43
CHAPTER
Electrocardiogram:
Pitfalls in Diagnosis and Artifacts
Amit Vora, Samhita Kulkarni
INTRODUCTION
Electrocardiogram (ECG) is the most important test to diagnose
various cardiac and medical disorders, in acute or long-standing
illnesses. It is a very cheap diagnostic tool, readily and universally
available. Accurate ECG interpretation results in prompt
diagnosis and directs appropriate treatment, saving many lives.
However wrong ECG diagnosis results not only in failure to
recognize a potentially life-threatening disease, but may also lead
to unnecessary invasive or expensive treatment, which in itself
may pose serious risk to the patient. Not uncommonly coronary
angiograms, implantable defibrillators, etc. are advised due to
misinterpretation of the ECG. The pitfalls in ECG diagnosis is
either due to a normal ECG in episodic problems like paroxysmal
supraventricular tachycardia (SVT) and during early evolution of
illness like acute coronary syndrome; or an abnormally looking
ECG in a normal individual like early repolarization, etc. Another
important reason of erroneous ECG diagnosis is artifacts. An ECG
artifact is nothing but distortion of the actual electric signals from
the heart. It may be due to human or mechanical errors. Loose
leads, cable artifacts and wrong ECG lead placement are some
of the common causes. ECG artifact can lead to wrong diagnosis
of arrhythmias, ischemia, etc. Understanding the pitfalls in ECG
diagnosis and identifying ECG artifacts is extremely essential to
avoid wrong treatment.
ELECTROCARDIOGRAM:
PITFALLS IN DIAGNOSIS
The pitfalls in ECG diagnosis can be summarized as apparently
normal ECG in pathological conditions (Table 1) and abnormal
ECG in physiological conditions (Box 1).
BOX 1: Abnormal ECG pattern in normal hearts
••
••
••
••
••
Early repolarization
Juvenile T wave changes
Precordial T wave inversion
Left ventricular hypertrophy pattern: thin built
Poor progression of R wave in precordial leads: obesity,
dextrocardia, emphysema
Abbreviation: ECG, electrocardiogram.
TABLE 1: Normal ECG in pathological conditions
Paroxysmal arrhythmias:
Fluctuant/intermittent
syndromes:
Coronary artery disease:
Cardiomyopathies:
••
••
••
••
••
••
••
••
••
••
••
••
Paroxysmal SVT
Idiopathic VT
Paroxysmal AV block
CPVT/fibrillation
Brugada syndrome
LQTS
Intermittent preexcitation
Acute coronary syndrome—early ECG
Stable coronary artery disease
Posterior wall MI
Hypertrophic cardiomyopathy
Infiltrative cardiomyopathy
Abbreviations: SVT, supraventricular tachycardia; VT, ventricular tachycardia; AV,
atrioventricular; CPVT, catecholaminergic polymorphic ventricular tachycardia;
LQTS, long QT syndrome; ECG, electrocardiogram; MI, myocardial infarction.
Normal Electrocardiogram in
Pathological Conditions
One of the biggest limitations of an ECG is that it can be completely
normal in paroxysmal condition during periods when the patient
238
SECTION 4: Cardiac Investigation
has no symptoms. In some situations, the first ECG is normal and
serial ECGs are required to evaluate the presence or progression
of the disease. Therefore, ECG can be regarded as a guide to the
diagnosis of relevant cardiac conditions and may not instantly
reveal the pathology. Most importantly the ECG should always be
interpreted taking into consideration the presenting symptoms,
understanding the relevant signs, in conjugation with other tests
and being aware of the potential syndromes.
Chest pain evaluation by ECG is the most common test
required by clinicians. It needs to be emphasized that a normal
ECG does not rule out coronary artery disease. Angina is a
clinical diagnosis and the ECG is often normal when taken at
rest. In the ischemic cascade of acute coronary syndrome, ECG
changes often appear after the onset of chest pain and up to
10% of patients can have a normal ECG at presentation.1,2 At
times a proximal left anterior descending artery occlusion shows
a near normal ECG with upright T waves in precordial leads
during acute chest pain but show deep T inversion in absence
of pain.3 Therefore in acute chest pain, serial ECGs clinch the
diagnosis. Importantly an isolated right ventricular or posterior
wall infarction can be missed in the standard 12 lead ECG and
accurate diagnosis requires additional right precordial leads or
posterior leads. Needless to state that patients with stable triple
vessel disease may have a normal ECG.
Another clinical scenario in which the baseline ECG would
not always be helpful is in the evaluation of arrhythmias.
Episodes of SVT, atrial fibrillation and ventricular tachycardia
(VT)/ventricular fibrillation (VF) can be paroxysmal and the
ECG will be normal in absence of palpitations or syncope. It is
very important to consider the presence of these arrhythmias
to work-up these patients appropriately. Often a Holter, event
recorder, stress test or an electrophysiology study is required to
diagnose these paroxysmal arrhythmias. It is not uncommon
to have adolescent children complaint of intermittent, abrupt
palpitations and their ECG or clinical evaluation is normal and
they are wrongly considered as anxiety related. There are some
reports of patients being on antidepressants. Most paroxysmal
SVT and idiopathic VT are benign, but some of the tachycardia’s
(catecholaminergic polymorphic VT) can be malignant and
cause sudden cardiac death (SCD) in the young.4
Similarly in the evaluation of syncope, it is difficult to
diagnose paroxysmal atrioventricular (AV) blocks or intermittent
sinus pauses on a single ECG. Also conditions like vasovagal
and carotid sinus hypersensitivity will show bradycardia only
at the time of the episode and at other times will be completely
normal. Inherited arrhythmias like long QT syndrome (LQTS)
and Brugada syndrome are often known to show the classic ECG
change only intermittently.5
Dyspnea is a common manifestation of many cardiac
conditions. ECG is useful in the evaluation of cardiomyopathies,
valvular heart disease, etc. However often the ECG is normal
or shows only subtle abnormalities that can be easily missed.
Clinical examination followed by echocardiography help in
accurate diagnosis. The classic ECG changes of acute pulmonary
embolism S1Q3T3 pattern and right ventricular strain are often
not obvious and there may only be sinus tachycardia, hence a
high index of suspicion is required for appropriate diagnosis.
Abnormal Electrocardiogram Pattern in Normal Hearts
Early repolarization is one of the most common ECG variants. It
is manifested as elevated J point with notching of downstroke of
QRS complex, especially in right and mid-precordial leads. This is
commonly seen in young adults. Although historically regarded
as a benign condition, some recent studies have implicated early
repolarization rarely to be associated with VT/VF and SCD.6
T waves can be inverted in right precordial leads in normal
persons. The juvenile T wave pattern consists of inverted T waves
in all precordial leads, which gradually becomes upright. Persistent
juvenile pattern occurs in 1–3% of individuals. Some cases with
early repolarization have biphasic T inversion with ST segment
elevation. When no cause for T wave changes is identified, often
they are termed as idiopathic global T wave inversion.7
Q waves in the absence of coronary artery disease can
be because of various nonischemic causes (Box 2); the most
common being improper lead placement resulting in poor “R”
progression and “QS” pattern. Pneumothorax, dextrocardia and
pectus excavatum also lead to poor R progression in precordial
leads.
BOX 2: Q waves in absence of MI
••
••
••
••
••
••
••
Physiological
Preexcitation
Left ventricular hypertrophy/hypertrophic cardiomyopathy
Obesity, pneumothorax, dextrocardia, etc.
LBBB
Infiltrative cardiomyopathy
Pulmonary embolism
Abbreviations: MI, myocardial infarction; LBBB, left bundle-branch block.
Misleading Electrocardiogram Diagnosis
Left bundle-branch block (LBBB) is associated with QS pattern
in right to mid-precordial leads and occasionally in II, III or
aVF along with ST elevation and this confuses the diagnosis of
additional myocardial infarction (MI). Sgarbossa8 criteria should
be applied to identify acute and old MI in patients with LBBB for
an accurate diagnosis. ST elevation of more than 5 mm in limb
leads and more than 5 mm in precordial leads where there is a QS
pattern (discordant leads), favor acute MI. In concordant leads
(I, aVL, V5 and V6) where there is an R wave, ST depression and
T wave inversion is expected with LBBB; however even a minor
ST elevation of 1 mm in these leads is diagnostic of acute MI.
Remote infarction in LBBB is to be expected when there is a Q
wave in leads I, aVL, V5 and V6 or a R wave in leads V1.
In ECG with Wolf-Parkinson-White pattern, the negative delta
wavescan mimic Q wave of MI. Other causes of a pseudoinfarct
pattern on ECG include hypertrophic cardiomyopathy,
amyloidosis, tumor infiltration, myocarditis, pulmonary
embolism and rarely hyperkalemia.
Similarly, ST segment depression, a marker of subendocardial
ischemia can be seen in nonischemic causes like digitalis toxicity,
ventricular hypertrophy, hypokalemia and hyperventilation.
Deep T wave inversion can be seen in noncardiac causes like
intracranial hemorrhage and raised intracranial tension.
CHAPTER 43: Electrocardiogram: Pitfalls in Diagnosis and Artifacts
WRONG LEAD PLACEMENT
Misplacement of ECG electrodes leads to a confusion in absence
of any pathology. However this can be easily recognized by a
careful review of the ECG or comparison with previous ECGs. The
most important clue is of course a disparity between the clinical
scenario and the ECG changes. The wrong lead placement can be
an interchange between the precordial leads or the limb leads.
Limb Electrode Misconnection
The most common is a right to left interchange, which causes a
characteristic ECG pattern:
•• Inverted P-QRS-T waves in lead I leading to extreme axis
deviation.
•• Normal appearing P-QRS-T in aVR
•• QRS vector in lead I does not match that of V6.
Arm/Leg Lead Reversal
Arm/leg lead reversal is usually confined to the same side, rarely
even the opposite arm and leg leads are interchanged. Reversal
of the right arm/right leg electrodes will lead to a near flat line
in lead II and a right leg/left arm reversal will lead to a flat line
in lead III.
The left arm/left leg reversal is difficult to diagnose in the
absence of a previous ECG for comparison. However the key
findings in such a wrong lead placement9 are:
•• Abnormal aVR appearance (upright P-QRS-T)
•• Lead II becomes I
•• aVF becomes aVL
•• Reverse polarity in lead III.
Limb lead reversal causes significant confusion in
pathological situation like acute MI. The ECG in Figure 1A, is
classic of inferior wall MI, however a later ECG with left arm and
left leg lead reversal suggests a lateral wall MI (Fig. 1B).
Precordial lead misplacement: Fairly common in occurrence,
more so with obesity and feminine anatomy. Misplacement of
precordial leads may result in a pseudoinfarct pattern. Often a
new T wave changes and vastly different R/S ratio from baseline
are recorded in absence of infarction. Precordial lead reversal
can be determined by lack of a smooth R/S transition from rightsided (V1,2,3) leads to left-sided (V4,5,6) leads.
A
B
Figs 1A and B: (A) A middle aged gentleman presenting with acute inferior wall myocardial infarction (MI); (B) Same patient in Figure 1A,
with reversal of left arm and left leg lead suggesting lateral wall MI
239
240
SECTION 4: Cardiac Investigation
ELECTROCARDIOGRAM
ARTIFACTS
Electrocardiogram artifacts can be caused by electrical
interference recorded from sources other than signals from the
heart. Artifacts are often seen in ECG cardioscope and Holter
monitoring. Sources of ECG artifact can be physiological or
nonphysiological. Technical issues include recording the ECG
with nonstandard high and low pass filter settings.
Physiological
Electromyographic signals: From muscles other than heart
muscle, appearing on the monitor as narrow, rapid spikes
associated with muscle movement. These can be avoided by
appropriate electronic filtering. In elderly people, limb tremors
can make the ECG appear like a flutter (Fig. 2) in the limb lead
which has a tremor, however, a simultaneously acquired 12 lead
ECG and comparing other leads would reveal the presence of
normal P waves.
Epidermal signals: Signals caused by voltage generated by
stretching the epidermis, appearing as large baseline shifts when
patient changes position. They are difficult to filter electronically
and their amplitude is greater than the ECG signal.10
Nonphysiological
60 Hz noise: It is also called electrical interference. It produces a
wide, fuzzy baseline and is related to the poor electrode contact
associated with improper skin preparation, evaporated electrode
gel or defective cable/wires. This 60 Hz energy is radiated from
the electric wiring in the room and can be eliminated by filtering
and using an application called common mode rejection.11
Offset potential: It is a voltage stored by the electrode, which can
interfere with the ECG signal. Electrode materials differ in their
ability to store potential, e.g. silver chloride does not allow buildup of offset potential.12 Stainless steel electrodes on the other
hand are plagued with significant build-up of potentials.
Electrode gel: Adequate gel is essential for the efficient
transmission of signals from skin to electrode.
Lead wire/cable: Breakage, poor cable connection or cable
movement can cause significant monitoring problems (Fig. 3).
Electrode impedance: A low impedance (<5,000 Ω) is essential for
transmission of electric signals from skin to electrode. Reasons
for increase in impedance include deficient electrode gel,
inadequate skin preparation.13
Compute Averaging
This is another important source of error in ECG interpretation,
especially in stress test and some of the ECG machines where
computer averages a few complexes and displays them as
linked median or computer averaged ECG, basically to rectify
the baseline movement of raw ECG. There can be an erroneous
representation based on the sampling. A narrow QRS rhythm
is represented as wide QRS because of intermittent premature
ventricular contractions (PVCs), which are only averaged (Fig.
4A); or in nonsustained VT, the narrow QRS complexes are
averaged misrepresenting as narrow QRS rhythm (Fig. 4B). At
times the PVC is averaged resulting in fallacious U wave (Figs 5A
and B). In absence of any tachycardia, the averaging of artifacts is
represented as SVT (Fig. 6). These have often been called “hightech” arrhythmias. It is essential that a non-averaged raw ECG
can be evaluated always not only for ST segment deviation, but
also for all arrhythmia diagnosis.
Fig. 2: Limb tremor artifact appearing as atrial flutter. Lead I and III suggest flutter (left arm tremor) but the
simultaneous acquired lead II clarify sinus rhythm
CHAPTER 43: Electrocardiogram: Pitfalls in Diagnosis and Artifacts
Fig. 3: ECG scope monitoring showing bradycardia in first strip with low voltage; second strip cable artifact appearing as VT; and
third strip after incorrect use of defibrillation, atropine and adrenaline
Abbreviations: ECG, electrocardiogram; VT, ventricular tachycardia.
Figs 4A: Sinus tachycardia with unifocal PVCs, wrongly diagnosed as VT due to compute averaging of only the PVCs
Abbreviations: PVCs, premature ventricular contractions; VT, ventricular tachycardia; SVT, supraventricular tachycardia
241
242
SECTION 4: Cardiac Investigation
Fig 4B: Repetitive nonsustained VT, wrongly displayed by computer averaging as SVT
Abbreviations: PVCs, premature ventricular contractions; VT, ventricular tachycardia; SVT, supraventricular tachycardia.
A
B
Figs 5A and B: (A) Abnormal appearing U waves due to fallacious computer averaging of a PVC; (B) A raw 12 lead ECG of
patient in Figure 1A, revealing no abnormal U waves
Abbreviations: PVCs, premature ventricular contractions; ECG, electrocardiogram.
CHAPTER 43: Electrocardiogram: Pitfalls in Diagnosis and Artifacts
Fig. 6: A young man during stress test, the ECG suggests SVT; however, the raw rhythm reveals cable artifact and noise,
which is wrongly averaged by the computer
Abbreviations: ECG, electrocardiogram; SVT, supraventricular tachycardia.
CONCLUSION
Electrocardiogram being a very important diagnostic tool and
used very frequently needs to be interpreted correctly, more so in
the era of computerization. It needs to be emphasized that ECG
diagnosis can be accurate when interpreted along with history
and physical examination findings, and in some situations with
other tests like cardiac enzymes and echocardiography. A raw
and appropriately filtered ECG should be used for diagnosis and
not computer averaged (as this is not a true ECG). Understanding
sampling error, electrical noise, hand/body tremors and cable
artifacts are essential to avoid wrong diagnosis and prescription
of wrong therapy.
ACKNOWLEDGMENT
The authors thank Dr. Martin Green for allowing to use his ECG
example (Fig. 2).
REFERENCES
1. Caceres L, Cooke D, Zalenski R, et al. Myocardial infarction with an
initially normal electrocardiogram--angiographic findings. Clin Cardiol.
1995;18(10):563-8.
2. François SJ, Erne P, Urban P, et al. Impact of a normal or non-specific
admission ECG on the treatment and early outcome of patients with
myocardial infarction in Swiss hospitals between 2003 and 2008. Swiss
Med Wkly. 2010;140:w13078.
3. de Zwaan C, Bär FW, Wellens HJ. Characteristic electrocardiographic
pattern indicating a critical stenosis high in the left anterior descending
coronary artery in patients admitted because of impending myocardial
infarction. Am Heart J. 1982;103(4 Pt 2):730-6.
4. Hayashi M, Denjoy I, Extramiana F, et al. Incidence and risk factors of
arrhythmic events in catecholaminergic polymorphic ventricular
tachycardia. Circulation. 2009;119(18):2426-34.
5. Obeyesekere MN, Klein GJ, Modi S, et al. How to perform and interpret
provocative testing for the diagnosis of Brugada syndrome, long-QT
syndrome, and catecholaminergic polymorphic ventricular tachycardia.
Cir Arrhythm Electrophysiol. 2011;4(6):958-64.
6. Roberts JD, Gollob MH. Early repolarization: a rare primary arrhythmic
syndrome and common modifier of arrhythmic risk. J Cardiovasc
Electrophysiol. 2013;24(7):837-43.
7. Mirvis DM, Goldberger AI. Electrocardiography. In: Bonow RO, Mann
DL, Zipes DP, Libby P (Eds). Braunwald’s Heart Disease: A Textbook of
Cardiovascular Medicine, 9th edition. Philadelphia, PA, USA: Elsevier
Saunders; 2012. pp. 126-67.
8. Sgarbossa EB, Pinski SL, Barbagelata A, et al. Electrocardiographic
diagnosis of evolving acute myocardial infarction in the presence of
left bundle-branch block. GUSTO-1 (Global Utilization of Streptokinase
and Tissue Plasminogen Activator for Occluded Coronary Arteries)
Investigators. New Engl J Med. 1996;334(8):481-7.
9. Harrigan RA, Chan TC, Brady WJ. Electrocardiographic electrode misplacement, misconnection, and artifacts. J Emerg Med. 2012;43(6):
1038-44.
10. Odman S, Oberg P. Movement-induced potentials in surface electrodes.
Med Biol Eng Comput. 1982;20(2):159-66.
11. Greutmann M, Horlick EM. Uncommon cause for a common
electrocardiographic artifact. Can J Cardiol. 2010;26(1):e30.
12. Ask P, Oberg PA, Odman S, et al. ECG electrodes: A study of electrical
and mechanical long-term properties. Acta Anaesthesiol Scand.
1979;23(2):189-206.
13. Patterson RE. The electrical characteristics of some commercial ECG
electrodes. J Electrocardiol. 1978;11(1):23-6.
243