Sections View Full Chapter Figures Tables Videos Full Chapter Figures Tables Videos Supplementary Content +++ ECG Findings ++ Wide complex, regular tachycardia (usually > 140 bpm) QRS morphology consistent with one of the bundle branch block patterns +++ Pearls ++ The rapid rate of an SVT may “outrun” the ventricular conducting system’s ability to repolarize quickly, producing a rate-related bundle branch block. The signal then must propagate cell to cell, producing a wide-complex tachycardia. A typical bundle branch pattern usually results. When a person with a chronic wide-complex (aberrant) bundle branch block enters an SVT, the ECG will display a wide-complex, regular tachycardia. However, when the patient does not have prior ECGs, it can be difficult to distinguish SVT with aberrancy from a ventricular tachycardia (VT). Many different criteria have been proposed to distinguish the two, but unfortunately, most are neither extremely sensitive nor specific. When in doubt, treat as a VT, as many of the typical SVT pharmacologic agents are detrimental in patients with VT and can lead to ventricular fibrillation and death. ++ FIGURE 23.32A Supraventricular Tachycardia with Aberrant Conduction, Underlying RBBB. (ECG contributor: Walter Clair, MD.) Graphic Jump LocationView Full Size|Favorite Figure|Download Slide (.ppt) ++ FIGURE 23.32B Wide-complex tachycardia with a rate of 188 bpm. This patient has sudden onset of SVT with a known underlying RBBB. QRS complexes are wide (lower double arrows) and R-R intervals are regular (upper double arrows). Graphic Jump LocationView Full Size|Favorite Figure|Download Slide (.ppt) ++ FIGURE 23.32C Wide-complex tachycardia at approximately 150 bpm. The R-R interval is regular, except for one pause, when characteristic atrial flutter waves are apparent (arrowhead). Graphic Jump LocationView Full Size|Favorite Figure|Download Slide (.ppt) ++ FIGURE 23.32D Irregularity in the R-R interval, as seen most easily in the baseline (double arrows), strongly suggests the presence of rapidly conducted atrial fibrillation with aberrancy. Graphic Jump LocationView Full Size|Favorite Figure|Download Slide (.ppt) GET ACCESS TO THIS RESOURCE Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth Get Free Access Through Your Institution Contact your institution's library to ask if they subscribe to McGraw-Hill Medical Products. Access My Subscription GET ACCESS TO THIS RESOURCE Subscription Options Pay Per View Timed Access to all of AccessMedicine 24 Hour $34.95 (USD) Buy Now 48 Hour $54.95 (USD) Buy Now Best Value AccessMedicine Full Site: One-Year Individual Subscription $995 USD Buy Now View All Subscription Options