Physiology
Cardiovascular
Regarding Einthoven's triangle, which of the following statements is CORRECT:
Answer:
The wave of depolarisation through the heart causes local currents in surrounding fluid which are detected at the body surface as small changes in voltage. This forms the basis of the ECG. The classical ECG records voltage between the left and right arm (lead I), the right arm and left leg (lead II) and the left arm and left leg (lead III). This is represented by Einthoven's triangle. The size of the voltage at any time depends on the quantity of muscle depolarisation and the direction in which the wave of depolarisation is travelling. Thus lead II normally shows the largest deflection during ventricular depolarisation, as the muscle mass is greatest and depolarisation travels from apex to base, more or less parallel to a line from the left hip to the right shoulder.Electrocardiogram (ECG)
Physiology / Cardiovascular / Cardiac Cycle
Last Updated: 26th July 2024
The wave of depolarisation through the heart causes local currents in surrounding fluid which are detected at the body surface as small changes in voltage. This forms the basis of the ECG.
The classical ECG records voltage between the right and left arm (lead I), the right arm and left leg (lead II) and the left arm and left leg (lead III). This is represented by Einthoven's triangle.
The size of the voltage at any time depends on the quantity of muscle depolarisation and the direction in which the wave of depolarisation is travelling. Thus lead II normally shows the largest deflection during ventricular depolarisation, as the muscle mass is greatest and depolarisation travels from apex to base, more or less parallel to a line from the left hip to the right shoulder.
Einthoven's Triangle. (Image by Npatchett (Own work) [CC BY-SA 4.0 , via Wikimedia Commons)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
