Stem: This 74 year old man with a past history of renal carcinoma presentedwith central chest pain to a rural hospital. The initial ECG showed ST elevation in the inferior limb leads, and the serum troponin was elevated. The hospital did not have facilities for cardiac catheterization, and thrombolytic treatment was not given because of the history of cancer. The helicopter transfer of the patient to a tertiary hospital was delayed because of logistic problems and adverse weather. The ECG taken on arrival at the tertiary hospital was 12 hours after the onset of chest pain.
+ List the significant findings in the ECG and provide the most likely diagnosis
- The rhythm is regular. The ventricular rate is about 52 beats per minute
- The PR, QRS and QT intervals are normal. There is a leftward frontal plane QRS axis (of about - 23 degrees). The transition zone is between Lead V2 and V3
- Inverted P waves are seen before each QRS complex in the inferior leads, with a PR interval of about 160 msec. The P waves are upright in Lead aVR, and are inverted in Leads V3 to V6. The atrial rate is about 52 beats per minute
- The inverted P waves in the inferior leads, the normal QRS width and the atrial rate of 52 beats per minute are consistent with a junctional rhythm
- The limb lead changes are:
- Voltages consistent with left ventricular hypertrophy (RV1 + SIII = 14 + 13 = 27 mm [Sokolow and Lyon criteria are a value ≥ 25 mm]; R in Lead aVL = 14 mm [Sokolow and Lyon criteria are > 11 mm]
- Leads I and aVL have small Q waves and 2 mm of horizontal ST depression
- Lead aVR has slight (0.5 mm) ST elevation
- Lead II has a small amplitude complex with a small Q wave and a notched R wave.
- Lead III has a rS wave, the J point is elevated, and there is about 1.5 mm horizontal ST elevation that merges into a biphasic T wave
- Lead aVF has a deep Q wave, the J point is elevated, and there is about 1.0 mm horizontal ST elevation that merges into a biphasic T wave
- The changes in the inferior leads are consistent with a evolving inferior ST elevation myocardial infarct
- The praecordial lead changes are:
- Leads V2 and V3 have a tall R wave, 1 mm of horizontal ST depression and an upright T wave - these are the features of a posterior acute myocardial infarct (1).
- Leads V4 to V6 have small Q waves, a depressed J point and up-sloping ST depression
(1). The ST depression is caused by a ST injury vector moving away from Leads V2 and V3. Placing additional leads (V7 to V9 : V7 at posterior axillary line, even with tip of scapula; V9 paraspinal at same level; V8 between them)) on the back may detect ST elevation due to this ST injury vector.