Pathological R-wave progression
Normal R-wave progression implies that the R-wave amplitude increases gradually from V1 to V5 and then diminishes again in V6. Refer to Figure 26 (below). Abnormal R-wave progression implies that the gradual increase from V1 to V5 is absent. It may be broken, as in Figure 26. Any type of infarction may cause pathological R-wave progression. However, the specificity for pathological R-wave progression is considerably lower than pathological Q-waves and guidelines do not state any ECG criteria specific to R-wave progression.
New U-waves (in absence of bradycardia) may indicate ischemia. If U-waves were present on previous recording, the amplitude must be increased in order to suggest ischemia. Inverted U-waves are even more typical of ischemia (but the sensitivity is low). U-wave changes always accompany other ischemic ST-T changes. They may occur in both NSTEMI and STEMI.
The QT (QTc) interval may be prolonged, shortened or unchanged in ischemia.
Acute transmural ischemia may transiently increase the amplitude of the R-waves. This is believed to be due to delayed (and thus electrically unopposed) depolarization in the ischemic area.
Fragmented QRS complex
The definition of fragmented QRS complexes are as follows:
- QRS complex with more than 1 R wave and/or
- notch in the descending limb of the R-wave and/or
- notch in the descending limb of the S-wave
In case of complete/incomplete bundle branch block or pacemaker rhythm, >2 notches are required in the S-wave or R-wave.
Fragmented QRS complexes are indications of previous myocardial infarction. There are imaging studies demonstrating that QRS fragmentation is more common than development of pathological Q-waves after infarction. The sensitivity of fragmented QRS for myocardial infarction was 86%, as compared with 36% for pathological Q-waves. However, the specificity was lower for fragmented QRS (89% vs 99%). Absence of fragmented QRS has a high negative predictive value (93%) for myocardial infarction. Moreover, fragmented QRS is associated with increased risk of sudden cardiac death and ventricular arrhythmias.