ECG Basics


68 causes of T wave, ST segment abnormalities

How often do you see an ECG that is just a little off? Maybe the T wave is flat, oddly-shaped or inverted. Maybe the ST segment is coved, very minimally-depressed or shows some J point elevation.

These are referred to as non-specific T wave and ST segment changes on the ECG because they are simply not specifically signaling any medical condition. Here, we consider the potentially-underlying reasons for these annoying minimal ECG changes and explore various clinical situations that could cause T waves and ST segments to deviate from normal.

In some instances, T wave changes might suggest specific conditions, such as peaked T waves in hyperkalemia or symmetric T wave inversions during myocardial ischemia. But what about all the other T wave abnormalities, such as flat T waves, biphasic T waves or asymmetric T wave inversions?

Similarly, ST segment abnormalities on the ECG can sometimes be due to a specific cause, such as ST segment elevation myocardial infarction, pericarditis or myocardial ischemia. Other times, there are just subtle abnormalities.

Review the following ECG findings when the ST segment change or T wave change is actually indicative of a specific condition. These are very important not to misinterpret.

After reading the list below in entirety, you will completely understand why the T wave and ST segment changes mentioned above are sometimes called non-specific. Although some in their severe form have a more classic ECG appearance that could help pinpoint a diagnosis, every situation is different. A mild abnormality (i.e. mild hyperkalemia or a very small MI) may only show a mild ECG change and not a full-blown abnormal finding. When a finding may sometimes be classic, it is listed next to the cause.

  1. Hypokalemia (ST segment depression, T-wave flattening)
  2. Hyperkalemia (multiple possible changes; when severe, classic finding is peaked T waves)
  3. Hypomagnesemia (flat, wide T waves; results in prolonged QT)
  4. Hypermagnesemia (increased T-wave amplitude)
  5. Hypercalcemia (short T wave with shortened QT interval; “J wave” when severe)
  6. Hypocalcemia (flat, wide T waves; results in prolonged QT)
  7. Hyponatremia (non-ischemic ST segment elevation)
  8. Memory T-wave abnormality post-pacing
  9. Memory T-wave abnormality post-rate-dependent BBB
  10. ST-T wave abnormalities associated with a LAFB
  11. ST-T wave abnormalities associated with LPFB
  12. ST-T wave abnormalities associated with LBBB
  13. ST-T wave abnormalities associated with RBBB
  14. ST-T wave abnormalities associated with NSIVCD
  15. ST-T wave abnormalities associated with WPW
  16. ST-T wave abnormalities associated with paced beats
  17. ST-T wave abnormalities associated with PVCs
  18. Myocarditis
  19. Myocardial ischemia (classic is significant ST segment depression; when mild, may be just a non-specific change)
  20. Myocardial infarction (non-ST segment elevation MI)
  21. VERY early myocardial injury (classic is “hyperacute T waves”)
  22. Reciprocal ischemic changes
  23. Left ventricular aneurysm (classic is persistent ST segment elevation 6 weeks after MI)
  24. Coronary spasm
  25. Digoxin
  26. Quinidine
  27. Tricyclic antidepressants (T-wave changes; classic is QRS widening)
  28. Many medication overdoses (see the below example of a clonidine overdose; this case looked like hyperacute T waves)

  29. Atrial flutter (flutter waves overlapping T waves)
  30. Infiltrative cardiomyopathy
  31. Takotsubo cardiomyopathy
  32. Hypertrophic obstructive cardiomyopathy
  33. Apical hypertrophic cardiomyopathy
  34. Arrhythmogenic right ventricular dysplasia
  35. Brugada syndrome
  36. Long QT syndromes
  37. LVH with strain
  38. RVH with strain
  39. Stage 3 pericarditis (T waves flattened)
  40. Cocaine toxicity
  41. Cardiac tumor
  42. Loeffler’s endocarditis
  43. Hypothemia
  44. Mitral valve prolapse
  45. Pericardial effusion
  46. Pericardial abscess
  47. Subarachnoid hemorrhage (deep inverted T waves, QT prolonged as well)
  48. Subdural hematoma (deep inverted T waves, QT prolonged as well)
  49. Intracranial hemorrhage (deep inverted T waves, QT prolonged as well)
  50. Stroke (deep inverted T waves, QT prolonged as well)
  51. Post carotid endarterectomy (deep inverted T waves, QT prolonged as well)
  52. Hyperventilation (can cause ST depression)
  53. Limb lead reversal
  54. ECG lead misplacement
  55. Physiologic junctional depression (occurs with sinus tachycardia)
  56. Pseudo ST-depression (wandering baseline from artifact, poor skin-electrode contact)
  57. Heightened adrenergic state (pain, panic attack, etc...)
  58. Early repolarization
  59. Hypothyroidism
  60. Truncal vagotomy
  61. Hypopituitarism
  62. Gallbladder disease
  63. Adrenal insufficiency
  64. Pulmonary embolism
  65. Post-prandial
  66. Persistent juvenile T-wave pattern
  67. Left-sided pleural effusion
  68. Normal variant

Every time you see an ECG with a T wave or ST segment that is not normal, use this list to identify the possible causes. There are likely additional scenarios I did not think to mention here; please use the comment section to add to the list.

- by Steven Lome