Case. A 75-year-old male with a history of systolic congestive heart failure, hypertension, diabetes, hyperlipidemia, and chronic obstructive pulmonary disease presents with shortness of breath.
Answer. A quick look at this ECG demonstrates bradycardia with 3rd degree heart block, left bundle branch block, and concern for ST elevation.
Lhe first thing to notice is that there is no communication between the p-waves and the QRS complexes. Since the p waves march out in a regular pattern independently of the QRS complexes, this qualifies as 3rd degree heart block. Looking more closely, you can see that the QRS complexes demonstrate left bundle branch block morphology. The QRS beats are wide complex (greater than 120 ms), there is a large dominant S wave in lead V1, there are broad notched R waves in the lateral leads, and left axis deviation is present. Importantly, you also see that QRS beats and T waves are NOT concordant. This is normal in LBBB morphology and is called appropriate discordance. In the anterior leads, you may notice approximately 5 mm of ST elevation. However, in LBBB morphology, up to 5 mm of elevation is acceptable as long as the T wave and QRS complexes are (appropriately) discordant. In leads with QRS complex and T wave concordance, ST elevation greater than 1 mm may suggest ischemia. Because this patient is quite bradycardic, it is also tempting to suspect MI, particularly given the concern for ST elevation. However, it is also important to note that bradycardia usually occurs in the setting of an inferior wall MI as opposed to an anterior wall MI. There is no ST elevation in the inferior leads of this ECG to suggest inferior wall MI and, as stated previously, the ST elevation in the anterior leads is probably acceptable in the setting of appropriate discordance. A repeat ECG for dynamic changes would be advisable to look for progression to greater elevation. Beware that in this particular ECG the positive QRS complex followed by the positive T wave at the beginning of V2 are from different leads and do not indicate concordance.
- Complete or 3rd degree heart block is characterized by p waves and QRS complex that appear completely independently of each other.
- In LBBB morphology, you will usually see wide complex beats, left axis deviation, large dominant S wave in lead V1, and broad and or notched R waves in I, V5, V6, and aVL.
- LBBB morphology often demonstrates appropriate discordance in which QRS complexes and T waves are opposite each other. ST elevation up to 5 mm is normal in this scenario.
- Bradycardia from MI is usually caused by inferior wall MI and additional etiologies should be suspected if no ischemic changes are seen in leads II, II and aVF.