Dr Anees Thajudeen
The human heart beats approximately 72 times a minute, which is more than a hundred thousand times in a day. With each heart beat it pumps around 70ml of oxygen-rich blood into the body, and an equal amount of oxygen-poor blood into the lung. The muscles of the heart are designed to push the blood into the body with enough force to deliver the vital elixir of life to all parts of the body, including the brain―overcoming gravity and the resistance offered by the often hardened blood vessels. It is almost a miracle that this bag of muscle―the heart―performs the function for the entire life, while consuming only seven per cent of all the energy utilised by the body.
Controlling this amazing organ is the heart’s own nervous system―a specialised network of cells that have similarity to the brain cells (neurons). The specialised tissue in the heart is organised into nodes and conducts tracts that generate electrical signals for the muscle cells of the heart. The muscle pump function requires all the muscle cells to act at nearly the same time to generate the pumping force with great efficiency.
The heart’s conduction system can activate all heart muscle cells in less than 100 milliseconds (one-tenth of a second), and it controls how fast or slow the heart beats. As you can imagine, abnormalities in the conduction system―a heart rhythm disorder―can affect the blood flow to vital organs and cause various symptoms or even sudden death.
Sometimes there is abnormal neural control of the heart. A specialist will suspect this when an elderly person has a sudden loss of consciousness. After the checks, we would slightly massage his carotid arteries in the neck while monitoring his ECG and we would be able to detect a sudden pause in his heart activity. This is an abnormal neural reaction. It happens because a regulating centre located on the walls of the carotid artery has become very sensitive to pressure. When pressed, or stretched, it relays impulses to the heart to stop beating. The result is loss of blood flow to the brain causing loss of consciousness and injuries. Fortunately, this abnormal reaction is rare, though it is often unrecognised―and is easily treated by implanting a pacemaker. Sudden and transient loss of consciousness, called syncope, is a dangerous symptom. Sometimes the underlying cause is easily identified. Without proper evaluation it may be misdiagnosed as seizures. The greatest risk of misdiagnosis is that syncope could be a warning sign of sudden death.
The last two decades have seen tremendous progress in our understanding of how sudden death happens and in ways and means to prevent it. In nearly all cases, this involves helping the heart to maintain its normal rhythm, and devices to rapidly convert a dangerous heart rhythm before the malfunction results in irreversible damage to the brain or other vital organs as a result of loss of blood supply.
Take, for instance, a recently recognised genetic disease―Brugada syndrome. The signs of the disease can be identified in the usual ECG. The most interesting patient with Brugada syndrome I have seen is a professor in English who was referred for recurrent falls with loss of consciousness. A cardiologist had seen him. He suspected Brugada syndrome and advised further evaluation. But the patient failed to get evaluated for risk of sudden death. In due course he had a prolonged episode of dangerous ventricular fibrillation; luckily he was revived by a relative and brought to a good hospital. The professor survived, but the duration of cardiac arrest was enough to cause some permanent damage to his forebrain. He underwent implantation of a defibrillator―now we can be sure that another prolonged arrest will not happen. The device will detect the dangerous rhythm and ‘shock’ him out of it. He slowly returned to his profession but he was never the same perceptive and nuanced teacher he once was. He would need another intervention a year or so later. This time he came with complaints of multiple ‘shocks’ from the implanted device. The ‘shocks’ were not painful but it was distressing enough to get repeatedly jolted by the device for his dangerous rhythms. We had to find ways to stop these dangerous rhythms from coming. When the drugs failed, we did a percutaneous procedure. We mapped the surface of his ventricle using catheters, looking for abnormal currents called ‘late currents’ which set up ventricular fibrillation. We eliminated these ‘late currents’ using radio-frequency energy and got rid of the dangerous rhythms.
A slow heart rate or sudden pauses between heart beats is a frequent problem in the aged, rarely in the young. It may lead to permanent damage or death and usually causes dizziness, loss of balance and short episodes of loss of consciousness. A sudden fall may result in significant trauma to the skull or fractures in major bones. Less commonly, the heart beats regularly but conduction of current to the major pumping chamber of the heart is blocked. The consequent delayed activation of the ventricle (the chamber that generates the pressure to pump blood) can lead to a lazy and weakened function. Over months or years, this can lead to heart failure―a dangerous condition where the heart cannot pump enough blood to vital organs. Now, a cardiologist can tackle this problem with a special type of pacemaker where an extra wire is used to stimulate the lazy chamber from both sides and make the contraction early and synchronous. One of the early cases where we implanted the device is in a 50-year old businessman who had two previous admissions with breathlessness. Evaluation showed his weakened heart muscle function was the result of a block in the conducting channel that was to supply current to the left ventricle. The patient was on multiple drugs to drain extra fluids from his body. After implantation of the special pacemaker, his heart muscle function improved dramatically within months. We call such improvements as a super response, and this is not unusual. The patient was completely ‘cured’ of his problems and in due course we eliminated all but one medicine.
Today, the specialist uses various tests including MRIs and genetic tests to identify abnormal genes and structural heart disease which increases the risk of dangerous rhythm abnormalities. The purpose of treating these rhythm abnormalities varies, from curing a patient of palpitations (fast heart beats), preventing loss of consciousness and strokes, preventing sudden death and treating heart failure.
Without an understanding of what regulates the normal human heart rhythm many would be suffering from life-changing symptoms. We would have lost many lives unexpectedly and prematurely.
Dr Thajudeen is consultant, cardiology and electrophysiology, KIMS Health Hospital, Thiruvananthapuram.