Differential Diagnosis of Wide QRS Complex Tachycardia

-Ventricular tachycardia (about 80% of cases ).
-SVT with abnormal interventricular conduction (15-30 %):
*SVT with BBB aberration (fixed or functional).
*Pre-excited SVT (SVT with ventricular activation occurring over an anomalous AV connection ).Their ECG can be indistinguishable from VT originating at the base of ventricle.(1-5 % of all)
*SVT with wide QRS due to abnormal muscle-muscle spread of impulse.( surgery, DCM)
*SVT with wide complex due to drug or electrolyte-induced changes. (hyperkalemia. Class Ia ,Ic drugs or Amiodarone)
-Ventricular paced rhythms 
SVT vs VT 
-The majority of patients with VT have structural heart disease, In SVT they may or may not have.
-Patient with VT are older.
-Patients with SVT more often have history of previous similar episodes .
-Overall appearance of patient is not accurate.
-The widespread impression that hemodynamic stability indicates SVT is erroneous and can lead to dangerous mistreatment.
-Physical findings that indicate presence of AV dissociation (cannon A waves, variable-intensity S1,variation in BP unrelated to respiration) if present are useful.
-Termination of WCT in response to maneuvers like Valsalva, carotid sinus pressure, or adenosine is strongly in-favor of SVT but there are well-documented cases of VT responsive to these.
-Diagnostic injection of verapamil or beta-blockers should be discouraged. (prolonged hypotension).
-QRS duration:70% of VTs have QRS duration more than140, but no SVT has it. VT is probable when QRS  more than 140 with RBBB and more than160 with LBBB pattern.Anti arrhythmic drugs may prolong QRS. Some patients with VT may have QRS of 120-140 specially in those without structural heart disease.
by
Akshaya Srikanth, Dr.S.Chandra Babu*
Pharm.D*, *Asso.Professor of Medicine
RIMS Medical College, Kadapa, A.P
INDIA