A 58-year-old man with hypertension presents with chest discomfort. ECG shows left axis deviation, increased QRS voltage (Sokolow-Lyon index >3.5 mV), and asymmetrical T-wave inversion in lateral leads. Which finding on repeat ECG 6 hours later would best distinguish acute coronary syndrome from chronic left ventricular hypertrophy?

Explanation

## Distinguishing ACS from Chronic LVH: The Role of Dynamic ECG Changes ### Clinical Context The patient presents with features suggestive of LVH (left axis deviation, increased QRS voltage, asymmetrical T-wave inversion). The key to distinguishing acute coronary syndrome (ACS) from chronic LVH is the **dynamic evolution** of ECG changes over time. ### Key Point **Key Point:** Dynamic ST-segment changes (elevation or progressive depression) that evolve over hours are pathognomonic for acute myocardial injury and are NOT seen in chronic LVH, which has static ECG findings. ### Comparison: Static vs. Dynamic ECG Changes | Aspect | Chronic LVH | Acute Coronary Syndrome | | --- | --- | --- | | **ST-segment** | Isoelectric or minimal depression | Elevation (STEMI) or dynamic depression (NSTEMI) | | **T-wave changes** | Asymmetrical, static strain pattern | Symmetrical, dynamic evolution | | **Q waves** | Absent (unless prior MI) | New pathological Q waves (late finding) | | **Serial ECGs** | Unchanged over hours/days | Progressive changes (ST→T evolution) | | **Reciprocal changes** | Absent | Present in transmural MI | | **Temporal evolution** | Stable over months/years | Acute onset and rapid progression | ### Why New ST-Elevation with Dynamic Changes is the Best Answer **High-Yield:** The development of NEW ST-segment elevation (or dynamic ST changes) on a repeat ECG 6 hours later is diagnostic of acute transmural myocardial injury. This is an acute, evolving process that does NOT occur in chronic LVH. **Clinical Pearl:** The **Pardee wave** (symmetrical T-wave inversion following ST elevation) and the **dynamic evolution** of ST and T changes over hours to days are hallmarks of acute MI and are never seen in stable LVH. ### Why Other Findings Are Misleading **Progressive T-wave inversion:** While T-wave changes do evolve in ACS, progressive deepening of T-waves alone can also occur in LVH strain and is less specific than ST-segment changes. T-wave inversion without ST elevation is less discriminatory. **Persistent left axis deviation and unchanged QRS voltage:** This would actually support the diagnosis of chronic LVH, not ACS. Static findings favor a chronic process. **New pathological Q waves:** Q waves are a late finding in MI (appearing over days to weeks) and would not be expected on a repeat ECG 6 hours later. Q waves also indicate transmural necrosis but are not the earliest or most dynamic discriminator. ### Mnemonic: STEMI Evolution **Mnemonic: STEMI = ST Elevation → T inversion → Q waves** - **S**T elevation (hyperacute/acute phase, hours) - **T**-wave inversion (evolves over hours to days) - **Q** waves (late finding, days to weeks) In chronic LVH: **No ST elevation, static T-wave inversion, no Q waves** [cite:Harrison 21e Ch 297]