The Patient A 64-year-old woman has called 911 because she has chest discomfort radiating to her left arm, palpitations, weakness, and a headache. She had a valve replacement (we do not know which valve) two weeks ago and has a healing incision over her sternum. She is found sitting in a chair, pale, cool, and diaphoretic. Her blood pressure is 94/palp. Her pulse rate is 196 bpm and weak. She is afebrile.
ECG #1 This ECG shows a wide-complex tachycardia at 196 bpm. The QRS complexes are .132 seconds in duration, per the ECG machine. The rate is too fast to appreciate whether there are P waves present. We did not see the onset of the tachycardia, but with a rate this fast and regular, it is most likely a reentrant rhythm, rather than sinus tachycardia. An abrupt onset of the rhythm would point to a diagnosis of a reentrant rhythm, either ventricular tachycardia (VT) or paroxysmal supraventricular tachycardia (PSVT).
There is an important rule in emergency medical care: a wide-complex tachycardia should be treated as VT until and unless it is proven to be something else. The most likely alternate interpretation is PSVT with aberrant conduction, which usually takes the form of left or right bundle branch block. Fortunately, the paramedics on this call have a protocol for treating WCT that includes electrical cardioversion for the unstable patient, and amiodarone for the stable patient. This protocol serves both possibilities, VT and PSVT, well. The patient’s perfusion status and BP made her borderline in this determination, but she was alert and oriented, so the paramedics opted for administering the amiodarone while they prepared to electrically cardiovert.
An interesting finding of this ECG is that the pattern for LEFT BUNDLE BRANCH BLOCK is present. The criteria for LBBB is: supraventricular rhythm, wide QRS, negative QRS in V1 and positive QRS in Leads I and V6. Without visible P waves, we cannot prove that this is a supraventricular rhythm, but this looks like LBBB. There are ST changes that we normally associate with LBBB – discordant ST segments. That is, there is ST elevation in leads with negative QRS complexes and ST depression in leads with positive ST segments. For further information regarding evaluating ST segments for M.I. when there are discordant ST changes, I would refer you to Dr. Steven Smith’s, et al, modification of Sgarbossa’s Criteria.
ECG #2 Approximately 7 minutes later, the rhythm converted to sinus rhythm at 100 bpm. When the rate changed, P waves became quite obvious, and the QRS complexes did not change. She now has sinus rhythm with LEFT BUNDLE BRANCH BLOCK, proving that the faster rhythm was also LBBB, rather than VT. She also meets voltage criteria for left ventricular hypertrophy, which causes ST changes similar to those caused by LBBB. At the time of conversion, her BP became 130/P and her skin regained normal color and temperature, without diaphoresis. Her subjective symptoms improved. She was maintained on the Amiodarone drip for the short transport to the hospital. It is possible that this is a rate-dependent bundle branch block, as the sinus rate is around 100 bpm, and the rhythm would need to be reevaluated when she regains a slower rate.
This case is a good endorsement for initial treatment protocols for wide-complex tachycardia that are effective for both VT and PSVT.