigue, Carditis, Sympathomimetics, Old Scar).
Arrhythmia Escape beat	It is physiological and compensatory. Wave complex appear at latter part of cycle. Aetiology  Atrial escape beat.  Junctional escape beat. Bundle branch escape.   Ventricular muscle escape beat.
Arrhythmia	Aetiology  Atrial fibrillation.  Sinus rhythm with occasional SA block 3:2. Sick sinus syndrome.  Wandering atrial pacemaker. Supra ventricular rhythm with AV block. Atrial flutter with irregular AV block. Ventricular tachycardia.
Position Normal heart position in chest is intermediate in vertical view. Upright waves are seen both in aVL and avF
Abnormal Horizontal position	0 degree to -30 degree. Up right waves in aVL. qS wave complex in avF. Aetiology  Central obesity. Flatulence. Left ventricular hypertrophy. Left anterior branch hemi block. Left ventricle anterior myocardial infarction. Aortic incompetence. Old age. Liver hypertrophy. Ascites.
Vertical position	+ 75 degree to +110 degree. qS wave complex in aVL. upright R wave in aVF. Aetiology  Thin chest. Emphysema. Right ventricular hypertrophy. ASD left to right shunt.

Rotation

Normally equal size of R and S wave are seen at V3 It is transitional zone in horizontal plane.
Abnormal   Clockwise  rotation		Aetiology  Low R wave with deep S in V5 (Right ventricular hypertrophy).
Abnormal Anti-clock wise rotation		Aetiology  Tall R wave from septum with less depth of S wave from left ventricle in V1). Left ventricular hypertrophy. posterior wall myocardial infarction. bilateral hypertrophy.

Mean electric axis

Net electrical potential axis normally lies in between 0 to + 90 degree in frontal view. Upright qRS wave complex appear both in LI and LIII.
Left axis deviation of net potential		Upright qRS wave complex in LI and qS wave complex in LIII. Negative axis < -30 degree. Aetiology  Left bundle branch block. Left anterior branch hemi block. Left ventricular hypertrophy. WPWS. Ectopic origin from right ventricle. Anterior myocardial infarction. Normal in 10%.
Right axis deviation		QS wave complex in LI and upright qRS wave complex in LIII. Electric axis > + 90 degree. (>110 degree) Aetiology  Left posterior branch hemi block.  Right bundle branch block. Right ventricular hypertrophy.  Left ventricular ectopic beat. Dextrocardia. Inferior or posterior wall infarction. Children.
ECG changes after exercise
Positive indicatio ns		Ratio of the increases in R wave height and increases in ST segment depression > 1 (Reactive hyperemia). Deep ST depression. Increase in height of T wave. Ventricular premature complex. Reactive tachycardia. Pain after exercise.