Table of contents
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VT vs. SVT With Aberrancy
- There are a number of ways to distinguish VT from SVT with aberrant conduction (such as LBBB or RBBB).
- The most common technique is to look for features of VT:
- Highly atypical RBBB or LBBB pattern
- (or does not fit a bundle branch block)
- AV Dissociation
- (approximately 50% of VT has retrograde AV node (and atrial) conduction, and dissociated P-waves may not be seen).
- Extreme QRS Axis
- (i.e. positive in aVR, negative in I, II)
- Fusion Complexes
- (where sinus beats travel down the AV node and depolarize part of the ventricle using the usual His-Purkinje conduction. These beats "fuse" with the wide ventricular depolarization created by VT).
- Capture Beats
- Sinus depolarization travels down the AV node and depolarizes the ventricle to generate patient's baseline QRS complex. If it depolarizes at the same time as VT depolarization, a fusion complex is created.
- Other Features
- Highly atypical RBBB or LBBB pattern
- Multiple Criteria have been developed to help distinguish VT vs. SVT with aberrancy.
- Many have excellent operating characteristics:
- Brugada Criteria (Sn 0.987, Sp 0.965)
- R-Wave Peak Time (Sn 0.93, Sp 0.99)
- aVR Criteria (Sn 0.96, Sp 0.98) [aka Vereckei Criteria]
Brugada Criteria
- Sensitivity: 0.987
- Specificity: 0.965
- NOTE: R to S interval is measured from the ONSET of the R-wave to the NADIR of the S-wave
R-Wave Peak Time
- By Pava et al (2010) Heart Rhythm Society
- In Lead II measure onsent of QRS to peak of R-wave: (Image Credit: ECGpedia)
- Sensitivity: 93.2% (NPV 93)
- Specificity: 99.3% (PPV 98)
- LR+ 51
- LR- 0.06
- k=0.86 (interobserver reliability)
AVR Criteria
- Criteria to distinguish VT vs SVT w/ abberancy only based on aVR
- Vereckei et al 2008 - Heart Rhythm Journal
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NOTE: Step 4: Represents speed of ventricular activation
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Vi = mV traveled by ECG in first 40ms of QRS
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vf = mV traveled by ECG in last 40ms of QRS
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Sensitivity: 96.5% (NVP 86.6%)
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Specificity: 98.2%
Idiopathic VT
- Where after investigations, pathology is unknown (i.e. no structural heart disease)
Type of VT | QRSmorphology/axis | Pharmacoterapy sensitivity | Treatment |
RVOT VT /monomorphic extrasystoles | LBBB/ inferior axis | Adenosine, B-blocker, verapamil (or diltiazem) B-Blocker, verapamil | RF ablation |
LVOT VT | S wave in lead I, R-wave transition in V1 or V2 LBBB morphology, inferior axis, small R-wave in V1, early precordial transition (R/S=1 by V2 or V3) or RBBB morphology, inferior axis, S-wave in V6 | Adenosine, B-blocker, verapamil (or diltiazem) B-Blocker, verapamil, | RF ablation |
Fascicular VT | RBBB/ left superior axis (exit posterior fascicle); RBBB/right inferior axis (exit anterior fascicle) | Verapamil | RF ablation |
Outflow Tract Tachycardias
- Tachycardias that localize in and around RV or LV outflow tract
- Most common (80-90% of cases of idiopathic VT)
- Two most common presentations:
- Nonsustained, repetitive, monomorphic VT (60-90%)
- Frequent ventricular ectopy
- RV couplets
- Salvos of NSVT (LBBB morphology and inferior QRS Axis)
- Occur more often during the day, at rest, or following exercise.
- Diminish during exercise stress testing: (Transiently suppressed by sinus tachycardia)
- Paroxysmal, exercise-induced sustained VT
- Initiated during exercise or recovery
- Exercise stress testing initiates RVOT VT (but not helpful usually)
- Nonsustained, repetitive, monomorphic VT (60-90%)
- Symptoms:
- palpitations
- Presyncope is uncommon (syncope in minority)
- Investigations:
- ECG: Normal
- Echo: Structurally normal heart
- MRI: 70% have abnormalities in RV (focal thinning, diminished wall thickening in systole, abnormal wall motion)
- DDx: ARVD, atriofascicular (Mahian Fibers) tachycardia
- Should be distinguished from ARVD
- RVOT-VT and ARVD similar morphology of VT
- RVOT-VT terminates with adenosine (not ARVD)
- ARVD 12-lead ECG typically shows inverted T-waves in right precordial leads
- Epsilon wave in V1/V2 can be seen
- Treatment
- Acute
- Terminate with vagal maneuver
- or adenosine (6mg until 24mg)
- or verapamil (10mg over 1min) [suppress triggered rhythms]
- If hemodynamically unstable --> cardiovert electrically
- Terminate with vagal maneuver
- Chronic
- Medical Therapy vs. Ablation
- Decide based on severity of symptoms.
- Medical Therapy (mild-to-mod sx - efficacy 20-50%)
- B-blockers
- Verapamil
- Diltiazem
OR - Class IA, IC, and III agents
- Ablation
- 90% efficacy (5% recurrence in first year)
- Consider for: drug refractory VT, drug intolerance, desire not to use long-term drugs
- Especially for: Syncope, very fast VT, PVCs with short coupling interval
- Acute
Fascicular VT (aka Belhassen VT)
- First described by Zipes et al (1979)
- Induction with atrial pacing
- RBBB morphology with LAD
- Occurence of patients without structural heart disease
- 1981 Belhassen found the last feature:
- Can be terminated with verapamil
- Demographics:
- Occurs ages 15-40yo, male predominance
- Presentation:
- Palpitations, fatigue, dyspnea, dizziness, presyncope.
- Syncope and sudden death are VERY RARE
- Most symptoms occur at rest, but can trigger with exercise and emotional stress
- Investigations:
- ECG (baseline): normal (may have inverted Ts after a run of tachycardia due to memory)
- ECG (during VT):
- RBBB
- Left superior axis (suggesting exist site from infero-posterior ventricular septum)
- QRS 140-150ms duration
- Duration from QRS onset to nadir of S-wave in precordial leads is 60-80ms
- Can be hard to distinguish from SVT with RBBB+LAFB, best bet is to show:
- VA dissociation
- Rapid atrial pacing during tachycardia
- Management:
- Long-term prognosis without structural heart disease is good!
- VT may not progress (even without drugs)
- Medical Therapy:
- Pts with moderate symptoms can be treated medically
- Oral verapamil (120-480 mg/day)
- Ablation
- Ablation appropriate if:
- Severe Symptoms, intolerant or resistant to antiarrhythmic therapy.
- Target earliest high-frequency Purkinje potential during VT
- 92% success rate (rare complications - MR due to catheter entrampment in cordae, AR due to valve damage using retrograde aortic approach)
- Ablation appropriate if:
- Example of Fascicular VT:
- Features:
- RBBB + LAFB
- Differential includes: SVT with aberrancy (such as AT, AVNRT, AVRT with RBBB+LAFB)
- However, notice that some P-waves are missing, which means that this tachycardia does not depend on them. Hence this is fascicular VT!
- Features:
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