idiopathic Ventricular Tachycardia

• Idiopathic ventricular tachycardia (VT) is monomorphic VT that is not associated with structural heart disease.
• Idiopathic VT can be classified into 5 main types based on the locations in the heart it originates from:
    Outflow tract VT: most common idiopathic VT, from either right or left ventricular outflow tract (RVOT or LVOT)
    Fascicular VT: from either left anterior fascicle, posterior fascicle, or septal fascicle
    Annular VT: from either mitral or tricuspid annulus
    Intracavitary VT: from either papillary muscle or moderator band
    Epicardial VT: from crux
• General rule for localizing idiopathic VT based on ECG features:
    QRS morphology: RBBB ~ LV; LBBB ~ RV, septum, or aortic cusps
    Axis: inferior axis ~ base, anterior, lateral; superior axis ~ posterior
    Precordial transition: late ~ RV, early ~ LV, septum
    R/S ratio in V6: > 1 ~ base (outflow tract, annulus); < 1 ~ mid-ventricle (papillary muscle, fascicle)

• Outflow tract VT arises from delayed afterdepolarizations (DADs) in right or left ventricular outflow tract (RVOT or LVOT).
• Anatomically,
    RVOT includes pulmonary artery exit
    LVOT includes aortic root, aortic cusps, aorto-mitral continuity (AMC)
• In general on ECG, there are:
    Positive R waves in II, III, aVF
    Deep S waves in aVR, aVL
    Inferior axis
    LBBB or RBBB morphology (in RVOT or LVOT, respectively)
• More common in women, age range 30-50s.

• Fascicular VT (also referred to as "idiopathic left VT", "Belhassen tachycardia", or verapamil-sensitive VT") is caused by reentry circuit involving either left posterior (most common), left anterior, or left septal fascicle.
• Since VT is conducted down the Purkinje system, QRS's are relatively narrow (< 140 ms) with RS interval < 80 ms (normally needs to be > 100 ms to meet Brugada criteria for VT). For this reason, fascicular VT can be difficult to distinguish from SVT with aberrancy
• More common in men, age range 20-40s.

• Annular VT arises from either mitral or tricuspid annulus.
• ECG shows typical VT features but with broad R in V1 and rightward or inferior axis (around 90 degree).
• More common in men, age range 50-70s.

• Intracavitary VT arises from either papillary muscle or moderator band.
• More common in men, age range 40-70s.

• Epicardial VT originates from:
    Crux: at the junction of atrioventricular groove & posterior interventricular groove, also junction of middle cardiac vein (MCV) & coronary sinus (CS), near the origin of PDA
    LV summit: at the junction of anterior interventricular vein (AIV) & great cardiac vein (GCV), also bounded by LAD & LCx
• Epicardial VT takes longer to reach to subendocardium, where Purkinje network is located, and propagates from LV free (lateral) wall or posterior wall to medial or superior wall, respectively. As a result, on ECG:
    QRS > 200 ms
    R wave peak time (RWPT) > 85 ms
    MDI (RWPT/QRS) > 0.54
    Pseudo-delta wave > 34 ms
    RS > 121 ms
    QS pattern in I or aVF