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Inferior Wall M.I. and Right Bundle Branch Block

These ECGs were taken from a 76 year-old-man who was complaining of chest pressure for 20 minutes.  He had a remote history of coronary artery bypass graft surgery.

This case has several good teaching points, including:

Significant artifact.  The limb leads show artifact which is severe enough to hamper our assessment of the j point location. Every effort should be made to eliminate artifact.  Some measures that might help are:

        *  clean and slightly "rough up" the skin where the electrode will be placed.  A rough wash cloth or gauze pad will work.

        *  shave hair if necessary.

        *  avoid areas of movement if possible.  Precordial electrodes must be placed in specific spots, but limb leads may be placed anywhere on the limb or on the trunk if it is impossible to avoid movement on the limbs.

       *   use fresh electrodes that have been protected from drying out.

Subtle STEMI changes.   This patient has an inferior wall M.I., which was confirmed as a complete occlusion of the right coronary artery in the cath lab.  The ST elevation in Leads II, III, and aVF is subtle, and more difficult to measure because of the artifact.  However, the SHAPE of the ST segments is a giveaway - they are very straight.  A convex-upward shape is normal (see Lead I).  Also, Lead aVL shows typical ST DEPRESSION, as a reciprocal view of the STE in Lead III.  More ST depressions can be seen in Leads V1 through V3, and they end abruptly there.  These localized ST depressions represent a reciprocal view of the posterior (also called lateral) wall, and represent an "extension" of the inferior wall M.I. up the back of the heart.  A V4 Right lead was obtained and shows no measurable ST elevation, but the shape is straight to slightly "frowning", indicating that the right ventricle may soon have STE.  Repeat ECGs should be obtained to watch for more definite ST elevations.

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ECG Basics: Sinus Tachycardia, Peaked T Waves, and Baseline Artifact

This strip offers several good teaching opportunities.  If it were a 12-lead ECG, no doubt it would be a bonanza!  First, there is sinus tachycardia at a rate of about 138 per minute.  The P waves are all alike and regular.  The T waves are tall and narrow, with a sharp peak.  This is often a transient sign of hyperkalemia, and should be investigated with serum electrolyte tests and with a 12-lead ECG.  In addition, the baseline shows a wandering type of artifact.  This is due to the patient's deep breathing, and the fact that the arm electrodes were placed on the chest.  This patient was a diabetic in ketoacidosis with hyperkalemia. 

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This ECG is being offered as a teaching aid, to show how artifact can affect our ability to interpret an ECG, and to encourage our students to be meticulous in obtaining a good-quality tracing whenever possible.  If there are insurmountable obstacles preventing a technically good tracing, the circumstances should be written on the ECG.  Such obstacles could be:  seizures, tremors, vigorous resuscitation efforts underway, or patient not cooperating. 

When an ECG has obvious signs of artifact, the causes of the artifact should be corrected and the ECG repeated.  Teach your students to strive for perfection. Even though we cannot obtain “perfection”, if we settle for sloppiness, it will breed more sloppiness. 

This ECG has some intriguing abnormal signs, but we should wait for a better tracing before attempting a firm interpretation.  We do see abnormal ST segments and T waves in the high lateral leads I and aVL. These, along with the high voltage in aVL, suggest left ventricular hypertrophy with strain.  We would expect to see similar signs in the lateral chest leads, V5 and V6, also.  The second beat on the ECG appears different from the others, and has a P wave.  Even though it is not premature, it could be presumed to have been conducted aberrantly.  The precordial leads show poor R wave progression.  They should all have an RS pattern, with V1 having a small r wave and a large S wave.  The R waves should get more prominent as we move across the chest toward V6, while the s waves become less prominent.  So, V1 should be mostly negatively deflected, and V6 should be nearly all positive, with a gradual transition across the chest leads.  Poor R wave progression can have many causes.  The most preventable one is poor lead placement. 

This ECG offers a chance to illustrate to your students why they should understand how each lead is derived.  Knowing which limb electrodes are used for each limb lead will lead you, in this case, to the faulty electrode, which may simply be loose.  We can see that Lead I is unaffected by the baseline artifact.  Lead I is derived from the left and right arm electrodes.  Lead II is derived from the left leg and the right arm, and Lead III is derived from the left leg and the left arm.  Since Leads II and III are obviously affected by the artifact, which makes the left leg the culprit electrode. 


Dawn's picture

Transcutaneous Pacemaker: Failure to Capture and False QRS Artifact

 When using a transcutaneous pacemaker, it is important to remember that the pacing stimulus can cause an artifact on the ECG.  This artifact is sometimes confused for a QRS complex.  Also, the pacing of the chest wall muscles can be misinterpreted as a pulse.  A “real” QRS complex will have a T wave. 

In this strip, the underlying sinus bradycardia is uninterrupted across the strip.  The rate is very slow – in the 30’s. 

At the beginning of the strip, there are four pacing stimuli, with artifact.  The pacemaker is in fixed mode.  It does not sense the normal QRS that occurs after the second pacing stimulus.  There is failure to sense AND failure to capture.  Apparently, the pacing is stopped, then the pacer is set to “demand” mode.  The pacemaker is sensing the patient’s native beats, but not pacing.  It is likely that the rate and/or the MA, or milliamps, need to be increased to achieve pacing with capture.

 This is a good ECG to illustrate the artifact that is possible with transcutaneous pacing, and remind your students not to assume the patient is being paced.  The patient’s clinical signs (skin perfusion, blood pressure, mentation) should be used to determine whether the rate is adequate.


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Normal Sinus Rhythm With PACs Misdiagnosed As Atrial Fibrillation

This patient was diagnosed by the rescue crew as having atrial fibrillation, based on the fact that they thought the rhythm was irregular, and they could not see P waves.  They also noted a wavy baseline, and considered it to be fibrillatory waves.  In reality, the underlying rhythm is regular, with some PACs (regularly irregular). The P waves are small and hard to see in the baseline artifact.  We have marked the P waves in Lead I with small dots.  

It pays to look at multiple leads, reduce artifact as much as possible, and look at the strip for evidence of an underlying rhythm.  

It is not shown here, but the ECG machine is often able to show that the P waves are present by giving a PR interval and P wave axis in the diagnostics.

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Left Bundle Branch Block and Artifact

This ECG offers several teaching opportunities.  First, it is an example of left bundle branch block (LBBB).  It was obtained from a 53-year-old man who was undergoing a cardiac cath for chest pain.  Unfortunately, we do not have access to his past medical history or the results of his cath.  The ECG criteria for a diagnosis of LBBB are:  1) wide QRS complex; 2) supraventricular rhythm; 3) negative QRS in V1 and positive QRS in V6 and Lead I.  This ECG shows normal sinus rhythm at a rate of 88 bpm and a wide QRS at 158 ms (.158 seconds).  The QRS in V1 is negatively deflected and in V6 and Lead I it is positive.

In LBBB, as with any condition that significantly widens the QRS, there will be ST-T changes.  The ST segment will deviate in the opposite direction of the QRS.  In other words, there will be ST elevation in leads with negative QRS complexes and ST depression in leads with positive QRS complexes.  LBBB causes significant difficulty for those trying to diagnose acute ST elevation using ECG alone.  Excessive ST elevation in a lead where elevation is expected OR ST elevation in a lead where depression is expected should be considered to be abnormal.  At this point, you may find it useful to review Sgarbossa's Criteria regarding determining the presence of acute M.I. in the presence of LBBB.

LBBB can be a serious functonal problem for the patient, as the slow ventricular conduction that causes the wide QRS results in less-than-optimal cardiac output.  This associates LBBB with congestive heart failure, both as a cause of CHF and a result of CHF.  Many people with LBBB and CHF can be helped by cardiac resynchronization therapy - pacing both ventricles synchronously to narrow the QRS and improve cardiac output.  For an excellent article on cardiac pacing in general and CRT (page 2299), go to the 2013 European Society of Cardiology Guidelines as reported by the European Heart Journal, (2013) 34, 2281–2329 doi:10.1093/eurheartj/eht150

Dawn's picture

Inferior Wall MI With Artifact

This ECG is taken from a 66-year-old man who presented to the Emergency Dept. with a complaint of chest pain.  The ECG shows clear signs of acute inferior wall MI:  ST segment elevation in Leads II, III, and aVF and reciprocal ST depression in Leads I and aVL.  In addition, there are reciprocal ST depressions in Leads V1, V2, and V3.  These indicate that the MI extends up the inferior wall into the area called by most clinicians the posterior wall.  When the injured area extends high enough from the inferior wall, it becomes visible to the anterior-septal leads as ST depression.  There is also a small ST elevation in Leads V5 and V6, the low lateral wall, indicating a common blood supply for the inferior and low lateral walls (usually the right coronary artery).  All of these findings make this a rather "typical" inferior wall MI.

Unfortunately, this ECG also has a significant amount of artifact.  The second, sixth, and tenth "beats"  appear to be  premature beats in Leads I and II.  However, it is important to remember that the four channels on this ECG are run simultaneously.  That is, any complex of significant voltage should show up four times.  The "premature" beats do not appear in Lead III, and do not affect the timing of the appearance of the next beat at all.  They also appear during moments of baseline disruption, indicating that they are not heartbeats, but simply artifact.

Why is this important?  Artifact makes the ECG hard to interpret accurately.  The ECG machine even had a difficult time, completely ignoring obvious P waves, and calling the rhythm "atrial fibrillation".  Every effort should be made to obtain the cleanest, most artifact-free ECG possible.

Additional note:  it can be very informative to do a right-sided ECG on an IWMI patient, or at least a V4Rt.  In fact, it is a protocol requirement in many EMS agencies.  Right ventricular infarction can change the hemodynamics of your patient, causing a need for fluid resuscitation. In fact, a drop in BP, such as that caused by nitroglycerin, can cause circulatory collapse.  Ntg should be given cautiously to RVMI patients.  Fortunately, IV fluids will seldom cause left heart overload in these patients.  A look at the right ventricle with V4Rt can be very helpful in deciding treatment options.

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ECG Basics: Baseline Artifact

This rhythm strip shows normal sinus rhythm, slightly on the fast side of normal at 95 bpm.  The baseline undulates up and down with the movements of the patient's chest as she breathes.  One way to correct this problem on a monitor strip is to move the limb electrodes away from the chest and onto the limbs.

Dawn's picture

Artifact on an ECG With Inferior, Posterior, Lateral M.I.

If you are an ECG instructor, it is important that you address the subject of artifact on the ECG.  Artifact has many causes, and it is important eliminate it whenever possible.  We should strive for the "cleanest" ECG possible.  As you can see in this example, the presence of artifact has caused the machine's computer rhythm interpretation to be incorrect.  The noisy baseline has caused the computer to call this rhythm "atrial fibrillation", but we clearly see P waves in all leads, especially in Lead II.  We recognize these P waves as authentic because they are regular, they  all look alike, and they have the same relationship to the QRS complexes each cycle (PR interval is the same).  

The patient is suffering a very large M.I., showing as ST segment elevation in Leads II, III, aVF, with slight elevation in V5 and V6.  In addition, Leads V1 through V3 have definite  ST depression, indicating extension of the inferior wall injury up the posterior wall of the heart.  There has been quite a bit of discussion lately in the literature about whether to call this a "posterior" M.I, or "high lateral", or just "inferior".  Semantics aside, the involvement of so many leads tells us that this  is a large M.I.  The patient was in the Emergency Dept. complaining of chest pain.

It is fortunate that the artifact did not affect our ability to see the ST elevation, but it could have.  And, of course, we would not want to treat this patient's "atrial fib" based on the machine interpretation.  But, it is always prudent to try to get rid of artifact.  In this example, Lead III has no artifact, so it could be assumed that the right arm electrode is the culprit, as Lead III does not utilize the RA electrode, and the other leads do.  

Troubleshoot for the cause of the artifact, and then retake the ECG.  Some common causes of baseline  artifact of this nature include:  patient movement, loose electrode, dried electrode, something touching the electrode, faulty or broken lead wire, and poor skin contact due to substances on the skin.  The electrodes should be fresh from the package, and applied to skin that is clean and dry.  The patient should be encouraged to relax and hold still (not so easy for a patient in distress).  Others at the bedside should avoid touching or manipulating the limbs of the patient during acquisition of the ECG data.  This only takes about 10 seconds.  I have seen artifact many times when a patient's blood was being drawn during the ECG, and the patient was squeezing his fist for the phlebotomist.

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ECG Basics: 60-cycle Artifact

Here is a good example of 60-cycle interference artifact on a sinus rhythm strip.  The artifact is caused by electrical interference from a nearby electrical appliance. Modern monitors are able to filter interference out, but it is still occasionally seen.  Even though we can still discern P waves in this strip, and we can see that the rhythm is irregular, possibly sinus arrhythmia, the artifact prevents us from accurately evaluating the strip.  Every effort should be made to identify the offending device.  In "ECG Basics", we attempt to stay "basic", but if any of our Gurus would like to comment on this in a more technical fashion, it is welcome.

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