Some patients have no significant blockage of their heart arteries upon testing, and yet continue to be troubled by symptoms typical of angina. Recent studies suggest that such signs shouldn’t be ignored.

Chest tightness or significant shortness of breath on exertion which is relieved on rest is termed as angina and suggests that one may have significant blockage of the heart artery. However, there are some with “angina” who have no significant blockage of the heart arteries upon testing, and yet continue to be troubled by symptoms typical of angina. Many doctors will dismiss it as “all in the mind” and deem the symptoms to be inconsequential. Based on data from recent research, this may not be so.

Heart attacks in the absence of significant disease

There is increasing evidence to show that angina and heart attacks do not only occur in patients with significant blockage of the coronary (heart) arteries. A study on a United States database of more than 400,000 patients undergoing invasive imaging of the heart arteries via the insertion of plastic tubes into arteries and the injection of contrast agents into heart arteries (coronary angiography) by Patel published in New England of Medicine Journal showed that of those suspected to have heart artery disease, only about one third had significant blockage of the heart arteries.

A January 2015 study by researchers from the University of Adelaide, Australia, analysed the current publications on those with Myocardial Infarction (heart attacks) with Non-Obstructive Coronary Artery disease (MINOCA) and showed that about 6%of patients with heart attacks have no evidence of significant blockage of the heart arteries. Compared to those with significant blockage of heart arteries, patients with MINOCA tend to be younger and are less likely to have high cholesterol levels.  The latest universal definition of myocardial infarction (heart attack), which represents the views of the major cardiology organisations in the world, recognises the mounting evidence that heart attacks do occur in the absence of significant blockage of the heart arteries.

Why angina occurs in the absence of significant heart disease

The results of research show us that those with angina but no evidence of significant blockage of heart arteries may not be “normal” after all.

A study led by researchers from Stanford University Medical Center published in Circulation journal in 2015 sought to understand the mechanisms that can explain the presence of angina in those without significant obstruction of the heart arteries. The study examined the physical and physiological properties of the heart arteries. The heart artery is not a fixed diameter cylindrical tubing but is a living structure which can constrict or dilate in response to stress, chemicals and drugs.

About three quarters of these patients with angina but no significant heart artery blockage were found to have abnormalities in their heart arteries including one or more of the following:- presence of plaque deposits in the walls of the arteries, abnormal physiological  function of the inner layer of the heart artery lining, reduced blood flow in the microscopic vessels of the heart and significant reduction of blood  flow in the heart arteries despite the absence of significant physical blockage of the heart arteries. The commonest abnormalities were abnormal physiological function of the inner lining of the heart artery and the presence of myocardial bridging.

Heart artery compression

Myocardial bridging is a condition in which the main heart arteries,  instead of being lying external to the heart muscle wall through its entire course , has one of its segments buried by heart muscle . In such a situation, whenever the heart muscle contracts, the muscle surrounding the buried segment of the heart artery will contract and reduce the size of the lumen.  Sometimes, when the artery is buried deeply into the heart muscle, the buried segment may almost be completely blocked during contraction of the heart. As muscle bridging of heart arteries is not uncommon and studies of patients with myocardial bridging have shown no long term adverse outcomes in study groups, one does not need to be alarmed about the presence of myocardial bridging. The exception will be those where myocardial bridging affects the main heart artery providing most of the blood supply to the left pumping chamber of the heart, and the affected heart artery segment is buried deeply into the heart muscle.

Abnormal “normal” arteries

In the Stanford led study, all the patients with abnormal physiological function of the heart arteries or reduced flow to the microscopic vessels of the heart were shown to have underlying deposits in the heart artery walls resulting in narrowing of the heart arteries which are not visually significant or obvious but detectable on ultrasound scanning of the heart arteries. What this means is that even if cholesterol deposits or damage to the arteries from diabetes mellitus do not cause significant obstruction to the heart arteries, they can cause abnormal function of the main heart arteries and/or disease of the microscopic vessels in the heart.  More than three quarters of these patients had an abnormal result on stress testing suggesting that the heart muscle may not be receiving sufficient blood flow. This group of patients are at a higher risk of developing an adverse heart outcome.

Of the close to one quarter of the patients in this study which did not have abnormalities of their heart arteries, they are expected to have good outcomes and only require reassurance.

Do not dismiss the chest pain

In practical terms, what the current data means is that for those with typical angina, even if there is no significant blockage of the heart arteries, it is very likely that the heart arteries have plaques and are abnormal. They are also at higher risk of getting a heart attack. Hence, if your doctor tells you that your arteries have minor disease and yet you continue to have recurrent chest pain, you will need to control your risk factors such as cholesterol, high blood pressure and diabetes mellitus well.

Last week, at a dinner with an old classmate, he related the recent incident where a male patient in his early forties with chest symptoms and multiple risk factors had a treadmill test done to screen for heart disease and he was told that the treadmill test did not show any significant abnormality. Two weeks later, the patient passed away of a sudden heart attack.

Most researchers believe that heart attacks occur in these patients as a result of a tear in the lining of the plaque triggering a series of biological reactions which culminate in the formation of a blood clot which occludes the lumen of the vessel.  Less commonly, spasm of the heart artery causes severe constriction of the heart artery resulting in a heart attack. Hence, recurrent chest pain symptoms typical of angina should not be dismissed as “all in the mind”.