An extreme rightward axis (-90° to -180°) is often more suggestive of ventricular tachycardia.
A slight irregularity of the RR intervals, especially in the early stages before settling into a regular rhythm, can be suggestive of ventricular tachycardia.
The width of the QRS complex can also be useful for distinguishing supraventricular tachycardia from ventricular tachycardia. In general, a wide QRS complex > 140 ms suggests tachycardia; however, a QRS duration < 140 ms is not helpful for excluding ventricular tachycardia, because ventricular tachycardia is sometimes associated with a relatively narrow QRS complex.
If the degree of voltage change in the first 40 ms of the QRS complex is less than the degree of voltage change in the last 40 ms of the complex, this finding is suggestive of ventricular tachycardia.
Fusion occurs when a supraventricular impulse reaches the AV node simultaneously with a ventricular impulse. The resulting QRS complex has a hybrid morphology that is between a narrow atrial complex and a wide ventricular complex. Intermittent fusion beats during a wide-complex tachycardia indicate AV dissociation and, therefore, also indicate ventricular tachycardia.
A capture beat occurs when a supraventricular rhythm briefly conducts in a normal fashion, with a resultant normal QRS complex. The term "capture beat" implies that the normal conduction system has momentarily replaced the control of a ventricular focus; hence, ventricular tachycardia is present.
As mentioned, the patient in this case was diagnosed with ventricular tachycardia, and elective surgery for repairing the hernia was put on hold. An electrophysiology study was arranged after consultation with a cardiologist. An arrhythmogenic focus of myocardial irritability, which was thought to be caused by scar tissue from an unrecognized previous myocardial infarction, was identified during the study. The patient had an automatic internal cardiac defibrillator placed and, subsequently, his hernia was successfully repaired.
Medscape © 2017 WebMD, LLC
Any views expressed above are the author's own and do not necessarily reflect the views of WebMD or Medscape.
Cite this: Ryland P. Byrd, Ehab S. Kasasbeh, Jonathan W. Burress. An 80-Year-Old Man With Lightheadedness - Medscape - Dec 08, 2017.