2A tracing of the heart’s electrical activity ElectrocardiogramA tracing of the heart’s electrical activity
3ElectrocardiographDetects heart’s electrical activity through electrodes positioned on patient’s skinInstructional point:Lead wires transfer electrical activity back to ECG machine where it is displayed on an oscilloscope and/or printed onto graph paper.I
4ECG PaperGrid layout on ECG paper consists of horizontal and vertical lines.Allows quick determination of duration and amplitude of waveforms, intervals and segments.I
5ECG PaperEach small square = sec in duration and 0.1 mV in amplitudeFive small squares = One large box and 0.20 seconds in durationHorizontal measurements determine heart rateInstructional point:Vertical markings on top or bottom of ECG paper can be used to quickly approximate the heart rate.I
6Isoelectric Line Flat line that occurs: When no electrical activity is occurringWhen impulses are too weak to be detectedUsed as a baseline to identify changing electrical movement
7P Wave Produced by: Waveform is upright and round initiation of impulse in SA nodedepolarization of RA and LAImpulse passing through AV junctionWaveform is upright and round
8PR SegmentFlat (isoelectric) line seen as impulse travels through His-Purkinje system
9QRS Complex Follows PR segment and consists of: Q wave First negative deflection following PR segmentR waveFirst positive deflection following Q wave or PR segmentS waveFirst negative deflection that extends below the baseline following the R waveInstructional points:The S wave begins at the point where the negative deflection of the R wave reaches the baseline.I
10ST Segment and T Wave ST segment is flat line that follows QRS complex T wave is larger, slightly asymmetrical waveform that follows ST segmentInstructional point:The J point is the site where the S wave connects to the ST segment.I
11QT Interval The distance from onset of QRS complex until end of T wave Measures time of ventricular depolarization and repolarizationHas normal duration of 0.36 to 0.44 secondsInstructional points:The QT interval shouldn’t be greater than half the distance between consecutive R waves when the rhythm is regular.It varies according to age, sex, and heart rate, the faster the heart rate the shorter the QT interval.I
12Typical ECGUpright, round P waves occurring at regular intervals at a rate of 60 to 100 beats per minutePR interval of normal duration (0.12 to 0.20 seconds) followed by a QRS complex of normal upright contour, duration (0.06 to 0.12 seconds) and configurationFlat ST segment followed by an upright, slightly asymmetrical T wave
13Calibration or Registration Mark Helps ensure ECG machine is properly calibratedServes as reference point on ECG tracingInstructional points:The calibration or registration mark should be included on every ECG tracing.Some ECG machines create this mark automatically while with others it must be placed manually.I
14ArtifactMarkings on ECG tracing that are not a product of heart’s electrical activityPatient movement is among its many causesCan mimic life-threatening dysrhythmiasInstructional point:Emphasize the need to assess the patient whenever any sort of chaotic electrical activity is seen on ECG.I
15ECG Machines A variety of machines are available Some monitor from one to five different leadsOthers are capable of monitoring up to twelve or more leads simultaneouslyInstructional points:ECG machines used to provide continuous cardiac monitoring are often referred to as an ECG monitor.Many are equipped with a defibrillator and pacemaker.I
16ECG Leads Each lead provides a different view of the heart: Electrodes are placed on chest, arms and legsSites vary depending on which view of the heart's electrical activity is being assessedInstructional points:A lead is the view between one positive and one negative pole.Information obtained through just one lead is limited while multiple leads can help identify needed information.I
17ECG LeadsDirection an ECG waveform takes depends on whether electrical currents are traveling toward or away from a positive electrodeInstructional note:A biphasic waveform is composed of both positive and negative deflections.I
18ECG Leads Planes provide a cross-sectional view of heart Frontal plane Horizontal planeInstructional point:Frontal plane is a vertical cut through middle of heart while horizontal plane is a transverse cut through middle of heart.I
19Limb Leads View the frontal plane Include leads I, II, III, aVR, aVL and aVFProvide inferior, superior, and lateral views of heart
20Precordial LeadsView horizontal plane and include leads V1, V2, V3, V4, V5, and V6Provide inferior, superior, and lateral views of heart
21Unipolar LeadsUse one positive electrode and a reference point which is calculated by the ECG machine
22Uses for Different Leads A given lead may be used to highlight:A specific part of ECG complexElectrical events of a specific cardiac cycleConditions such as an enlargement of heart muscle or presence of ischemia, injury and infarctionInstructional points:Leads I, II, III or MCL leads are typically used for continuous cardiac monitoring to identify the presence of and/or developing cardiac dysrhythmias).12 leads are used to obtain specific diagnostic information.I
23Bipolar LeadsRecord difference in electrical potential between a positive and negative electrodeUses a third electrode called a groundInclude leads I, II and IIIInstructional point:Axes of these three bipolar leads forms a triangle around the heart referred to as Einthoven’s triangle.I
24Limb Leads - Lead IPositive electrode - left arm (or under left clavicle)Negative electrode - right arm (or below right clavicle)Ground electrode - left leg (or left side of chest in midclavicular line just beneath last rib)Waveforms are positive
25Limb Leads - Lead IIPositive electrode - left leg (or on left side of chest in midclavicular line just beneath last rib)Negative electrode - right arm (or below right clavicle)Ground electrode - left arm (or below left clavicle)Waveforms are positive
26Limb Leads - Lead IIIPositive electrode - left leg (or left side of the chest in midclavicular line just beneath last rib)Negative electrode - left arm (or below left clavicle)Ground electrode - right arm (or below right clavicle)Waveforms are positive or biphasic
27Limb Leads - Augmented Leads Includes aVR, aVL and aVFUnipolarEnhanced by ECG machine because waveforms produced by these leads are normally smallInstructional point:The ECG machine augments these leads by 50% to make them easier to seeI
28Limb Leads - Lead aVR Positive electrode placed on right arm Waveforms have negative deflection
29Limb Leads - Lead aVL Positive electrode placed on left arm Waveforms have positive deflection
30Limb Leads - Lead aVF Positive electrode located on left leg Waveforms have a positive deflection
31Precordial Leads Includes leads V1, V2, V3, V4, V5 and V6 Positioned in order across the chestUnipolarOpposing pole is center of heart as calculated by ECGInstructional point:Provide information about horizontal plane of heart.I
32Modified Chest Leads (MCL) MCL1 and MCL6 provide continuous cardiac monitoringPlace positive electrode in same position as precordial leads V1 or V6Instructional point:Modified chest leads are employed primarily to detect dysrhythmias.I
33SummaryElectrodes placed on patient’s skin detect heart’s electrical activity.Graphic record or tracing is called an electrocardiogram.Abnormalities in cardiac rate and/or rhythm are called dysrhythmias.
34SummaryECG paper consists of horizontal and vertical lines that form a grid.Horizontal measurements used to determine heart rate and duration of various waveforms, segments and intervals.Vertically on ECG paper, distance between lines, or boxes, represents amplitude in millimeters (mm) or electrical voltage in millivolts (mV).
35SummaryConduction of electrical impulse through the heart can be seen on ECG as P wave, PR interval, QRS complex, ST segment and T wave.Artifact is markings on ECG tracing that have no relationship to electrical activity of the heart.
36Summary Each lead provides a different view of heart. Impulses traveling toward a positive electrode are recorded on ECG as upward deflections.Impulses traveling away from a positive electrode or toward a negative electrode are recorded as downward deflections.
37SummaryLimb leads are produced by placing electrodes on right arm (RA), left arm (LA) and left leg (LL).Include leads I, II, III, augmented vector right (aVR), augmented vector left (aVL) and augmented vector foot (aVF).Precordial leads include leads V1, V2, V3, V4, V5, and V6.