Which of the following features on the ECG would establish the diagnosis of ventricular tachycardia (VT) for the following patient?
A 75-year-old man is admitted to the hospital for surgical repair of a hip fracture. Preoperative ECG shows his ventricular rate to be 120 beat/min, with a broad QRS complex (130 MS).
A. AV dissociation B. Presence of an initial positive deflection (r wave) in all precordial leads C. Time from the initial r wave to the nadir of the s wave less than 60 MS in the precordial leads D. QRS complex less than 130 MS
Av dissociation-key concept/objective: to understand ecg characteristics that suggest ventricular tachycardia although the qrs complex is usually narrow in svt, it may be broad (> 120 ms) in patients who have either bundle branch block or aberrant conduction. a number of ecg findings have been found to be very helpful in distinguishing svt with a broad qrs complex from vt. for example, av dissociation (i.e., independent atrial activity during tachycardia), fusion beats, or capture beats prove the presence of vt. unfortunately, av dissociation is not apparent in 80% to 85% of patients with rapid vt, because the p wave is obscured by the qrs complex and t waves. in this setting, morphologic criteria may be very helpful in distinguishing svt from vt. use of morphologic criteria begins with careful attention to the precordial leads. any of the following features in the precordial tracings will favor the diagnosis of vt: (1) concordance of all the precordial leads (i.e., all are positive or all are negative); (2) absence of an initial positive deflection (r wave) in all precordial leads (s wave; recall that in ecg nomenclature, upper-case letters denote dominance; small waves are designated by lower-case letters); (3) an r/s pattern is present, but the time from the initial r to the nadir of the s wave is greater than 100 ms; (4) presence of a right bundle branch pattern in lead v1, with an r greater than s or a qr pattern, where q indicates the initial negative deflection; (5) presence of a left bundle branch pattern in v1, with a broad r wave (> 30 ms) or an interval of greater than 70 ms from the onset of the r wave to the nadir of the s wave; (6) extreme left axis deviation; or (7) very broad qrs complexes (> 160 ms) in the absence of drug therapy.