ELECTROCARDIOGRAM

ELECTROCARDIOGRAM – Normal Conduction System of Heart, Purpose of ECG, Components of ECG, ECG Graph Sheet, Heart Rate, Rhythm, Blocks, Axis, Hypertrophy, Electrolyte Disturbance in ECG, Myocardial Infarction, 12 Lead ECG, Lead Placement, Indications of 12 Lead ECG, Cause of Abnormal ECG Pattern, Preparation of the Patient, Preprocedural Care, Procedure, After Care and Nurses Responsibility (NURSING PROCEDURE)

Electrocardiogram (ECG) is invented by Enthovan in 1901. It is a permanent record of the electrical activity of the heart. It is a tracing made of the various phases of the heart action by means of an electrocardiography. It is a graphical representation that describes about the heart

The electrocardiogram is an instrument which detects very small electrical signals, generated by depolarization and repolarization of the myocardium. Electrodes are attached to the limbs and chest of the patient, and electrical changes are amplified and recorded on a moving paper

NORMAL CONDUCTION SYSTEM OF THE HEART

The electrical impulse is generated in the sino-atrial node (pacemaker) of the heart. it spreads through the both atria and cause atrial contraction. It crosses the atrioventicular node and is passed down through right and left bundle branches and finally reaches the Purkinje fibers, where the ventricular contraction take place

PURPOSE OF ECG

• Electrocardiogram is the most important signal tool for the diagnosis of arrhythmias
• It is helpful to study the cardiac functions – rate, rhythm, and axis
• It helps to diagnose cardiac disease condition – myocardial infarction, injury, ischemia and hypertrophy
• It helps to detect electrolytes imbalance hyperkalemia
• To give valuable diagnostic information about cardiac function
• To confirm the coronary heart disease in most cases
• To demonstrate cardiac arrhythmias such as ventricular tachycardia and heart block

COMPONENTS OF ECG

Electrocardiography consists of waves, complexes and intervals

• Wave or complex: it is a deflection that can be positive or negative wave-atrial depolarization QRS complex-ventricular depolarization. T wave – ventricular repolarization
• Segment: A is the period of time between a wave or complex, e.g. ST-segment
• Interval: an interval is the time between two points on the ECG, e.g. PR- interval
• Time duration (normal) for the P-wave – 0.08 seconds PR-interval less than 0.20 seconds (average 0.16 seconds), QRS complex 0.08 seconds, ST segment – 0.12 seconds and T-wave – 0.16 seconds

ECG GRAPH SHEET

• ECG tracing are recorded on graph paper, which is divided into small (1/1 mm) squares light lines and large (5/5 mm) squares by heavier lines
• Horizontal lines (Y-axis) measures the amplitude (voltage), one small square represents 1 mm and a large square represents 5 mm or 0.5 mm
• The vertical lines (X-axis) measure time, each small square represents 0.20 seconds

HEART RATE

• Normal heart rate is 60 to 100 beats per minutes, less than 60 beats per minute called bradycardia and more than 100 beats per minutes called tachycardia
• The heart rate per minute is equal to the number of large squares between the R-waves divided into 300, e.g. if there are two large squares between the R-waves 300 divided by 2 = 150 beats per minutes
• Count the number of small squares between R-R intervals and divide. When the heart rhythm is irregular, count the QRS complexes in 6 seconds and multiply the number by 10 to get the patient’s heart rate per minutes (30 large block are equal to 6 second)

RHYTHM

• Atrial rhythm measures the distance between two consecutive P-waves (P-P interval). If the distance between all the P-waves are same, the atrial rhythm is regular
• Ventricular rhythm measures the distance between the two consecutive R-waves (R-R interval)
• Sinus tachycardia – heart rate is more than 100 beats per minutes with normal PQRST waves
• Sinus bradycardia – heart rate is less than 60 beats per minutes with normal PQRST waves
• Premature atrial contraction (PAC) RR-intervals vary with a compensatory pause after the PAC
• Paroxysmal atrial tachycardia (PAT) heart rate is 150 to 250 per minutes, P-wave are difficult to recognize. QRS complexes are normal in shape
• Atrial flutter – P-waves form saw tooth pattern, there are more than one P-wave between two consecutive   QRS complexes
• Atrial fibrillation – no regular P-wave, P-wave appearing as a wavy baseline
• Paroxysmal junctional tachycardia – heart rate is 150 to 220 beats per minutes, P-wave are either absent or appear inverted

BLOCKS

• Sino-atrial blocks (SA block) occasional long pauses between R-R complexes
• First degree AV block: P-R interval is prolonged beyond 0.20 second
• Second degree AV block (Mobitz type 1 or Wenckebach) P-R interval is progressively prolonged until finally as QRS complex is dropped. Second degree AV block (Mobitz type II) A QRS complex is present after every 2^nd, 3^rd, 4^th wave
• Third degree AV block (Complete heart block) P wave, do not have any relation with QRS complexes
• Right bundle branch block (RBBB): M-shaped QRS complexes in lead V1, V2, QRS complexes measure more than 0.12 second in width and are above the isoelectric line in lead Vi. Broad and slurred S-wave in lead VS and V6
• Left bundle branch block (LBBB): M-shaped QRS complexes in leads V5 and V6. QRS complexes prolonged more than 0.12 second and are below the isoelectric line in lead V1. Deep S-wave in leads V1 and V2
• Premature ventricular contractions (PVCs): No P-wave, QRS complexes are wide and bizarre with T-wave in opposite direction
• Ventricular tachycardia: No P-waves, QRS complexes are wide and bizarre and resemble PVC in succession
• Ventricular fibrillation: A wavy baseline, no discernable QRS complexes. Ventricular asystole – no wave pattern, usually only a flat line present

AXIS

• It refers to the direction of depolarization which spreads throughout the heart to stimulate the myocardium to contract
• Vector: it shows the direction in which most of the stimulus is traveling. QRS vector is always AV node. QRS vector-normally points downwards and to the patients left side
• We can locate the position of the QRS vector with in a large cycle around the heart. The center point is AV node. QRS vector changes in hypertrophy (vector is less than 90 degree angle)  and infarction (vector is more than 90 degree angle)
• Normal axis: QRS vector shows left downwards points in 0 to 90 degree angle. Lead 1 QRS vector right side called positive vector and left side called negative vector. Lead 1 positive called normal axis
• AVF lead shows lower half is positive and upper half is negative. The AVF positive vector is the normal axis
• Normal axis defined as lead 1 positive and AVF lead positive. Left axis deviation defines lead 1 positive and AVF lead negative
• Right axis deviation defines as lead 1 negative and AVF lead positive. Extreme right axis deviation defined as lead 1 negative and AVF negative

HYPERTROPHY

• Hypertrophy is defined as enlargement of the tissue or organ
• Atrial enlargement includes right atrial enlargement (RAE) and left atrial enlargement (LAE). Right atrial enlargement is peaked P-wave, more than 2.5 mm in any lead (best seen in II, III, V3 and V1). Left atrial enlargement is P-wave duration is more than 0.08 seconds, may have plateau or notched counter. Terminal and deep invasion of the P wave is V2 or V1
• Right ventricular hypertrophy shows dominant R in V1 or V2 essential
• Dominant S in I, AVL, V5 or V6 and inverted T and depressed ST in leads with dominant R
• Left ventricular hypertrophy shows large R wave in lead I, AVL, V5 and V6 and more than 30 mm. inverted T and depressed ST in leads with a large R-wave. Essential criteria for left ventricular hypertrophy is S in V1 or V2 + R in V5 or V6 = /35 MM

ELECTROLYTE DISTURBANCE IN ECG

• Normal serum potassium (K) value is 3.5 to 5.0 mEq/L. extremely serious problem occurs if potassium level less than 2.5 mEq/L or more than 7.0 mEq/L
• If the potassium level less than 5.0 mEq/L called hyperkalemia causes wide flat P wave, prolonged PR interval, decreased R-wave, widen QRS complex and peaked narrow T-wave in the ECG
• Serum potassium level less than 3.5 mEq/L is called hyperkalemia causes prolonged P wave, depressed ST segment and large U-wave is seen in ECG
• Serum calcium level is 8.5 – 10.5 mg/dL. If the serum calcium level less than 8.5 mg/dL is called hypocalcemia. Calcium level more than 10.5 mg/dL called hypercalcemia. Hypercalcemia shows increased QT interval and hypocalcemia shows decreased QT interval in the ECG

MYOCARDIAL INFARCTION

• Anterioseptal (anterior) myocardial infarction causes ECG changes are abnormal Q wave in lead 1, AVL and V1-V3. Reciprocal changes are depressed ST segment in lead II, III, and AVF
• Anteriolateral (lateral) myocardial infarction causes abnormal Q-wave in lead 1, AVL and V5-V6. Reciprocal changes are depressed ST in lead II, III and AVF
• Inferior myocardial infarction causes abnormal Q wave in lead II, III and AVF
• Posterior myocardial infarction causes often large dominant R in lead V1 and V2

12 LEAD ECG

Electrocardiogram Consist of Record from 12 Leads

The three standard bipolar leads (I, II and III), three unipolar limb leads (AVR, AVL, AVF) and six unipolar chest leads (V1-V6)

LEAD PLACEMENT

• Lead I: right arm to left arm
• Lead II: right arm to left leg
• Lead III: left arm to left leg
• AVR: right arm
• AVL: left arm
• AVF: left foot
• V1: 4^th RICS at right sterna border
• V2: 4^th LICS at left sternal border
• V3: midway between V2 and V4
• V4: 5^th LICS at midclavicular line
• V5: 5^th LICS at anterior axillary line
• V6: 5^th LICS at midaxillary line

INDICATIONS FOR 12 LEAD ECG

• Dysrhythmia
• Chest pain
• Myocardial infarction
• Heart rate determination
• Hypertrophy or chamber dilatation
• Preoperative assessment
• Pericarditis
• Effects of systemic disease on heart
• Effects of electrolyte disturbances

CAUSE OF ABNORMAL ECG PATTERN

• Skeletal muscle activity or movement of the patient
• Loose electrodes
• Damaged or broken wires
• Improper connections
• Improper placement of electrodes
• Electrical interferences

PREPARATION OF THE PATIENT

• There is no way special preparation for the investigation
• Explain the procedure to the patient and relatives that the seemingly complex apparatus will do no harm but will give information on the action of the heart
• There should not be any ornaments during ECG on the body or the leads should not come in contact with the ornaments
• Apply jelly to the skin where electrode is to be attached to have a good contact between the skin and the electrode
• Give flat and relaxed position to the patient because any movements or muscular twitching recorded by the machine may alter the tracings
• Clean the jelly off the electrode sites before leaving the patient

There are specific positions for the placement of the chest leads. The improper placement of the chest leads can distort the tracing and alter the diagnosis

PREPROCEDURAL CARE

• Check and arrange the ECG machine, cables, and electrodes and needed articles ready in advance
• Explain the procedure clearly to the patient and family
• Check the doctor’s order for the ECG
• Identify the patient name, age, Id. No. and diagnosis
• Inform the patient not to move during procedure

PROCEDURE

• Position the patient relaxed and flat
• Inform the bystanders to keep away, to prevent them touching the patient during procedure
• Enter the identification data of the patient
• Expose the needed area for connecting electrode
• Stay with the patient till it get over

AFTER CARE

• Clean the patient’s electrode site with gauze or tissue paper
• Ambulate and transfer the patient send the ECG record to doctor for interpretation
• Replace the ECG machine and articles to the proper place
• Record and report in the nurse’s sheet

NURSE’S RESPONSIBILITY

• Nurses working in coronary care unit and intensive care unit should know to operate the ECG machine
• Nurses should able to interpret and identify the dysrhythmia
• Nurses should understand about the dysfunctions and loose connections
• Nurses working in coronary care unit are responsible in ECG interpretation and treating with appropriate life-saving method as per institutional protocol