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Introduction   

Heart disease is a common condition affecting many Americans and is the leading cause of death in the United States (1). Proper diagnosis and careful monitoring are an important part of the care of the millions of people affected by heart disease. This is where cardiac testing comes in.

Using proven and established testing methods, we can specifically diagnose cardiac diseases and quantify the level of severity. These tests help guide care for patients suffering from heart disease. But what tests do we use? How are they performed? And how do we as nurses interpret these tests? This course will answer all these questions and give you more confidence in caring for patients with cardiac conditions.

Types of Cardiac Tests

There are three main categories of cardiac testing: labs, imaging, and electrocardiography. Labs, as you know, involve drawing blood samples to measure specific biomarkers or components of the blood. Labs are a common and relatively easy test to perform at almost any facility. Imaging studies are often used in cardiac testing, the most common one being the echocardiogram. Imaging studies require special equipment, and providers trained in using the equipment, and involve more hands-on time to receive results.

Imaging studies range from non-invasive ultrasound to invasive catheter placement. Finally, there is the electrocardiogram. The electrocardiogram – usually referred to as an ECG or EKG – has been a staple of cardiac testing since its invention in 1901 (5). It is a non-invasive way to visualize electrical conduction through the heart and can be used to aid in diagnosing many conditions (5).

Indications for Testing

The main indication for performing these tests is cardiac symptoms. These include symptoms such as shortness of breath, chest pain or pressure, palpitations, difficulty breathing while lying down, and peripheral edema (3). A new heart murmur or crackles in the lungs may also warrant cardiac testing (4,7). These are the symptoms to watch for in both a new onset cardiac condition and the worsening of a pre-existing condition.

Several professional organizations collaborate to define when certain tests are warranted, including the American College of Cardiology (ACC), the American Society of Echocardiography (ASE), and the Society for Cardiovascular Angiography and Interventions (SCAI). When each test is warranted will be outlined when describing each of the tests.

Clinical Indicators

Aside from patient symptoms, some additional clinical indicators may trigger further testing. An abnormal electrocardiogram (ECG) almost always prompts more testing. If the ECG shows signs of ischemia, a troponin level and possibly a coronary angiogram are indicated (7). If there is a new arrhythmia, an echocardiogram is warranted (4). In many instances, clinical indicators are used in combination with patient symptoms to determine the appropriate test.

Elevated cholesterol levels in a patient with no symptoms might be treated with just dietary counseling, while a patient with elevated cholesterol who has chest pain while working in their garden requires more investigation. Because many of these tests are so interrelated and have results that inform each other they are often ordered and completed together as a series.

Tests

Let’s discuss the most common cardiac tests. Cardiac testing ranges from the all-too-familiar labs to ultrasound and even invasive catheter placement. These tests are usually conducted starting with the least invasive and moving on to the more invasive as necessary. We will discuss how each of these tests is performed, what measures it takes, and how that information is used.

Labs

Labs are often the first test done for cardiac disease. As you are aware, labs are obtained by venipuncture and sent to a laboratory to be analyzed. The most common lab studies for heart disease include brain natriuretic peptide (BNP), troponin, lipid panel, basic metabolic panel, and liver function tests. Brain natriuretic peptide is a hormone released by your body in response to stretching of the heart muscle (3).

This stretching typically occurs from an increased blood volume in the ventricles because of heart failure (3). This makes BNP a reliable test for acute heart failure (4). A meta-analysis found that BNP is the single best preoperative predictor for major cardiac events following surgery (12). A normal BNP level is <100pg/ml but is frequently elevated to very high levels (20,000+) in acute heart failure (9).

Troponin is the go-to test when a patient is having chest pain. Troponin is a component of many of the muscles in our body, but the lab test looks specifically for troponin released from heart muscle (3). There are 2 types of troponin tests: the classic troponin, with a normal value of <0.04ng/ml, and the newer high-sensitivity cardiac troponin, with a normal range <15ng/ml (7). Increased levels of cardiac troponin suggests that heart muscle is breaking down, most commonly from ischemia during a heart attack (7).

Troponin can be falsely elevated in patients with poor kidney function (7). To more accurately measure if there is ongoing damage to the heart, the troponin is often measured as a series with a baseline level and then a recheck at 2 hours and 6 hours (7). If the troponin is elevated and continues to rise higher, it is diagnostic of ongoing damage to the heart (7).

A lipid panel is used to measure cholesterol and triglyceride levels in the blood. The panel measures total cholesterol, low-density lipoprotein (LDL) cholesterol, high-density lipoprotein (HDL) cholesterol and triglyceride levels (6). The normal level for total cholesterol is less than 200, less than 130 for LDL, greater than 40 for HDL and less than 150 for triglycerides (6). If these levels are off, it indicates hyperlipidemia which has a strong correlation with coronary artery disease (3).

A basic metabolic panel may seem like a strange test to check for cardiac function. The reason for checking a basic metabolic panel is that cardiac disease and kidney disease often coincide. The kidney is responsible for controlling fluid balance in the body, and when the heart fails it leads to a backup and accumulation of fluid (3).

This extra workload on the kidney, coupled with the fact that the heart is pumping less blood to the kidney often leads to kidney failure (3). A basic metabolic panel is a common lab test to assess kidney function, which helps identify coexisting kidney disease. A creatinine >1.2mg/dL or BUN >20mg/dL on the BMP can indicate kidney failure (3).

Electrolyte imbalances on a basic metabolic panel are also important to monitor for patients with heart disease. A standard treatment for heart failure is diuretics, such as Lasix (furosemide). These diuretics tend to lower electrolyte levels as well – potassium in particular. Low potassium levels can be dangerous and lead to fatal arrhythmias, especially in patients with cardiac disease. As a reminder, the normal level for potassium is 3.5-5.2mmol/L (3). Low sodium levels on a basic metabolic panel can also indicate fluid overload in a patient with heart disease. Sodium levels are normally 135-145mmol/L (3).

Finally, liver function tests are often monitored in patients with heart failure. The liver receives approximately 25% of cardiac output, which makes it particularly sensitive to reduced heart function (3). Additionally, if the right ventricle of the heart fails to pump enough blood forward fluid often backs up into the portal system and causes liver congestion (3). For these reasons, liver function tests are important to monitor in patients with heart failure. Normal values for LFTs are: 8-48 U/L for aspartate transaminase (AST), 7-55 U/L for alanine transaminase (ALT) and 0.1-1.2mg/dL for bilirubin (3).

Thyroid function tests, especially thyroid stimulating hormone, are also sometimes performed for patients with heart disease. Thyroid hormone is like your body’s accelerator, and too much or too little can affect heart function (3). Too much thyroid hormone can lead to heart rhythm problems or interfere with medical therapy for heart failure (9). Because of this, thyroid stimulating hormone is checked in patients with heart rhythm disorders or heart failure (9).

Thyroid stimulating hormone is a hormone in the body that tells the thyroid gland to produce more of the thyroid hormones (3). Somewhat counterintuitively, high levels of thyroid stimulating hormone suggest low thyroid function. The body is producing more thyroid-stimulating hormones in response to a lack of thyroid hormones being released by the thyroid gland (3). The normal range for thyroid stimulating hormone (TSH) is 0.4-4m/L (3).

Echocardiogram

Probably the most common imaging study that most of us are familiar with is the echocardiogram. The echocardiogram is such an important and common test that it deserves its section. An echocardiogram or “echo” can be performed either transthoracic (through the chest wall) or transesophageal (through the esophagus). Transthoracic is most common, as it is less invasive and easier to perform (4).

A transthoracic echocardiogram is sometimes abbreviated as “TTE”. A transthoracic echo is performed by placing an ultrasound probe on the chest and visualizing the heart. Being able to directly visualize the heart offers a lot of information. It allows the provider to measure the ejection fraction (EF) of the heart. Ejection fraction is an important measurement that guides much of the care patients with cardiac disease receive.

The ejection fraction is calculated by measuring the volume of blood in the heart just before systole and just after systole; the difference between these numbers is then reported as a percentage of the starting volume (4). As a refresher, the normal ejection fraction is 55-65% (3). Whether or not the ejection fraction is reduced (≤40%) is a major decision point in the treatment that a patient receives (9).

Measuring the ejection fraction isn’t the only thing an echo is good for. Echo also allows visualization of the heart valves and is the gold standard for diagnosing valvular disease (4). The provider performing the echo can take specific measurements of the valve opening, pressures on each side of the valve and the amount of regurgitation. These measurements allow us to classify how severe a person’s valve disease is. The severity of valve disease dictates what treatment the patient receives.

For example, valve replacement or repair is the only true curative treatment for valve disease but requires open heart surgery (7). Open heart surgery has several risks and requires a long recovery period, so it is typically only performed for a person with moderate or severe valve disease (7). Performing an echo is also used to diagnose other structural diseases and cardiomyopathies (2). Abnormal movement of the walls of the heart on an echo can also indicate ischemia and heart attack (7).

A transesophageal echocardiogram involves placing an ultrasound probe inside a patient’s esophagus to visualize the heart. As you can imagine, this requires the person to be sedated and involves more risk than a transthoracic echo (4). Transesophageal echo – or TEE – does allow better visualization of the mitral and tricuspid valves and may be necessary in some instances (4). Transesophageal echo is also used to check for intracardiac thrombi in patients with atrial fibrillation or severe heart failure (9). A TEE also requires a provider to be specially trained in the technique for performing the exam (4).

Another special version of the echocardiogram is the stress echo, often referred to as just a “stress test”. With this test, the patient’s heart is evaluated with ultrasound at rest and while under stress. The “stress” can be either exercised or by giving the patient dobutamine, a positive inotrope that stimulates the heart (4). The stress test assesses if the heart responds normally to stress and can be used to diagnose conditions such as coronary artery disease.

A “positive” stress test usually indicates that there were ischemic changes in the heart, meaning that the heart cannot get enough blood supply to meet the demands of stress (4). A positive stress test leads to further investigation of heart disease and altering medical therapy to optimize the heart.

Imaging Studies

Cardiac computed tomography (CT) and magnetic resonance imaging (MRI) are also sometimes performed, typically when an echocardiogram does not provide enough information (8). A common CT scan for cardiac disease is the cardiac CTA, which uses contrast to assess the coronary arteries. CTA is less specific than a coronary angiogram done in the Cath lab but is also less invasive. Cardiac MRI is used only occasionally to diagnose specific conditions such as myocarditis or in preparation for cardiac surgery (4). Both of these imaging studies allow healthcare providers to visualize the heart – similar to an echo – but with higher quality images and the ability to produce 3D mapping (4).

A chest X-ray is another common imaging study used in heart disease. As you are probably aware, a chest x-ray involves placing an X-ray plate behind the patient’s chest and taking an image with an X-ray machine. Chest X-ray visualizes the size of the heart to check for enlargement and can check for pulmonary edema from heart failure (8). An enlarged heart suggests chronic heart failure and/or heart valve disease (4).

Among the most invasive cardiac tests are those performed in the cardiac catheterization lab, or Cath lab. One such procedure is the coronary angiogram, which involves inserting catheters into an artery and advancing it up to the heart to assess the coronary arteries (7). A coronary angiogram is the definitive test for an acute myocardial infarction and can be both diagnostic and therapeutic (7).

Coronary angiograms are not without risk and therefore are only recommended in symptomatic/unstable patients (4,7). Another invasive test is the right heart catheterization. A right heart Cath involves inserting a special catheter into the internal jugular vein and advancing it through the right side of the heart into the pulmonary artery (4). This allows the proceduralist to measure pressures inside the heart and pulmonary arteries to diagnose conditions such as pulmonary hypertension (4). These procedures require the provider to be specially trained in interventional cardiology to complete them (15).

Electrocardiogram

The electrocardiogram is a staple in the world of cardiology. It is a simple-to-perform, non-invasive test that can provide a plethora of useful information about a patient’s heart health. An electrocardiogram, or ECG, is performed by placing electrodes on a patient’s thorax which detects electrical changes in the heart (8).

For continuous monitoring, a 5-lead system is often used and for interval testing a 12-lead system is utilized (8). The 12-lead ECG can detect ischemia and heart rhythm changes and can give clues about other heart conditions such as ventricular hypertrophy (8). The ECG is used frequently because of the wealth of information it can provide, and because it is an easily performed test that produces immediate results.

Continuous ECG monitoring is recommended for 24-48 hours in patients with a myocardial infarction, or coronary angiogram with intervention (8). ECG monitoring should be done for 48-72 hours after open heart surgery and a minimum of 3 days for a transcatheter valve replacement (8). For patients presenting with an abnormal heart rhythm, such as atrial fibrillation or ventricular tachycardia, ECG monitoring should be continued until a definitive treatment strategy is in place (8).

Cardiac Conditions that Require Monitoring

Most common heart conditions require some form of monitoring. Valvular heart disease requires routine echocardiography, depending on the severity of the valve disease. An echocardiogram should be performed at least every 3-5 years for mild valve disease, every 1-2 years for moderate valve disease, and every six months to one year for severe valve disease (2). An ECG should also be performed for these patients at a similar interval to assess for changes in heart rhythm (8).

For patients with a new diagnosis of coronary artery disease, they should have an ECG, echocardiogram, and labs evaluated (7). These tests can identify other cardiac conditions that often co-occur with coronary artery disease, such as heart failure (7). Once the patient is stable on medical management, however, no routine testing is recommended (7). An echo, ECG and potentially a CTA or coronary angiogram are warranted when a patient remains symptomatic even with appropriate medical therapy (7).

Patients with newly diagnosed heart failure should all have an ECG completed, and the cause of their heart failure explored with tests such as an echocardiogram, labs, and potentially a coronary angiogram or right heart Cath (9). Also, CBC, BMP, liver function tests, thyroid-stimulating hormone, urinalysis, and iron studies should be completed (9).

Patients with worsening symptoms of heart failure should have a chest X-ray and echocardiogram performed to assess for changes and guide therapy (9). Cardiac CT or MRI scans may be necessary if other tests do not provide enough information about a symptomatic patient (9).

Special Considerations

There are some special considerations for cardiac testing. Firstly, we must assess how stable the patient is before performing any diagnostic testing. If a patient is hemodynamically unstable, it is not in their best interest to send them for an MRI. A potential exception to this is procedures such as coronary angiogram or right heart Cath where the test is both diagnostic and therapeutic. If you are caring for an unstable patient with a myocardial infarction, likely the best thing for them is to have a coronary angiogram to relieve the ischemia.

Secondly, we must consider how we can effectively perform the procedure. If you have a non-cooperative patient, performing many of these studies can be difficult. At times it may be necessary to offer some amount of sedation so that tests can be performed safely and effectively (4). Just always be sure to perform the appropriate level of monitoring when providing sedation, per your facility guidelines. Additionally, for cardiac imaging studies, such as cardiac CT or MRI, a heart rate of less than 90 is necessary to obtain accurate results (4). If the patient’s heart rate is elevated, they may need to be pre-medicated to lower their heart rate before the procedure can be completed.

Thirdly, we must consider the risks associated with the tests we are planning to perform. This is especially true of invasive testing, such as a coronary angiogram. Coronary angiograms have an overall complication rate of less than 1% but may result in serious complications including death (10). An important consideration for coronary angiograms and other imaging studies is the use of contrast dye. Contrast dye can cause acute kidney injury or worsening of renal function (10). For this reason, risks and benefits must be carefully weighed in patients with poor renal function.

Finally, pacemakers have a few special considerations related to cardiac tests. If the patient requires an MRI, the pacemaker must be assessed for MRI compatibility. Most modern pacemakers are MRI-compatible but require special programming before the MRI is completed (4). Also, if a person with a pacemaker needs an ECG completed, the pacemaker can be interrogated to receive an ECG (8).

Pacemaker interrogation is useful because it can provide an ECG from past events, rather than only giving the current electrical activity. A pacemaker interrogation does, however, require special equipment and staff trained on the equipment, so it may be easier to perform an ECG normally for real-time assessment.

Research Findings and the Future of Cardiac Testing

There are several exciting new developments in the world of cardiac testing. Artificial intelligence is now being combined with ECGs to provide even more information about patients. Artificial intelligence can predict a person’s likelihood of developing cardiac conditions such as atrial fibrillation or heart blocks (11). This may allow providers to be more proactive in caring for cardiac diseases. Another interesting finding from the research is that smartwatches can detect cardiac arrhythmias with an 85% or higher accuracy (13).

Smartwatches are ubiquitous in the modern age, and their accuracy in detecting arrhythmias holds a lot of potential for the future. There has also been a recent move towards telehealth. Research shows that some cardiac tests, such as the 6-minute walk test can be conducted effectively via telemedicine (14). The 6-minute walk test is exactly what it sounds like; it is a test that measures how far a person can walk in 6 minutes and what symptoms they experience (14). These recent developments in cardiac testing hold a lot of potential for new ways to assess our patients, even from a distance and perhaps even before a problem occurs.

Conclusion

Cardiac diseases are a common and deadly problem. To best treat these diseases and provide the level of care our patients deserve, cardiac testing is vital. Cardiac testing can take many forms and ranges from simple non-invasive tests to complex invasive procedures. Understanding the different forms of testing and what they measure will assist you in caring for cardiac patients. Knowing when tests are indicated is a vital part of correctly diagnosing problems and developing the right treatment plan. To help illustrate the importance of cardiac testing let’s look at a case study.

Case Study

You are working in an outpatient clinic when a middle-aged male patient presents with intermittent shortness of breath. His shortness of breath first started a couple of months ago and seems to be getting worse. The shortness of breath is worse when he is active, but lately, he has been having difficulty breathing when trying to sleep at night as well. Today, he is having shortness of breath with any amount of activity, even walking from across the room.

• What problem could be causing his shortness of breath?
• What tests would help diagnose the problem?

After speaking with the provider, you recommend the patient report to the hospital for testing immediately. At the hospital, he receives an ECG, echo, chest x-ray, and has lab work drawn. The ECG shows normal sinus rhythm with ST-segment depression. The echo shows an ejection fraction (EF) of 45% with regional wall motion abnormalities. The heart is also enlarged, and they have moderate mitral regurgitation. The chest x-ray shows small bilateral pleural effusions. The labs show a normal CBC and BMP, but elevated cholesterol, BNP, and troponin levels.

• With this information what problem do you think the patient is having?
• What would be the appropriate next step?

With this diagnostic information, the patient is diagnosed with a non-ST elevated myocardial infarction (NSTEMI). They are scheduled to have a coronary angiogram in the Cath lab. The procedure goes well but shows 90% occlusions in all 3 of the major coronary arteries. No intervention was performed during the case, but a cardiac surgery consult was placed.

The cardiac surgeon recommends coronary artery bypass grafting. Before he proceeds with surgery, however, he asks for a transesophageal echo (TEE) to better assess the mitral valve and check for intracardiac thrombi. The TEE shows that the mitral regurgitation is moderate, bordering on severe and there are no intracardiac clots. With this information, the surgeon plans to perform a coronary artery bypass and mitral valve repair.

• What tests were necessary to reach the final treatment plan?
• What testing will this patient need following discharge after surgery?

Hopefully seeing how a vague symptom can lead to open heart surgery helps solidify just how important cardiac testing is. Without these tests, there could be any number of reasons a person might be short of breath. The correct treatment plan can only be formulated with enough information from these vital tests. I hope you have learned something that can be useful to you in your practice. Thank you!

• What information from this course can you use in your daily practice?
• If you needed to find information on cardiac testing in the future, what would be a good resource?

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