The ECG shown below was obtained from a
patient whose blood pressure was dropping.
- How many reasons can you cite to support a
diagnosis of VT (Ventricular Tachycardia)?
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| Figure 1: 12-lead ECG obtained from a patient whose BP was dropping. – NOTE – Enlarge by clicking on Figures. – Right-click to open (and keep open) in a separate window. |
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NOTE: Because of the length of this Blog - We offer all Tables and Figures at this LINK (on Blog 42-bis) - so as to facilitate side-by-side viewing. Tables/Figures are also found here at the bottom.
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ANSWER to Figure 1:
The 12-lead ECG in the Figure shows a regular WCT (Wide Complex Tachycardia)
rhythm at a rate of ~180/minute. Sinus P waves are absent. The rhythm is sustained
VT – and the patient is in need of immediate electrical therapy (synchronized
cardioversion or defibrillation). Many reasons can be cited to support
definitive diagnosis of sustained VT. These include:
1) Statistically – at least 80% of all regular
WCT rhythms of uncertain etiology are VT. The likelihood of VT increases to over
90% IF the patient is middle-aged or older – and especially if the patient has
underlying heart disease.
- Although on occasion regular WCT rhythms may
be due to a supraventricular etiology with either preexisting bundle branch
block or aberrant conduction – VT must always be assumed until proven otherwise
(See Table 1 below or at 42-bis). In addition to being so much more common than wide-QRS
complex SVT rhythms – VT is a potentially life-threatening arrhythmia.
2) Extreme axis deviation is present. Mild-to-moderate
left or right axis deviation may be seen with supraventricular rhythms.
However, total negativity in either lead I or lead aVF suggests extreme axis
deviation, and is virtually diagnostic of VT.
3) The QRS complex is both markedly widened (to
over 0.16 second in many leads) – and – the QRS is lacking in organized morphology
(which we convey by describing QRS appearance as “ugly”…). Both features are
highly suggestive of VT. Aberrant conduction most often manifests a more
organized QRS morphology that is consistent with some type of conduction defect
(left or right bundle branch block with or without hemiblock).
4) There is ECG evidence of delayed initial ventricular
activation. The presence of an r-to-S-nadir of more than 0.10 second in one or
more precordial leads is highly suggestive of VT. This is best seen in lead V5.
5) One should always assume VT until proven
otherwise. The patient should be treated accordingly.
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KEY Clinical Principles to Apply for the
Patient in WCT:
Many ECG criteria have been cited to assist in
assessment of WCT rhythms. We extensively review this topic elsewhere (See ACLS
Comments- ISSUE #11). For the purposes of this ECG Blog #42 – We consolidate
key principles as they apply to the ECG and clinical scenario presented in Figure
1.
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Our Suggested Approach to the patient in a WCT
rhythm is as follows:
- First determine IF the patient is hemodynamically
stable. IF the patient is unstable – it no longer matters what the rhythm is,
since immediate electrical therapy (synchronized cardioversion or
defibrillation) is indicated.
- IF the patient with tachycardia is initially
stable – BUT at any time becomes unstable – electrical therapy is then
immediately indicated.
- IF the rhythm diagnosis is known to be VT –
treat accordingly (See ACLS Comments – Issue #2).
- IF the rhythm diagnosis of the WCT rhythm is known
to be SVT – then a different approach should be followed, depending on our “best
guess” as to the etiology of the SVT (See ECG Blog #40 and ACLS Comments – Issue #9).
- Special considerations and treatment
interventions are warranted for the patient with stable but irregular WCT –
given the possibility of Torsades de Pointes, polymorphic VT, and very rapid
AFib with WPW (See ECG Blog #36 and ACLS Comments – Issue #5).
- But IF the patient is stable – and – the
rhythm is a regular WCT of uncertain etiology – then focused attention to a few
selected ECG Features can greatly increase the certainty of our presumed diagnosis.
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Which ECG Criteria to Use for Assessing WCT
Rhythms?
Many criteria exist for assessing WCT rhythms.
We list below our preference for those criteria we feel are: i) easy-to-use and
remember; and ii) very useful clinically:
- We start with 3 Simple Rules (Table 2). In our
experience – these 3 user-friendly Rules are all that is needed for near definitive
diagnosis of VT in most cases.
- RULE #1: Is there extreme axis deviation? IF
so – then VT is highly likely. We emphasize that mild or even moderate left or
right axis deviation (LAD or RAD) does not assist in distinguishing between VT
and SVT. But – when there is extreme axis deviation (as seen for the marked RAD
in Figure 1 – in which the QRS complex in lead I is entirely negative) – then
VT is almost certain.
- RULE #2: Look at QRS morphology in Lead V6.
When the etiology of the rhythm is supraventricular – there will almost always
be at least some positive activity traveling toward the LV (and therefore
positive in lead V6). IF ever the QRS complex in lead V6 is either all negative
or almost all negative – then VT is highly likely. We emphasize that lead V6 is
only helpful when it is predominantly negative. Thus, the positive R wave we
see in lead V6 of Figure 1 is not diagnostic (See Figure 2).
- RULE #3: The “uglier” the QRS complex during
the WCT rhythm – the more likely the rhythm is VT. The reason for this is that
aberrant conduction almost always manifests some form of conduction defect (RBBB,
LBBB, LAHB, LPHB – or some combination thereof) – due to relative delay in one
or more of the hemifascicles or bundle branches. In contrast – VT originates
from a ventricular focus outside of the conduction system (and is therefore
more likely to be wider and far less organized in its conduction pattern). The
QRS complex in Figure 1 is extremely wide (over 0.16 second) and formless. This
makes supraventricular conduction much less likely.
- Is there AV Dissociation during the WCT rhythm?
IF so – this is virtually diagnostic of VT. That said – most of the time, AV
dissociation will not be seen unless the rate of VT is relatively slow.
Therefore – the absence of AV dissociation is nondiagnostic. However, its
presence may be confirmatory. Although it is possible that 1:1 retrograde
atrial conduction may be seen in Figure 1 (in the form of subtle notching in
the ST-T wave of lead II and in lateral precordial leads) – normal sinus P
waves are clearly absent. Thus, there is no indication of AV dissociation.
- Is there Concordance of the QRS complex in all
precordial leads? IF ever all QRS complexes in leads V1-thru-V6 are either all
positive or all negative – this is virtually diagnostic of VT. That said – the
sensitivity of this finding is extremely low, such that the lack of precordial
lead concordance is not helpful. Concordance is not present in Figure 1 –
because the QRS is clearly positive in lead V6.
- Is the R-to-S nadir in any precordial lead delayed
to >0.10 second? Brugada’s 2nd criterion for assessing WCT rhythms (and
Sasaki’s 2nd criterion) specify delay in attaining the R-to-S nadir in any
precordial lead as highly suggestive of VT (See Figure 3). If no delay is
seen in attaining R-to-S nadir – then nothing can be said. The physiologic
rationale for the R-to-S nadir delay criterion is that the initial path of
supraventricular impulses is usually conducted with no more than minimal delay.
Most regular WCT rhythms will manifest an RS complex in at least one precordial
lead (IF there is no RS complex in any precordial lead – then by Brugada’s 1st
criterion the rhythm is VT!). The main caveat to be aware of is that the
boundaries of QRS onset and S wave nadir are not always clear. However – R-to-S
nadir in lead V5 of Figure 1 appears to definitely exceed 0.10 second in
duration.
- Is there a tall monophasic R wave in lead aVR?
With normal sinus rhythm – lead aVR manifests a predominantly negative QRS
complex. This reflects the normal path of ventricular activation – which moves away
from the right (away from aVR) – and toward the left ventricle. IF ever the QRS
complex in lead aVR during WCT is entirely positive – this means that the
electrical impulse must be originating from a site in the ventricular apex and
traveling upward toward the base (in the direction of aVR). Thus, a quick look
at lead aVR during a WCT rhythm can sometimes tell you (with virtual 100%
specificity) that the rhythm is VT (See Figure 4). That said – this
criterion is relatively insensitive, such that most of time QRS appearance in
lead aVR will be nondiagnostic. Lead aVR is nondiagnostic in Figure 1.
- Is QRS morphology typical of aberrant conduction?
For practical purposes – the only QRS morphology form with high specificity for
SVT is the presence of typical RBBB. By far the best lead to recognize this in
is lead V1 (See Figure 2 below). Thus, the presence of an rsR’ complex (with
‘taller-right-rabbit-ear’ and S wave that descends below the baseline) – strongly
suggests a supraventricular etiology (A,B in Fig. 2). In contrast – any other
QRS morphology in lead V1 (C,D,E,F) serves to increase the likelihood of VT.
This includes an upright, widened QRS with a notch that does not descend below
the baseline (C) – as well as a monophasic R without any notch (D) – a qR
pattern (E) - and/or a taller left rabbit ear with or without a notch (F).
Assessment of QRS morphology in Figure 1 – clearly does not resemble typical
RBBB (instead the QRS is entirely negative in lead V1). As already noted – QRS
morphology in Figure 1 is “ugly” (formless) – not suggestive of either typical
LBBB or RBBB – and therefore strongly in favor of VT as the etiology
- Clinical Parameters: While exceptions
definitely occur – the fact that a patient is “younger” and previously healthy
prior to the arrhythmia episode does make an ischemic form of VT much less likely.
In contrast, even before looking at specific ECG features – IF the patient
presenting with a regular WCT of uncertain etiology is “older” and has a
history of significant heart disease – then then statistical likelihood of VT approaches
90%.
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NOTES regarding Clinical Parameters:
- Is the patient “older” ? While there are no
specific age “cutoffs” for what is ‘older’ or ‘younger’ – a patient in their
20’s, 30’s or early 40’s is relatively more likely to have SVT than a patient
older than 55. This is especially true IF this younger adult was previously
healthy with no known underlying heart disease.
- A select group of VT rhythms (as many as 5-10%
of all VT rhythms) – may respond to Adenosine! While certain ECG characteristics
may suggest an adenosine-responsive form of VT (See Issue #2 and ECG Blog #35)
– ECG recognition of adenosine-responsive VT will not always be possible.
Awareness of this clinical reality provides a rationale for trial of empiric Adenosine
at an early point in the treatment approach to monomorphic regular WCT.
- Adenosine-responsive forms of VT – are much more
likely to occur in younger adults without underlying heart disease. They often
occur during exercise – and the patient will often remain hemodynamically
stable during the WCT rhythm. Thus, even IF a previously healthy young adult
presents with VT – the chances are surprisingly good that the rhythm will
respond to Adenosine. That said – the above discussion does not apply to the
case in Figure 1, because the patient was unstable and in need of immediate
cardioversion.
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SUMMARY:
Always think, “VT until proven otherwise” –
whenever you encounter a patient in a regular WCT rhythm of uncertain etiology.
Treatment will depend on hemodynamic stability and clinical parameters. Our
hope is that review of this ECG Blog #42 will increase your comfort in the relative
certainty of your rhythm diagnosis.
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Supportive Tables and Figures for this ECG
Blog #42 (also found at 42-bis):
- Included below are key visuals we refer to in
this ECG Blog #42 for assisting in differentiation of WCT rhythms (Please also see ACLS
Comments – ISSUE #11 for full interactive discussion of this topic! ):
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| Table 1: One should always assume VT until proven otherwise whenever you encounter a regular WCT without sinus P waves. Statistically – at least 80-90% of all regular WCT rhythms of uncertain etiology will turn out to be VT (which is why we list VT for the first 8-out-of-10 causes on this list). Less commonly – one may see a supraventricular etiology with either preexisting bundle branch block or aberrant conduction. |
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| Table 2: After applying Table 1 (ie, "Assume VT until until proven otherwise) - we move to the 3 Simple Rules - which in our experience is often all that is needed for near-definitive diagnosis. |
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| Figure 2: Attention to selected ECG features of QRS morphology may be helpful in ruling in or out VT. We focus on leads V1 and V6. The presence of either an entirely negative QS in lead V6 (complex J) or an almost entirely negative complex (I) – is highly suggestive of VT. In contrast – greater positivity in lead V6 (G,H) is nondiagnostic. Aberrant conduction is suggested by a typical rsR’ (taller-right-rabbit-ear) morphology in lead V1 (A,B). The presence of any other predominantly upright complex in lead V1 strongly suggests VT (C,D,E,F). We intentionally exclude reference to LBBB aberration in this figure – because both VT and SVT may manifest WCT rhythms that resemble LBBB. |
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| Figure 3: The finding of a delayed R-to-S nadir (to >0.10 second) in any precordial lead is highly suggestive of VT (1st example taken from lead V2). The absence of a delayed R-to-S nadir in any precordial lead is nondiagnostic. Shown above is an example (from lead V4) in which the very slender initial r wave and steep S wave downslope result in an R-to-S nadir that clearly does not exceed 0.10 second. |
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Figure 4: The presence of a large upright R
wave in lead aVR during a WCT rhythm is virtually diagnostic of VT (since this
finding implies ventricular activation begins in the apex). Finding a QR
complex or a small amplitude complex (2nd and 3rd examples shown) is
nondiagnostic.
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Selected REFERENCES:
- Brugada P, Brugada J, Mont L, et al: A New
Approach to the Differential Diagnosis of a Regular Tachycardia with a Wide QRS
Complex. Circulation 83:1649-1659, 1991.
- Blomstrom-Lundqvist C, Scheinman MM, Aliot EM, et
al: ACC/AHA/ESC Guidelines for Management of Patients with Supraventricular
Arrhythmias- Executive Summary. J Am Coll Cardiol 42:1493-1531, 2003.
- Vereckei A, Duray G, Szenasi G: Application of a
New Algorithm in the Differential Diagnosis of Wide QRS Complex Tachycardia. Eur
Heart J 28:589-600, 2007.
- Sasaki K: A New Simple Algorithm for Diagnosing
Wide QRS Complex Tachycardia: Comparison with Brugada, Vereckei and aVR
Algorithms. Circulation 120:S671, 2009.
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- See ACLS Comments: ISSUE #11 - for discussion discussion on differentiation between VT vs Aberrant Conduction.
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