A paramedic crew responded to the office of a local physician. A 61-year-old male presented with a one-week history of chest pain and shortness of breath. He had a previously undiagnosed atrial fibrillation with rapid ventricular response and left bundle branch block, but was alert. Shortly after transport commenced, the patient became unresponsive with Torsades de Pointes, which rapidly degenerated into ventricular fibrillation. The paramedic placed pads and defibrillated within one minute. After two minutes of compressions, the patient had a fairly regular rhythm with return of spontaneous circulation. Transport time was short. On catheterization, the patient was found to have severe coronary artery disease, requiring coronary artery bypass graft surgery (CABG) A balloon pump was inserted in an attempt to strengthen him for surgery.
What is the rhythm? The 12-lead ECG presented here shows atrial fibrillation at a rate of 138 per minute. The rhythm is irregularly-irregular with no P waves. Since the patient had not yet been diagnosed with atrial fib, obviously no therapy had been initiated to control the rate. There is a PVC near the end of the strip.
Why is the QRS complex wide? The QRS complex is wide at 0.168 sec (168 ms). It meets the ECG criteria for left bundle branch block (wide QRS, supraventricular rhythm, negative V1 and positive Leads I and V6). Atrial fibrillation can lower cardiac output because there is no P wave, and therefore, no “atrial kick”. Left BBB can lower cardiac output because a wide QRS is a sign of unsynchronized depolarization of the ventricular muscle, which causes less pumping force. To help you determine if a rhythm is LBBB or VT, review Brugada's Criterion.
Are there ST changes? In wide-complex rhythms, it can be difficult to determine whether acute M.I. is present, because the wide QRS is normally accompanied by “discordant ST changes”. That is, if the QRS is positive, the ST and T wave are negative. If the QRS is negative, the ST and T will be elevated. In this ECG, there is a subtle ST elevation in Leads III and aVR, and subtle ST depression in I and aVL. It is difficult to attribute this to A.M.I., but subsequent events point to that as the diagnosis.
What about the rhythm strips that follow? The rhythm strips provided show the patient’s quick progression, during transport to the hospital, from atrial fib with PVCs to Torsades de Pointes, to V Fib. They show an electrical shock at 200 joules approximately 1 minute after the VT started. This shock successfully converted the patient’s rhythm. First, it appears that the rhythm may be atrial flutter with 4:1 conduction (or it may be baseline artifact). By the final strip shown, we see a regular rhythm without clear P waves at a rate of 50 bpm. This could be a junctional rhythm, difficult to assess with only a 2-lead rhythm strip.
This series provides many teaching opportunities.
1) Both atrial fib with LBBB and VT can cause a WIDE-COMPLEX TACHYCARDIA.
2) It can be difficult to see the classic signs of STEMI when BBB is present.
3) VT can progress VERY RAPIDLY to V Fib, especially in low-output conditions.
4) Effective chest compressions and quick defibrillation will often result in conversion to an organized rhythm. Defibrillating the perfused heart is infinitely more effective that shocking a poorly-perfused heart. Kudos to this crew for a job well done.