MEDICAL MATTERS Dr Muiris HoustonThe recurrence of Tony Blair's heart difficulties has focused peoples' attention on cardiac rhythm problems. In a reminder of just how routine treatment for the condition can be, the British Prime Minister emerged following a two-hour procedure and, after a weekend's rest, headed off to Africa the following Monday.
He is not the only politician to have experienced a rhythm problem. Dick Cheney, the US vice-president, has also had cardiac difficulties, including a number of heart attacks. And some years back, James Major (son of former British PM John Major) who is in his 20s, needed to have a permanent cardiac pacemaker fitted after collapsing on a number of occasions.
Collapse is one of the more dramatic effects of cardiac arrhythmias; usually the symptoms are more subtle and it can, in fact, be difficult to diagnose the exact cause of the problem. We know that Tony Blair experienced tiredness and palpitations, the common presenting complaints when a rhythm problem develops. Often symptoms, which can also include shortness of breath, are intermittent with the heart resuming a normal beat between episodes.
The heart normally beats at between 60 and 100 beats per minute. Its rhythm is as regular as clockwork. But if the rate goes above 100 (called tachycardia) or below 60 (called bradycardia), symptoms will develop because the efficiency of the heart as a pumping unit deteriorates. Or the heart rate may be normal but its regularity is compromised - the pulse feels jerky or the person notices a "dropped" beat every so often.
Both the rate and the rhythm of the heart are controlled by a specialised piece of heart tissue called the sino-atrial (SA) node. Located in the wall dividing the upper chambers of the heart, it generates the electrical waves that make the heart beat. The signal travels down the heart wall along the atrio ventricular (AV) bundle to its lower chambers (ventricles) before spreading throughout the heart muscle.
The SA node can wear out, leading to a slow heart rhythm. Or if the AV bundle breaks down (referred to as heart block), a slow pulse will also occur. It is one of the main reasons why someone might need an artificial pacemaker.
This tiny device, which is implanted under local anaesthetic, is about 2 cm square. It contains a long-life lithium battery and electronic circuitry in a titanium cell. Pacemakers are placed below the collar bone, usually in the left shoulder for someone who is right-handed, but always on the non-dominant side so as not to interfere with arm movement.
Two separate wires are threaded through veins into the right side of the heart. One wire is lodged in the upper chamber and is designed to monitor the heart's natural pacemaker. When this fails, or falls below a pre-set rate, the second wire in the right ventricle kicks into action and ensures a regular beat continues. A pacemaker usually lasts for 10 years and is checked annually in a cardiac out-patient department.
Mr Blair has described his heart problem as a "flutter". In fact, there is a medical condition called atrial flutter, one of a number of abnormal heart rhythms originating in the upper chamber of the heart. The collective name for these arrhythmias is supraventricular tachycardia (SVT). They are caused by the electric impulse from the SA node choosing a different pathway through the ventricles.
When Mr Blair experienced the problem last year, he was treated by cardioversion, the application of an external electric shock to the heart. This seems to have worked until August, when his symptoms recurred. His cardiologist has now moved to the next rung on the treatment ladder. Cardiac ablation is a procedure designed to restore normal rhythm by destroying a small and carefully selected part of the heart that is causing the problem.
Also known as radio frequency ablation, the procedure involves inserting a thin catheter through a vein in the groin and threading it all the way up to the heart. At its tip is a small wire that delivers energy to destroy a selected part of the rhythm-conducting fibres in the heart muscle.
Cardio ablation has a success rate of 90 per cent. If, however, this does not solve Mr Blair's problems, another long-term solution would be to place an implantable cardioverter in his chest wall. Another procedure for another day!
Dr Muiris Houston is pleased to hear from readers at mhouston@irish-times.ie but regrets he cannot answer individual queries.