A 12-lead electrocardiogram

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Dr Abdul-Monim BatihaDr Abdul-Monim Batiha

Dr Ibrahim BashayrehDr Ibrahim Bashayreh

A 12-lead electrocardiogram (ECG)

ECG is a graphic record of electric currents that are generated by the heart muscles.Electrical impulses are picked up by the surface electrode which are placed at various points on the body and connect the ECG machine to the body.

ObjectivesObjectives

To diagnose the presence of MI.To diagnose the presence of

cardiac dysrrhythmias. To diagnose the presence of

cardiac enlargement and size of cardiac champers.

To detect the electrolyte abnormalities especially K and Ca.

To evaluate the effect of To evaluate the effect of therapeutic interventions on therapeutic interventions on the heart ( e.g. drugs, fluid, the heart ( e.g. drugs, fluid, and mechanical support) and mechanical support)

The 12-lead ECG provides “views” of cardiac electrical activity from 12 different vantage points on the body surface.

ASSESSMENT1. Assess age, gender, and current

medication history for any medications with possible cardiac or hemodynamic effects. Gather other data that may be required by unit/institution protocol (height, weight, recent blood pressure, operator identification).

A 15-lead ECG adds 3 additional chest leads across the right precordium and

is a valuable tool for the early diagnosis of right ventricular and posterior left ventricular infarction. The 18-lead ECG adds 3 posterior leads to the 15-lead ECG and is very useful for early detection of myocardial ischemia and injury

Determine that the client is able to tolerate a supine position and that adequate exposure of chest and limbs is possible for electrode placement. Correct sitting of electrodes is enhanced by comfortable, stable position.

Determine presence of neck, arm, jaw, or other pain with possible cardiac origin. Chest or other pain may provide additional information useful in serial comparison of ECGs.

Assess client need for information about the procedure purpose and requirements and ability to cooperate: that client should lie still and refrain from talking, electrode attachment, procedure lasts only a few minutes and is painless. Anxiety may be relieved by simple explanation of intent, duration, and purpose.

Equipment Needed

• Twelve-lead ECG machine with charged battery,

cables and leads, graph paper• Disposable electrodes (12)• Electrode paste or gel• Alcohol wipes• Pillows• Sheet or drape• Towel and washcloth• Disposable razor

Each of the 12 leads represents a particular Each of the 12 leads represents a particular orientation in space, as indicated below (RA orientation in space, as indicated below (RA = right arm; LA = left arm, LF = left foot):= right arm; LA = left arm, LF = left foot):

   Bipolar limb leads (frontal plane):Bipolar limb leads (frontal plane):

   Lead I: RA (-) to LA (+) (Right Left, or Lead I: RA (-) to LA (+) (Right Left, or lateral)lateral)

 Lead II: RA (-) to LF (+) (Superior Inferior)  Lead II: RA (-) to LF (+) (Superior Inferior)

 Lead III: LA (-) to LF (+) (Superior Inferior)  Lead III: LA (-) to LF (+) (Superior Inferior)

Continuous Electrocardiographic

Monitoring

Continuous ECG monitoring is standard for patients who are at high risk for dysrhythmias.

Two continuous ECG monitoring techniques

hardwire monitoring, found in critical care units and specialty step-down units, and

telemetry, found in specialty step-down units and general nursing care units.

Patients who are receiving continuous ECG monitoring need to be informed of its purpose and cautioned that this monitoring method will not detect symptoms such as dyspnea or chest pain. Therefore, patients need to be advised to report symptoms to the nurse whenever they occur.

HARDWIRE CARDIAC MONITORING

The patient’s ECG can be continuously observed for dysrhythmias and conduction disorders on an oscilloscope at the bedside or at a central monitoring station by a hardwire monitoring system.

Objectives of cardiac monitor Objectives of cardiac monitor

• Monitor more than one lead simultaneously

• Monitor ST segments (ST-segment depression is a marker of myocardial ischemia; ST-segment elevation provides evidence of an evolving MI)

• Provide graded visual and audible alarms (based on priority, asystole would be highest)

• Computerize rhythm monitoring (dysrhythmias are interpreted and stored in memory)

• Print a rhythm strip• Record a 12-lead ECG

Two leads commonly used for continuous monitoring are leads II and V1 or a modification of V1 Lead II provides the best visualization of atrial depolarization (represented by the P wave). Leads V1 and II best visualize the ventricle responsible for ectopic or abnormal ventricular beats.

Following the guidelines for electrode placement will ensure good conduction and a clear picture of the patient’s rhythm on the monitor:

•

Clean the skin surface with soap and water and dry well (or as recommended by the manufacturer) before applying the electrodes. If the patient has much hair where the electrodes need to be placed, shave or clip the hair.

Apply a small amount of benzoin to the skin if the patient is diaphoretic (sweaty) and the electrodes do not adhere well.

PULSE OXIMETRY

Is a noninvasive method of continuously monitoring the oxygen saturation of hemoglobin (SpO2 or SaO2). Although pulse oximetry does not replace arterial blood gas measurement, it is an effective tool to monitor for subtle or sudden changes in oxygen saturation.

It is used in all settings where oxygen saturation monitoring is needed, such as the home, clinics, ambulatory surgical settings, and hospitals.

It is used in all settings where oxygen saturation monitoring is needed, such as the home, clinics, ambulatory surgical settings, and hospitals.

A probe or sensor is attached to the fingertip, forehead, earlobe, or bridge of the nose. The sensor detects changes in oxygen saturation levels by monitoring light signals generated by the oximeter and reflected by blood pulsing through the tissue at the probe.

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Physiologic Limitations.

Elevated levels of abnormal hemoglobins,

Presence of vascular dyes, Poor tissue perfusion. The pulse

oximeter cannot differentiate between normal and abnormal hemoglobin.

Elevated levels of abnormal hemoglobin falsely elevate the Spo2.

Vascular dyes such as methylene blue, indigo also interfere with pulse oximetry and can lead to falsely low readings.

Poor tissue perfusion to the area with the probe leads to loss of pulsatile flow and signal failure.

Technical Limitations.

Technical limitations include Bright lights, Excessive motion, Incorrect placement of the probe.

Bright lights may interfere with the photodetector and cause inaccurate results. The probe must be covered to limit optical interference.

Excessive motion can mimic arterial pulsations and can lead to false readings. Incorrect placement of the probe can lead to inaccurate results, because part of the light can reach the photodetector without having passed through blood (optical shunting).

Interventions to limit these problems include

Using the proper probe in the appropriate spot (e.g., not using a finger probe on the ear),

Applying the probe according to the directions, and ensuring that the area being monitored has adequate perfusion.

Equipment

Pulse oximeterSensor (permanent or disposable)Alcohol wipe(s)Nail polish remover, if indicated

AssessmentSigns and symptoms of hypoxemia

(restlessness; confusion; dusky skin, nailbeds, or mucous membranes)

Quality of pulse and capillary refill proximal to potential sensor application site

Respiratory rate and characterPrevious pulse oximetry readingsAmount and type of oxygen

administration, if applicableArterial blood gases, if available

Capnography

Is the measurement of exhaled carbon dioxide gas and can be used to monitor a patient's ventilatory status. A capnograph is also known as an end-tidal CO2 monitor, because the CO2 is measured near the end of the exhalation.

Most often, the gas sample is analyzed through infrared gas analysis. Frequently the CO2 is measured via the exhalation port of the ventilator tubing; as the gas passes through the sensor, the data are transferred to the display unit. A display unit produces a waveform, called a capnogram

and a numeric recording approximating the Paco2.

The ability of the capnograph to approximate arterial Paco2 is altered with abnormal cardiopulmonary function

Clinical application ofcapnography

can provide information in a number of areas including:

Estimation of Paco2 levels, Assessment of dead space

(increased V/Q),Assessment of pulmonary blood flow,

and endotracheal tube placement.

Normally alveolar and arterial CO2 concentrations are equal in the presence of normal ventilation/perfusion relationships. In a patient who is hemodynamically stable, the end-tidal CO2 (Petco2) can be used to estimate the Paco2, with the Petco2 levels 1 to 5 mm Hg less than Paco2 levels.The practitioner must determine first that a normal V/Q relationship exists before correlation of the Petco2 and the Paco2 can be assumed.

Assessment of changes in physiologic dead space can be carried out with end-tidal CO2 monitoring, based on the degree of difference between the Paco2 and the Petco2. As the severity of pulmonary impairment increases, so does the disparity between the Paco2 and the Petco2, as indicated by an increased gradient.

A gradient of greater than 5 mm Hg can be seen with underperfused alveolar-capillary units (dead space–producing situations) and nonperfused alveolar-capillary units (alveolar dead space). Increased dead space ventilation is a result of decreased pulmonary blood flow or cardiac output and lung disease. This leads to an abnormality in the transfer of CO2 from the blood to the lung.

The result is a Petco2 level that is lower than the Paco2 because of the mixing of carbon dioxide between perfused and nonperfused units. The end result is an increased or widened Paco2-to-Petco2 gradient.

The noninvasive measurement of Petco2

Allows for :The assessment of adequacy of

cardiopulmonary resuscitation and endotracheal tube placement.

Decreased pulmonary blood flow is associated with lower Petco2 values, reflected clinically by decreased cardiac output, as in the case of cardiopulmonary resuscitation.

During endotracheal intubation, a low Petco2 reading would indicate that the tube is positioned in the stomach, because the amount of carbon dioxide in the esophagus is expected to be low.

Sublingual Capnometry

Sublingual carbon dioxide (PSLco2) measurement is a new noninvasive technology available for monitoring patients at risk for hypoperfusion. Unrelieved hypoperfusion has been closely linked with development of multisystem organ dysfunction syndrome (MODS).