There are several algorithms that are currently used to help distinguish Supraventricular Tachycardia (SVT) with aberrancy and Ventricular Tachycardia (VT). Many of these algorithms lack specificity, and let’s face it, who can remember if the absence of an RS complex in the precordial leads is VT or SVT with aberrancy. So what if there was a criterion that had a good sensitivity (SN), specificity (SP), and was one simple step?
What are some of the algorithms used to differentiate SVT with aberrancy and VT?
- Brugada Algorithm (Most commonly used): SN 89%, SP 59.2%1 (ALiEM post, PV card)
- Vereckei aVR Algorighm: SN 87.1%, SP 48% 2 (PV card)
- Bayesian Algorithm: SN 89%, SP 52% 3
- Griffith (Bundle Branch Block) Algorithm: SN 94.2%, SP 39.8% 4
What is the R-Wave Peak Time (RWPT) in lead II?
- Duration from the QRS depolarization onset until the first change of polarity (independent of whether the QRS deflection is positive or negative) as measured in lead II
- Another way to think of this is, duration from the isoelectric line to its first deflection
Image from ECGPedia.org
Why is lead II used and not other leads?
- Almost always present on ECG rhythm strips recorded in different settings
How good is RWPT in lead II at differentiating between SVT with aberrancy and VT? 5
- In a retrospective study of 218 wide complex tachycardia ECGs, RWPT ≥ 50 msec had a positive LR of 51.3
| Test | Value |
| Sensitivity | 93.2% |
| Specificity | 99.3% |
| Positive Predictive Value | 98.2% |
| Negative Predictive Value | 93.3% |
- A 2013 study (n=69) showed lower sensitivity numbers for the RWPT ≥ 50 msec criterion – SN 67% and SP 97% 6
Is RWPT ≥ 50 msec more accurate than QRS width ≥ 130 msec in lead II for differentiation of wide complex tachycardia? 5
- Yes
- QRS width ≥ 130 msec in lead II: SN 83.33% and SP 58.97%
If this criterion is so sensitive, specific, and easy to use, why don’t we use it instead?
- There is some difficulty in defining the initiation and peak of ventricular complexes
- Further prospective studies need to validate this rule
Conclusion
RWPT ≥ 50 msec in lead II seems to be simple, reproducible, and highly sensitive and specific for VT, but more prospective studies need to be performed to validate this rule.
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