In Australia recently, the deaths of three high profile people, two in their early 50s, shocked the nation and brought home the realities of heart disease and heart attack. Even though cardiovascular disease is the leading cause of death globally, perceptions remain that it is an older person’s disease, and that these people are obviously unhealthy. The reality is that in Australia, heart attack afflicts 57,000 people every year, and claims on average 21 lives each day.
The anatomy and physiology of the heart
You may notice your heartbeat from time to time, but have you pondered how it works and how much it works? The myocardium, the muscle of the heart, contracts an average of 60 – 80 times a minute, 100,000 to 130,000 times per day, and in a lifetime, anywhere from 2 – 3 billion beats.
The myocardial muscle fibres contract without conscious thought, the action orderly, coordinated, and synchronised by a precise electrical circuit. The result, an efficient pump of 80ml per beat and an average of 7,000 – 8,000 litres of blood per day. The main workhorse is the left ventricle, the bottom left of the four-chamber heart. Its job is to pump blood around the body for your working muscles and organs.
As we move, think or digest, our heart rate increases to accommodate the body’s increased metabolic demands. Likewise, as the heart rate increases, the oxygen and nutrients required by the heart increase.
Your heart needs blood too!
The heart typically has two main arteries supplying blood to the heart muscle and other heart structures. The right coronary artery supplies blood to the right atrium, right ventricle, the septum and the electrical circuitry of the heart on the right side (sinoatrial node and atrioventricular node). The left side predominately supplies the left atrium and left ventricle.
If blood flow through the coronary arteries is reduced, ischemia (oxygen deficiency) in the myocardium will result. The myocardium has a limited ability to compensate for reduced blood flow and will resort to inefficient use of fuel sources to continue myocardial contractions.
Like any muscle injury, an individual may feel this as (chest) pain, specifically heaviness in the chest or a compressed feeling (angina). This feeling of discomfort can spread to the arms, jaw, neck or back. Other symptoms may include dizziness, feeling faint, nausea, indigestion, vomiting, shortness of breath and sweating. Individuals may have any combination of the symptoms or no symptoms at all, despite their myocardium screaming for oxygen and nutrient-rich blood (silent ischemia). If the oxygen demand decreases and the myocardium’s supply of oxygen meets the demand the symptoms will diminish.
This then is a challenge for the medical professional: How do we get patients to seek medical attention promptly for the symptoms of a heart attack when these vary, or there are no symptoms at all? Patients themselves often try to rationalise the symptoms as indigestion, a “tweak” in the chest muscles or sternum and often “I’m just a little stressed, tired, worn-out”.
Self-diagnosing a heart attack is difficult given the range of symptoms that may be experienced
Anatomy of a Heart Attack
An occlusion (blockage) of the coronary arteries leads to the myocardium being without the critical oxygen it needs to not only function, but also to survive. If the occlusion is large enough and goes on for long enough, a myocardial infarct (a heart attack) results. It is now all about time as the heart muscle has limited time to re-establish blood flow before the cardiac muscle fibres are permanently damaged. Medical intervention is typically required in the form of drugs like thrombolytics (clot busters) and interventions such as the insertion of a stent to open the blockage and restore the blood flow. The longer it takes to receive treatment, the greater the area of myocardial tissue that may be permanently damaged.
Occluded artery leading to myocardial damage (dark area)
The irreversible damage of the myocardium takes on 4 main pathways:
Ischemia – The loss of nutrients and oxygen for prolonged periods will lead to heart muscle death.
Mechanical forces – The heart must keep beating to keep the rest of the body alive. The oxygen deprived heart muscle no longer contracts in unison with the remaining viable myocardial tissue. With each beat the ischemic myocardial fibres are placed under tension, traction and stretching. Higher heart rates place the ischemic myocardial fibres under increased stress. In extreme cases, the forces placed on the ischemic tissue can result in a complete rupture of the ventricular wall and immediate death.
Inflammation – Injured areas of the body undergo an inflammatory response, and the heart is no different. In the myocardium, the initial inflammation used to remove dead and damaged cells can lead to further myocardial damage before the anti-inflammatory response occurs.
Reperfusion injury – With a steep increase in oxygen at reperfusion, a proinflammatory response is seen which may lead to further myocardial damage. The damage may also extend to the capillary vessels supplying the ischemic myocardium. Cardiologists restoring blood flow follow a protocol to minimise reperfusion injury.
It’s about time
Time to damage is difficult to quantify, however it is established that there is a 2-hour time frame imperative for intervention and successful reperfusion to minimise damage. Innovative strategies such as giving thrombolytics to patients via trained paramedics has helped to preserve the myocardium. Further strategies like public awareness campaigns focused on symptoms of a heart attack try to reduce the time it takes for patients to seek medical intervention.
The consequence of a heart attack can be severe if not fatal. Those that survive are at a greater risk of a subsequent heart attack while the risk of heart failure, arrythmias and valvular regurgitation is also increased. In addition, psychosocial issues arise from the trauma of a heart attack that will impact ongoing quality of life.
It can start early
Coronary artery disease, often the precursor to myocardial infarcts, is a build-up of fat, cholesterol, and other materials. The coronary arteries may stiffen and/or narrow. If the coronary artery wall ruptures, a blood clot may form leading to angina or worse, a heart attack.
Based on the results from these tests, physicians will ask patients to make lifestyle changes and may prescribe medications that will help reduce the risk of a heart attack or damage to the heart. A formalised cardiac rehabilitation program may also be recommended for patients.
Patients deemed to be at high risk may have preventative intervention such as angioplasty, stents or a Coronary Artery Bypass Graft (CABG) surgery.
For those that have had a myocardial infarction or revascularisation procedure, secondary prevention by comprehensive risk factor modification is an ideal process to reduce mortality, decrease subsequent cardiac events, and improve quality of life. Secondary prevention maintains lifestyle modifications, medications, and cardiac rehabilitation with an increased surveillance on progression of heart disease including coronary artery disease, stroke, and heart failure.
To diagnose coronary artery disease before or during a heart attack, physicians may investigate with the following tests:
Coronary Computed Tomography Angiogram (CCTA)
Myocardial Perfusion Study (MPS)
Computerised Tomography scan (CT scan)
Preserving your Myocardium
Preserving your myocardium is a life-long goal for every individual. The billions of beats, pumping millions of litres of blood allows us to lead a full life, and we need our hearts to last longer as life expectancy increases.
The best way to preserve your myocardium is to not wait for a problem to appear. Start your heart health checks immediately. Make an appointment with your health professional now, and make heart health part of your regular routine.
About the Author:
Andrew Screech is Cardiology Product Manager at Hydrix Medical. He holds a Bachelor of Applied Science in Exercise Physiology and a Masters Degree in Cardiopulmonary Rehabilitation
About Hydrix Medical
Hydrix is a distributor of the GUARDIAN®, the world’s first FDA approved implanted heart attack detection and alerting technology. Developed for people who are at risk of a second heart attack, the GUARDIAN constantly monitors the heart and alerts the patient to see a doctor when a heart attack is detected, even in the absence of ‘typical’ heart attack symptoms.
The worlds first and only (FDA approved) implantable cardiac monitor with ACS detection technology