Ventricular Tachycardia



Ventricular Tachycardia


Christopher P. Kovach, MD, MSc

Mala M. Sanchez, MD





How can VT and SVT with aberrancy be distinguished by ECG?

Algorithmic ECG interpretation approaches can be used to differentiate VT from SVT with aberrancy. In particular, the presence of atrioventricular (AV) dissociation or precordial QRS concordance or northwest QRS axis (>270°) by ECG is nearly 100% predictive of VT.

In a narrative review,1 authors discussed selected studies published over a period of 50 years that focused on deriving and/or validating the ability of ECG findings to predict VT. Stratifying their findings by QRS morphology, the authors reported positive predictive value (PPV) for a range of ECG findings (Table 23.1). Of these, they found that the presence of AV dissociation, QRS concordance in the precordial leads, and extreme “northwest” QRS axis (i.e., >270°) were the most suggestive of VT in both left and right bundle branch QRS morphologies. Three ECG findings that suggest AV dissociation are (1) QRS complexes occurring more rapidly than, and independently of, P waves, (2) the presence of intermittent normal, nonwide QRS complexes interrupting the WCT (known as “capture beats”), and (3) the presence of hybrid atrial/ventricular complexes interrupting the WCT (known as “fusion beats”).









TABLE 23.1 PPV of Specific ECG Criteria for the Identification of VT







































LBBB/RBBB Morphology


AV dissociation


100%


Precordial concordance


89%-90%


Northwest axis


95%-96%



LBBB morphology


QRS width >160 ms


98%-99%


Right axis deviation


87%-96%



RBBB morphology


RSR’ in V1 (left peak > right peak)


100%


Left axis deviation


88%-96%


QRS width >140 ms


89%


AV, atrioventricular; LBBB, left bundle branch block; RBBB, right bundle branch block; VT, ventricular tachycardia.


Adapted from Garner JB, Miller JM. Wide complex tachycardia – ventricular tachycardia or not ventricular tachycardia, that remains the question. Arrhythm Electrophysiol Rev. 2013;2(1):23-29.


Multiple algorithms for interpreting ECG findings and differentiating between VT and SVT with aberrancy have been established. A retrospective analysis2 of 260 WCTs evaluated the performance characteristics of the Brugada, Bayesian, Griffith, lead aVR, and lead II R-wave peak time algorithms in a sample of 204 patients. ECGs from unselected, consecutive patients were analyzed using algorithms by a blinded cardiologist and cardiac electrophysiologist. Ultimate diagnoses were confirmed by the study team via either electrophysiology (EP) study, intracardiac ECG from an implanted device, or subsequent ECGs. The algorithms were found to have similarly moderate diagnostic accuracy for VT (i.e., arrived at the correct diagnosis approximately 69%-77% of the time). The Brugada algorithm was found to have superior accuracy compared to R-wave peak time (P = .04).




Which antiarrhythmic drugs can be used to terminate stable VT?

Several medications have efficacy for terminating stable VT, including amiodarone, lidocaine, and procainamide. In particular, evidence supports the effectiveness of procainamide.

This question was addressed in a 2013 systematic review3 that screened 574 studies and ultimately identified 5 high-quality studies (3 prospective, 2 retrospective) comparing the effect of IV antiarrhythmics on stable VT. Studies measuring the suppressive effect of IV drugs on electrophysiologic inducibility of VT were excluded. The authors determined that procainamide was superior to lidocaine (RR 2.2, 95% CI 1.2-4.0; P-value not reported; number needed to treat [NNT] 2.5) but that amiodarone and procainamide were equivalent (RR 4.3, 95% CI 0.8-23.6; NNT 3.0). A major study caveat was limited available evidence.

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Feb 5, 2020 | Posted by in CRITICAL CARE | Comments Off on Ventricular Tachycardia
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