Diagnosis of Heart Block
The gold standard for diagnosing heart blocks are the following two methods:
- Electrocardiography (ECG) is the most effective method of diagnosing sinoatrial block. First degree SA block, however, cannot be detected using this method, since the ECG strip does not show when the SA node fires.
o First degree SA block can only be detected using electrophysiology study, which requires a small wire to be placed against the sinoatrial node.
o Second degree SA block type I – during this type of SA block the R-R interval on ECG gradually gets smaller, while the P-R interval remains the same, until a full QRS segment is dropped.
o Second degree SA block type II – is similar to second degree SA block type I, with the only difference being that the R-R interval remains constant.
o Third degree SA block – this type of block is seen as the absence of P waves on the ECG. The heart rhythm during this condition is usually irregular and can either be normal or slow.
Holter monitor is a device that is used for continuous monitoring of the heart’s electrical activity. The Holter monitor is used for at least 24 hours and can be worn for as long as two weeks. This is a great tool for detecting arrhythmias that are not constant and appear from time to time. Special software is then used to decode the signal, since it would be too time consuming to decode such a long signal by hand. The automatic analysis provides the doctor with data on heart beat interval measurement, beat morphology, rhythm overview and heart rate variability.
If SA block is thought to be associated with toxins, drugs, or electrolytes, then the doctors should perform:
- Test to identify electrolyte, glucose, calcium and magnesium levels
- Thyroid functions tests – this includes evaluation of levels of thyroid-stimulating hormone, thyroxine, and triiodothyronine.
- Toxicological screening – can detect various drugs and substances within the blood or urine sample.
Unless there are specific indications, imaging techniques are rarely used.
