Saturday, April 28, 2012

ECG Interpretation Review #41 (WCT - Wide Complex Tachycardia - Evaluation - SVT - Aberrant Conduction)

The patient is a 60-year-old man who presents to the ED (emergency department) with a chief complaint of palpitations and the ECG shown in Figure-1.
  • BP = 160/90 mm Hg at the time Figure 1 is recorded.
  • You know nothing more than that the patient has a history of "heart disease"  and that he is on a number of medications.
Figure-1: 12-lead ECG obtained on a 60-year-old man with a history of "heart disease" and palpitations. BP=160/90. (Figure reproduced from Figure 09.5-1 in ACLS-2013-ePub). - NOTE - Enlarge by clicking on Figures - Right-Click to open in a separate window.
  • What is the rhythm in Figure-1? How certain are you of your specific rhythm diagnosis?
  • How would you proceed clinically? Do you need to be certain of the rhythm diagnosis before initiating treatment?
  • Would you give Adenosine as your 1st drug? If so — What is the response you expect this drug to have?
  • What might be done to increase your level of certainty about the specific rhythm diagnosis for the tracing in Figure-1? Would definitive rhythm diagnosis change your therapeutic approach? If so — How?
ANSWERS: A regular WCT is seen at a rate of ~160/minute. There is no clear evidence of atrial activity. The differential diagnosis is that of a regular WCT (Wide-Complex Tachycardia) = VT, VT, VT until proven otherwise.
  • Given the patient’s age and history of “heart disease” — statistical likelihood of VT is ~90% without going further.
  • The above said — there IS a chance that the rhythm in Figure-1 could be SVT (with either aberrant conduction or preexisting BBB).
Figure-1: Approach When Uncertain of the Diagnosis
The 12-lead tracing in Figure-1 provides an excellent example of how to approach a WCT Rhythm when you do not know for sure what the diagnosis is (See Section 08.0,09.0 in the References below):
  • The patient is stable (ie, there is time to look further).
  • The WCT is regular. Therefore — the rhythm is not AFib.
  • The QRS is monomorphic (all QRS complexes in a given lead look the same). Thus, this is not polymorphic VT/Torsades.
  • Assessment of QRS morphology is inconclusive. That is — the ‘3 Simple Rules’ do not suggest VT (discussed in detail in Section 08.0 in the References below). Specifically — the axis during WCT is normal — lead V6 is upright – and – the QRS is not “ugly”, but instead is perfectly consistent with LBBB.
KEY: We don’t know for sure what the rhythm in Figure-1 is. Although our initial assessment does not point to a ventricular etiology — We still need to assume VT until proven otherwise. That said — the patient is stable and Adenosine is appropriate initial treatment (See Section 06.0 on Using Adenosine in the References below).
  • Failure of Adenosine — to either temporarily slow the rate or convert the rhythm would support the premise that the rhythm in Figure-1 is VT. At this point — We would then move on to Amiodarone (or other VT drug).
  • Successful conversion of the rhythm by Adenosine would support (but not definitely prove) a supraventricular etiology.
  • Remain ready to cardiovert — IF at any time the patient becomes hemodynamically unstable.
  • Ask someone to search this patient’s chart in the hope of finding a prior 12-lead ECG that might tell if this patient had baseline LBBB.
This case highlights a number of important points:
  • Definitive diagnosis of the rhythm in Figure-1 is not needed to effectively treat the patient. Instead we follow the course laid out for WCT of Uncertain Etiology (discussed in detail in Section 08.0 in the References below).
  • Use of the ‘3 Simple Rules’ does not point toward VT in this case (but these Rules still help as they make an SVT diagnosis more plausible).
  • Assessment of more advanced QRS morphologic features likewise fails to yield a definitive answer (See Section 08.0). That is — at least one rS complex is present in precordial leads (seen here in V2,V3,V4) and there is no delay in S wave downslope in V1,V2,V3. The initial r wave in lead V4 is not wide.
FINAL THOUGHT: Use of the 12-lead ECG during tachycardia confirms that the QRS complex in this tracing is wide. This is important — because the QRS did not look that wide in leads II and aVF. “12 leads are better than one!”
Use of the 12-lead during tachycardia is also helpful in clarifying questions about atrial activity. For example — one might wonder IF the upright deflection midway between QRS complexes in lead II (and in other leads) could be a sinus P wave? (arrows in Figure-2).
Figure-2: We’ve added arrows to Figure-1. There are no definite P waves (unless they could be hidden within the ST-T wave ...).
NOTE: While we cannot rule out the possibility that sinus P waves might be hiding within preceding T waves in Figure-2 (arrows) — lack of “telltale” atrial notching defines this rhythm as a monomorphic regular WCT of uncertain etiology. Ventricular tachycardia must be assumed until proven otherwise.
  • Access to a prior 12-lead ECG on this patient would favor SVT if LBBB with identical morphology was seen.
  • IF the patient remained stable — Use of a Lewis Lead might be attempted looking for atrial activity (See Section 10.0 in the References below).
Please Check out the following relevant PDF Sections excerpted from ACLS-2013-ePub:
NOTE: ECG Blog #42 - and - Blog #42-Bis — also review in detail with illustrative Tables the differentiation between VT vs SVT with Aberrant Conduction.

No comments:

Post a Comment