Transcript Differential Diagnosis of Wide QRS Complex Tachycardia

Differential Diagnosis
of Wide QRS Complex
Tachycardia
Gholamreza Davoodi M.D
Tehran Heart Center
TUMS
Importance of diagnosis of WCT
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-Correct diagnosis is important both for acute
management and also subsequent management.
-If we inject verapamil to a patient with VT and low EF
, prolonged hypotension and hemodynamic
deterioration happens.
-Non of the criteria is perfect but they can be helpful.
-The clinical situation of the patient with WCT usually
don’t allow leisurely analysis of ECG ,so the criteria
must be not only accurate but easily applied and easily
remembered.
Definitions
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-WCT :Rate equal or more than 100 and QRS duration
of at least 120 msec.
-VT :a WCT originating below the level of His bundle.
-SVT : a tachycardia dependent on participation of
structures at or above the level of His bundle.
-LBBB morphology: QRS duration more than 120 with
predominantly negative terminal deflection in V1.
-RBBB morphology : QRS duration more than 120 and
a terminal positive deflection in V1.
-LBBB and RBBB morphology denote the appearance
of QRS , without implying actual His-Purkinje disease.
Differential Diagnosis of WCT
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-Ventricular tachycardia (about 80% of cases ).
-SVT with abnormal interventricular conduction (15-30 %):
*SVT with BBB aberration (fixed or functional).
*Pre-excited SVT (SVT with ventricular activation occurring
over an anomalous AV connection ).Their ECG can be
indistinguishable from VT originating at the base of ventricle.(15 % of all)
*SVT with wide QRS due to abnormal muscle-muscle spread
of impulse.( surgery, DCM)
*SVT with wide complex due to drug or electrolyte-induced
changes. (hyperkalemia. Class Ia ,Ic drugs or Amiodarone)
-Ventricular paced rhythms .(small but growing percentage )
SVT vs VT
History
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-The majority of patients with VT have
structural heart disease, In SVT they may or may
not have.
-Patient with VT are older.
-Patients with SVT more often have history of
previous similar episodes .(cutoff of 3 years)
SVT vs VT
Physical examination
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-Overall appearance of patient is not accurate.
-The widespread impression that hemodynamic stability indicates
SVT is erroneous and can lead to dangerous mistreatment.
-Physical findings that indicate presence of AV dissociation
(cannon A waves, variable-intensity S1,variation in BP unrelated
to respiration) if present are useful.
-Termination of WCT in response to maneuvers like Valsalva,
carotid sinus pressure, or adenosine is strongly in-favor of SVT
but there are well-documented cases of VT responsive to these.
-Diagnostic injection of verapamil or beta-blockers should be
discouraged. (prolonged hypotension).
SVT vs VT
ECG criteria
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-A fundamentally simple approach: If WCT is due to
SVT with aberration, the QRS must be compatible with
some form of BBB or FB.
-QRS duration:70% of VTs have QRS duration >140,
but no SVT has it. VT is probable when QRS> 140
with RBBB and >160 with LBBB pattern.Anti
arrhythmic drugs may prolong QRS. Some patients
with VT may have QRS of 120-140 specially in those
without structural heart disease.
SVT vs VT
ECG criteria contd,
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-QRS
axis:
*The more leftward the axis , the more probable VT.
* The quadrant between -90 and 180 (northwest )can’t
be achieved with any combination of FB or BBB.
*Some has suggested that if the axis in sinus rhythm is
more than 40 degrees different with WCT the diagnosis
is VT , but it is not widely accepted.
SVT vs VT
ECG criteria contd
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-Specific morphologies ;
If with RBBB pattern:
*In V1:During aberration there is no change in initial
portion of QRS so we may see rSr’ ,rR’ , rsr’ or rSR’.
But a monophasic R wave , or a broad (> 30 msec) R
with any following terminal QRS forces or qR are
highly suggestive of VT.
* In V6 :During aberration qRs , Rs ,or RS (with R/S
ratio >1) are seen but in VT we may see rS,Qrs , QS or
QR or monophasic R wave. If RS pattern is present
R/S must be less than 1.
SVT vs VT
ECG criteria contd
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LBBB pattern:
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* In V1 :Either rS or QS with rapid initial forces (narrow R
with rapid smooth descent to S )is seen in LBBB type aberration.
Any other pattern such as broad R/deep S or QS with slow
descent to S wave nadir will imply VT.
If the initial R is wider than 30 msec it suggest VT , the wider
the R , the greater the likelihood of VT.
Notching in the down-stroke of S or interval from the onset of
QRS to the S wave nadir greater than 60 msec strongly suggest
VT.
*In V6 :In aberrancy there is no initial Q wave and we see RR’,
or monophasic R. During VT common patterns are QR ,QS
,QrS ,or Rr’ although patterns compatible with SVT may also be
seen.
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SVT vs VT
ECG criteria contd
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Combination of LBBB and RAD is almost always due
to VT .
RBBB with a normal axis is very uncommon in VT.
Concordant pattern in precordial leads is uncommon in
SVT ,with the exception of pre-excited tachycardia
.The specificity of concordant pattern for VT is >90%
but sensitivity is low(20%).
Negative concordance in limb leads is another way of
describing NW axis and suggests VT.
SVT vs VT
ECG criteria contd
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Q waves during WCT show old MI and are in
favor of VT. Generally patients with old Q
waves maintain it during WCT .
Some patients with DCM may have Q during
VT while they don’t show it in SR.
Pseudo Q waves may be seen in some SVTs
with aberrancy. (AVNRT or pre-excited with a
posterior AV connection ).
SVT vs VT
Precordial RS absent criteria
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Brugada: Most SVTs with aberrancy have an RS
complex in at least one precordial lead. VT need not
have so in the absence of it the probable diagnosis is
VT.
In the presence of RS if the interval from onset of R
to nadir of S was greater than 100 msec ,VT was
diagnosed.
These criteria are an extension of the dictum that if the
ECG doesn’t look like aberration , it is most likely VT.
AV dissociation
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Is the most useful criteria.
Complete AVD is seen in 20-50% of all VTs and practically no SVTs.
(specificity near 1)
15-20 %of VTs have second degree VA block.
Another clue to the presence of AVD is variation in QRS amplitude.
(summation of p on QRS or variable ventricular filling).
30% of VTs have 1:1 retrograde conduction. Faster VTs are less likely to have
1:1 conduction but there is no cut-off.
Carotid pressure or adenosine can cause transient VA block and show VT.
Fusion beats imply the presence of AVD (most often seen during slow
tachycardias). It is most reliable when it is a clear fusion and not a simply
change in morphology. Which can be due to PVC during VT. PVCs can fuse
with SVT beats which can erroneously be taken as VT.
SVT vs VT
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WCT with QRS narrower than NSR is strongly in favor
of VT.
Contralateral BBB in NSR and WCT strongly suggests
VT. Because if RBBB is present in SR and LBBB
develops with SVT, then CHB must happen. (except in
rare cases).
QRS alternans is not an important diagnostic factor.
Presence of multiple WCT configurations is in favor of
VT.
Special cases of WCT
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Pre-excited SVTs (ventricular activation entirely or
primarily over an anomalous AV connection) has an
ECG pattern consistent with VT.
In BB reentry the ECG criteria suggest SVT, but it is
VT.(AVD is frequent in these patients and helps ).
Both SVT and VT are usually regular, marked
irregularity is in favor of AF but remember that VTs
can be irregular particularly in the first 30 seconds of
the episode. VTs with CL irregularity are usually seen in
patients taking anti -arrhythmic drugs.
Narrow QRS complex VT
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VT can have QRS duration less than the cutoff
of 140 msec. Possible explanations are:
1-Septal origin of VT.
2- Early penetration in the His- Purkinje system.