Despite the different types of pacemaker, essentially they all have the same function - to detect and act as the hearts pacemaker if an abnormality in rhythm is detected.
There are specific abnormal heart rhythms that will require a pacemaker to be inserted - if the heart beat is too slow (bradycardia) or too fast (tachycardia), if there is a irregular heart rate, heart failure, or when the heart does not receive the normal signals sent out by the sinoatrial (SA) node.
This is termed heart block. Sometimes electrical impulses generated by the heart's normal pacemaker are not transmitted to the ventricles quickly enough. This is often referred to as a conduction abnormality. Heart failure can cause this, as well as some drugs and cardiac surgery. Heart block has various well defined stages with the last stage resulting in complete heart block. In this stage, no information from the heart's normal pacemaker reaches the ventricles.
Luckily, the ventricles have their own built in pacemaker, though this is insufficient in providing the amount of blood the body needs to function adequately. As a result, fainting is a common problem with this form of heart disease. Pacemakers therefore provide an adequate pulse rate when the heart's rate is abnormal.
There are 3 different types of pacemaker - single chamber, dual chamber and biventricular chamber. The implantation procedure is normally carried out under local anaesthetic in the cardiac cath lab.
The ECG, blood pressure and Oxygen level in the blood are all very closely monitored throughout. For the single chamber pacemaker, an electrode wire is inserted into a large vein, normally a vein near the shoulder. This wire is the guided under X-ray by a cardiologist into the right atria or ventricle of the heart.
Once positioned in the heart the wire is tested by the cardiac physiologist through an external device called a pacing system analyzer. This measures the amount of energy the heart muscle needs to cause it to contract, the size, in millivolts, of the hearts own electrical impulses and whether the electrode is in a satisfactory position for it to be connected to the implantable pacemaker. During the testing of the wire/s, the patient may be aware of their heart beating slightly faster than usual or palpitations.
The wire at the skin is then "tunneled" away from the insertion point, and a small pocket is made under the skin where it is attached to the actual pacemaker box. For a dual chamber pacemaker, the same technique is used but there are 2 leads. One lead is guided to the right atria and the other to the right ventricle. A biventricular pacemaker has 3 leads or electrodes that are guided into the right atria and right and left ventricle. Depending on the type of rhythm or severity of heart disease, the cardiologist will choose the most appropriate one.