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cardiac stress test

Image: “Cardiac stress test, stock footage taken at Beaumont Hospital” by Blue0ctane. License: Public Domain


Measurement of Blood Pressure Using a Sphygmomanometer

Blood pressure

Image: “Blood Pressure 126/70 mmHg – Result of Measurement” by Julo. License: Public Domain

According to the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7), systolic pressure (which is the pressure during cardiac contraction) of less than 120 mmHg and diastolic pressure (which is the pressure during the relaxation of the heart) of less than 80 mmHg is considered as normal blood pressure.

An important condition is that the evaluation should be based on an average of two or more measurements and conducted at two or more different office visits. Hypertension is defined as systolic blood pressure  greater than 140 mmHg and diastolic blood pressure greater than 90 mm Hg under the same evaluation conditions. Prehypertension refers to the state between normal and hypertensive conditions, which is a significant risk factor for progression into hypertension in the future (systolic blood pressure between 120–139 mmHg and diastolic between 80–89 mmHg).

sphygmomanometer is the basic instrument absolutely essential for the measurement of blood pressure. It is economical, portable, and reliable in diagnosing and guiding the treatment of hypertension with further prognostic assessment.

According to the well-known Framingham heart study, in between systolic, diastolic and pulse pressure, systolic blood pressure initially followed by pulse pressure, is the most important prognostic marker for the prediction of risk factors for cardiovascular disease in patients greater than 60 years of age, whereas diastolic blood pressure is important in patients less than 50 years of age. The most common types of sphygmomanometer are Mercury and Aneroid. Currently, automated oscillometric BP measuring devices are used increasingly and gaining in popularity.

Before measuring the blood pressure of the patient using a sphygmomanometer, a set of precautions need to be followed for the effective interpretation of the results. The patient should be properly seated, and the appropriate cuff size in reference to the arm size of the patient should be used. The sphygmomanometer used should be appropriately calibrated. The proper sitting position should support the arms of the patient in which the blood pressure is measured, with the patient seated comfortably without crossing the legs. The bladder of the cuff used for the blood pressure measurement should be over the brachial artery.

There are three acceptable measurements of blood pressure.

Office-Based Blood Pressure Measurement

The blood pressure measured in a physician cabin is known as office-based blood pressure measurement.

Home-Based Blood Pressure Measurement

The measurement of blood pressure at home may attenuate white coat hypertension. The final blood pressure represents the average of blood pressure measured during a week with at least 7 to 14 data points (including a combination of both morning and evening blood pressure values.) According to the home-based assessment, hypertension is defined as blood pressure greater than, or equal to, 135/85 mmHg.

Ambulatory Blood Pressure Measurement

Ambulatory blood pressure measurement is the measurement of the blood pressure during continuous movement of the patient. In this method, the blood pressure is an average of the data collected during a particular time interval (usually 24 to 48 hours).

Within the specified time interval, the repeated measurements vary (usually every 15 minutes during the daytime and 30 to 60 minutes during sleep). According to the ambulatory blood pressure measurement, hypertension is defined as blood pressure (final average) greater than 130/80 mmHg.

Cardiac Stress Testing

As the name suggests, after inducing stress, the cardiac function is evaluated. The stress is generated by performing exercise or using a pharmacological agent (dobutamine or Dipyridamole). It is a valid test for the evaluation of coronary artery disease.

stress-ecg

Image: “Stress-ECG with ST-segment-depression (arrow) beginning at 100 W (column C)” by JHeuser. License: Public Domain CC BY-SA 3.0

The test, which is performed after inducing the stress, can be electrocardiogram, echocardiography or radionuclide imaging. A pretest probability scoring is recommended to evaluate the risk of cardiovascular disease, which in turn, is based upon multiple criteria such as gender and age. Cardiac stress testing is recommended only for individuals who fall under intermediate pretest probability, which is a method used to evaluate whether or not a stress test is required.

It should be borne in mind that serious complications such as sudden cardiac death or myocardial infarction can occur in 1 in 10,000 as a result of stress tests.

Principle

The normal heart is nourished by myocardial oxygen supply. Unless the blockage is severe or significant, it is not clinically symptomatic. However, during exercise performance, the symptoms are precipitated as the oxygen demand is increased. The symptom presentation can be diagnosed by ECG changes.

Contraindications

Absolute contraindications against stress tests include unstable angina pectoris, arrhythmia, heart failure, stenosis, which are uncontrolled and symptomatic, acute aortic dissection, acute myocardial infarction within 2 days, and acute pulmonary embolism.

Types of Exercise Testing

Motor-driven treadmill and the stationary cycle ergometer are the two most common types of exercise stress test. The testing is usually shifted from a lower to a higher workload, with the maximum duration of the test lasting for about 10 minutes for effective results. The endpoint is either a predetermined heart rate to be achieved or the manifestation of symptoms by the patients undergoing the test.

Bruce protocol is the common protocol, which is followed for exercise testing. It should be known that other testing protocols are available, such as the Naughton protocol for patients who present after myocardial infarction, and modified Bruce protocols for patients who are obese and with a sedentary lifestyle.

Electrocardiogram (ECG or EKG)

Placement of the precordial leads in electrocardiography

Image: “Placement of the Precordial Leads in Electrocardiography” by Mikael Häggström. License: Public Domain

The electrical activity in the heart originates in the sinoatrial node and progresses to the atrioventricular node. Finally, it enters the Purkinje fibers through the Bundle of His. The electrical activity can be recorded as an electrocardiogram with the help of 12 electrodes placed over the skin on the chest at specific scientifically predefined regions.

Several conditions are associated with characteristic ECG patterns such as ST elevation and depression in the case of myocardial infarction, and QT prolongation in case of torsades de pointes. Premature ventricular contraction (the time interval between R peaks is a multiple of R-R interval) and ventricular tachycardia (wide ventricular complexes) can be diagnosed based on the ECG pattern.

Cardiac conduction defects are attributed to abnormal conduction pathways. The various degrees (first, second, and third) of heart block can be diagnosed based on the characteristic ECG patterns such as a P wave preceding ventricular complex and intermittent skipping of the ventricular beat. In addition, cardiac conditions, electrolyte abnormalities like hypokalemia and hyperkalemia, can also be diagnosed based on ECG.

Electrocardiogram is economical and affordable even at the level of a Primary Health Center. In fact, a basic medical doctor, without any super specialty, can interpret the status of the cardiovascular system based on the ECG.

Echocardiogram (Heart Ultrasound)

3D echocardiogram of a heart viewed from the apex

Image: “GIF-animation showing a moving echocardiogram; a 3D-loop of a heart viewed from the apex, with the apical part of the ventricles removed and the mitral valve clearly visible. Due to missing data the leaflet of the tricuspid and aortic valve is not clearly visible, but the openings are. To the left are two standard two-dimensional views taken from the 3D dataset.” by Kjetil Lenes. License: CC BY-SA 3.0

Echocardiogram is based on the principle of ultrasound and facilitates the visualization of the chambers of the heart, along with the status of the heart valves.

Doppler Echocardiography

Doppler echocardiography is based on Doppler Effect. When a transmitted wave is reflected, based on the pattern of the reflected waves, the frequency, velocity and direction of the flow of obstacle can be determined.

There are three main types of Doppler evaluations: continuous, color flow and pulsed evaluation. In the case of continuous Doppler, there is a continuous transmission and reception in the transducer, which increases the risk of overlap. However, in the case of pulsed evaluation, despite continuous transmission, the region of transducer reception is defined by specific space, which facilitates the determination of low-velocity blood flow accurately.

The Doppler is not only used in diagnosing cardiac conditions, but also pathologies related to the blood vessels such as deep vein thrombosis. Doppler echocardiography facilitates the diagnosis of varicose veins, which occur because of incompetent valves communicating between the superficial and deep venous system.

In the case of the heart, Doppler echocardiography can be used to determine the pressure differences across the stenotic valve and between the various chambers.

Cardiac Biomarkers

Comparison of the cardiac marker

Image: “Comparison of the Cardiac Marker” by Peetz et al. License: Public Domain

Any injury to the cardiac cells disrupts the cell membrane, which leads to leakage of cellular constituents, such as troponin, lactate dehydrogenase, and myoglobin. These proteins act as effective biomarkers for the determination of the extent and prognosis of cardiac injury in case of myocardial infarction and other conditions.

The normal physiological functions of troponin include calcium-mediated interactions with actin and myosin, which are contractile elements present in the cardiac cell. There are two types of troponin, namely troponin I and troponin T. The troponin test should be performed at the time of admission, followed by a second assay after 3 to 6 hours. A second assay should demonstrate at least a 20% increase compared with the level determined during the time of admission.

Some of the recent recommendations propose the use of troponin I and troponin T when compared with creatine kinase MB. Cardiac troponin is also better and more predictable when compared with lactate dehydrogenase, myoglobin, and other biomarkers used in the past.

Invasive Coronary Angiography

Coronary Angiography

Image: “Coronary Angiography” by BruceBlaus. License: Public Domain CC BY-SA 4.0

Invasive coronary angiography is the gold standard test for the visualization of the status of the heart vessels in coronary artery disease. Despite its comparative advantages over other tests, it is an expensive and invasive procedure. It does not provide insight into the functional status of the heart and the blocks in microcirculation.

Electrophysiology Study (EP Study)

Electrophysiology studies are used for the diagnosis and evaluation of the cardiac rhythm disorders. This test is highly invasive in nature with multipolar electrodes placed in various positions of heart such as right atrium and right ventricle classically. In addition, electrodes are also placed in positions such as coronary sinus, and bundle of His.

Advanced Radiological Techniques

Computed Tomography Coronary Angiography (CTCA)

Computed Tomography Coronary Angiography (CTCA) is based on the principles of coronary angiography, combined with computed tomography for visualization.

Multi-Detector Cardiac Computed Tomography (MDCT) and Magnetic Resonance (MR)

MDCT/MR imaging is non-invasive, and mainly used as research tools. However, it is used increasingly in clinical practice.

Criteria for Ordering Tests

  1. Never order a test where the results will not affect patient care decisions.
  2. Do not order two tests that yield the same result. A patient with suspected angina does not need an exercise nuclear test as well as a dobutamine stress echocardiogram.
  3. Always order the simplest of two forms of an imaging test first. If you can get the information you need for an exercise ECG test, do not order an expensive nuclear stress test as well, unless additional information is needed, for example, equivocal ECG results.
  4. Before ordering a stress test, review the history, physical examination, and ECG. The patient with a recent invasive coronary angiogram does not need a CT coronary angiogram.
  5. Always think before you order a test: What questions are you asking? What information do you want from the test? If you are ordering a CT angiogram to rule out coronary arterial atherosclerosis, do you really need the CT angiogram if a recent nuclear stress test was completely normal?
  6. A transthoracic echo study can help rule out a STEMI or a large NSTEMI in a patient with an abnormal ECG. For example, a 40-year-old diabetic male visits the ER complaining of chest discomfort. His ECG shows atypical ST elevations in a number of leads. His echo shows normal LV wall motion. This patient has not had an MI of considerable size, for example, a STEMI. However, you have not completely ruled out unstable angina or a small NSTEMI.
  7. What is the best stress test to diagnose ischemic heart disease? An exercise stress ECG test, an exercise nuclear stress test, a pharmacological nuclear stress test (dipyridamole, adenosine), an exercise echo stress test or a pharmacological echo stress test (dobutamine)? Imaging (echo and nuclear) stress tests are associated with fewer false negatives and false positives compared with ECG test alone. CT angiogram is most helpful if it is normal. However, CT, echo, and nuclear tests are more expensive.
  8. The selected test depends on the patient´s age and gender, baseline ECG, and the patient´s ability to exercise, presenting history, and the best test available in your location.
  9. How useful is a CT coronary artery calcium imaging test? This test is good but does not offer a perfect predictive value for CAD diagnosis. It is most useful in patients with an intermediate (not high and not low) risk for CAD. It is not useful in the elderly or in patients with a known diagnosis of CAD.
  10. A positive test result does not always establish a diagnosis. Test results can be erroneous although they are usually accurate. Always interpret the test result in light of the clinical situation.
  11. Which test to order depends on some degree of clinical expertise and experience of the person conducting and interpreting the test. It varies across different hospitals and should be investigated at your hospital.

 

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