Clinical Conditions that Affect the EKG Case Studies

Home » MEDCLIN530 » EKG » 12-Lead EKG Confidence » VII. The Nonischemic Disorders: EKG Changes Related to Drugs, Electrolyte Abnormalities, and Other Diseases » 20. Clinical Conditions that Affect the EKG » Clinical Conditions that Affect the EKG Case Studies
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Vice Chair, Pediatrics
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Table of Contents

Case 1: Low voltage: Pneumothorax

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A pneumothorax occurs when air seeps into the pleural space. The air interferes with the negative pressure in the pleural space and causes the lung to collapse. A pneumothorax can occur spontaneously (without any specific cause). It can also occur secondary to some form of chest trauma. The air in the pleural space pushes the heart away from the chest wall and, since air is a poor conductor of electricity, it makes the waveforms on the EKG smaller. Sinus tachycardia may be present and may indicate hemodynamic compromise, or chest pain, or anxiety.

Case 2: Low voltage: Pleural effusion

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A pleural effusion is another condition that causes smaller waveforms on the EKG. A pleural effusion is the term used for the buildup of fluid in the pleural space. The buildup of fluid in the pleural space is often associated with certain carcinomas, infection, congestive heart failure, or hemorrhage. In this instance, the fluid pushes the heart away from the chest wall and EKG leads. This is typically seen in a large left-sided pleural effusion.

Case 3: Low-voltage: Dextrocardia

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Dextrocardia is another condition that may produce low voltage waves on the EKG. Dextrocardia is a congenital condition in which the heart is reversed in the frontal view in a mirror image of normal. Dextrocardia is a congenital defect that places the heart on the right side of the chest instead of the left side. This opposite position puts a greater distance between the heart and the precordial (chest) leads.
The EKG shows decreased waveform voltages as the leads progress from lead V1 to V6. Since the leads were placed on the left side of the patient’s chest, lead V2 is farther from the heart than V1. V3 is further than V2, and so on. V6 is the farthest from the heart, and therefore has the lowest voltage of all. The P wave direction in the frontal plane points abnormally to the patient’s right side (+135 degrees) and confirms the diagnosis.

Case 4: Low voltage: Pericardial effusion

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A pericardial effusion is a condition in which the pericardial space fills with fluid, exudates, or blood. It is often the result of infection, trauma, carcinoma, hypothyroidism, or rheumatoid disease. The fluid in the pericardial space decreases the voltage that reaches the EKG leads, thereby producing smaller waveforms. Large or rapidly accumulating effusions can affect the hemodynamic status of the patient. Sinus tachycardia suggests hemodynamic compromise.

Case 5: Low voltage: Infiltrative cardiomyopathy

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Systemic diseases can affect the heart along with other parts of the body. Amyloid is a systemic disease that causes deposition of amyloid fibrils and causes thickening of the myocardium as measured by echo. Although the myocardial walls appear thickened, EKG shows low voltage (Figure 20.12) because the thickened walls are not muscle but amyloid filler. The combination of low voltage on EKG and left ventricular hypertrophy (LVH) on echo (particularly in a speckled pattern) suggests amyloid disease of the heart.

Case 6: EKG in pericarditis

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Inflammation of the pericardium can cause changes on the electrocardiogram that can mimic ischemia or infarction. A rapid look at this EKG (Figure 20.15) could give the impression that the ST segment is elevated above the baseline in lead II. An overly rapid interpretation of the EKG would describe the ST as elevated and pointing toward the inferior wall, consistent with transmural ischemia or infarction. However, after closer inspection, there is no ST segment elevation in the frontal plane. Rather it is an optical illusion caused by the presence of PT segment depression.
Now, look more carefully at the close-up of lead II, as shown in Figure 20.15. The true baseline (arbitrarily, by definition) runs through the end of the T wave to the beginning of the P wave. There is no elevation of the ST segment in this lead. There is actually depression of the segment between the end of the P wave and the beginning of the QRS complex. This is PR segment depression, which is seen in pericarditis.

Case 7: Postoperative patients: Sinus tachycardia

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When evaluating a patient with sinus tachycardia, the nurse or physician should assess the patient’s level of pain. Pain stimulates the sympathetic nervous system, which causes the heart rate to rise. Postoperative patients who are experiencing pain and patients maintained on mechanical ventilators and not adequately sedated often develop sinus tachycardia. Once the patient is properly medicated and made comfortable, the heart rate often returns to normal. Other complications of surgery include pneumothorax, hypovolemia, and pulmonary embolism.

Case 8: Effects of cancer on the EKG

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Malignant carcinomas and some cancer treatment modalities directly affect the heart and cause specific changes on the EKG.

Manifestations of malignant invasion of the heart:

  • Pericardial effusion (Figure 20.28).
  • Tamponade.
  • Increased heart size, heart failure, and new heart murmurs.
  • Radiation therapy can cause pericarditis.
  • Chemotherapy can cause systolic heart failure, acutely or chronically.
  • Hypercoagulable states can result in pulmonary embolism.
  • Metastatic disease may also cause significant electrolyte disturbances.
  • Obstructive or chemotherapy-induced renal failure may lead to hyperkalemia (Figure 20.29).
  • Cancer patients may become hypovolemic (Figure 20.30) due to nausea and vomiting or bleeding.
  • Metastatic spread to bone may be associated with hypercalcemia (Figure 20.31).
Subarachnoid hemorrhage has been classically associated with repolarization abnormalities on the EKG. Typical findings are deep symmetrically inverted T waves in the V leads, frequently associated with a long QT interval. Figure 20.32 demonstrates both of these. Possible drug and electrolyte causes of long QT, as well as cardiac ischemia or infarction, should also be considered.

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