Wide Tachycardia

    .

     

    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
    • 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

     

    • brugadaCriteria.png     brugadaCriteria2.png

     

    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)
      • RWPT.png

      • Note: Even if the first deflection is negative, find the first R-wave

    • 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
    • avrCriteria.png

    • NOTE: Step 4: Represents speed of ventricular activation

      • Vi = mV traveled by ECG in first 40ms of QRS

      • vf = mV traveled by ECG in last 40ms of QRS

    • Sensitivity: 96.5% (NVP 86.6%)

    • 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

     

    • RVOTLVOT-VT2.png

     

    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)
    • 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
      • 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

     

    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)
    • 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!

    eVT22a.png

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