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Cardiology

ELECTROCARDIOGRAPHY (ECG OR EKG)

ECG is the process of recording the electrical activity of the heart over a short period of time using electrodes placed on the skin. These electrodes detect the tiny electrical changes on the skin that arise from the heart muscle's electrophysiologic pattern of depolarization and repolarization during each heartbeat. It is very commonly performed to detect any cardiac problems.

In a conventional 12-lead ECG, four electrodes are placed on the patient's limbs and six electrodes on the chest wall. The overall magnitude of the heart's electrical potential is then measured from twelve different angles ("leads") and is recorded over a period of time (usually ten seconds). In this way, the overall magnitude and direction of the heart's electrical depolarization is captured at each moment throughout the cardiac cycle. The graph of voltage versus time produced by this noninvasive medical procedure is an electrocardiogram.

During each heartbeat, a healthy heart has an orderly progression of depolarization that starts with pacemaker cells in the sinoatrial node, spreads out through the atrium, passes through the atrioventricular node down into the bundle of His and Purkinje fibers, spreading down and to the left throughout the ventricles. This orderly pattern of depolarization gives rise to the characteristic ECG tracing. To the trained clinician, an ECG conveys a large amount of information about the diseases of the structure of the heart and the function of its electrical conduction system. Among other things, an ECG can be used to measure the rate and rhythm of heartbeats, the size and position of the heart chambers, the presence of any damage to the heart's muscle cells or conduction system, the effects of cardiac drugs, and the function of implanted pacemakers.

MEDICAL USES OF ECG:

The overall goal of performing electrocardiography is to obtain information about the structure and function of the heart. Medical uses for this information are varied and generally relate to having a need for knowledge of the structure and/or function. Some indications for performing electrocardiography include:
  • Suspected myocardial infarction (heart attack) or chest pain
  • Suspected pulmonary embolism or shortness of breath
  • A third heart sound, fourth heart sound, a cardiac murmur or other findings to suggest structural heart disease
  • Perceived arrhythmia either by pulse or palpitations
  • Monitoring of known cardiac dysrhythmias
  • Fainting or collapse
  • Seizures
  • Monitoring the effects of a heart medication (e.g. drug-induced QT prolongation)
  • Assessing severity of electrolyte abnormalities, such as hyperkalemia
  • Hypertrophic cardiomyopathy screening in adolescents as part of sports medicine to avoid sudden cardiac death (varies by country)
  • Perioperative monitoring in which any form of anesthesia is involved (e.g. monitored anesthesia care, general anesthesia); typically preoperative, intraoperative and postoperative
  • As a part of a pre-operative assessment some time before a surgical procedure (especially for those with known cardiovascular disease or who are undergoing invasive or cardiac, vascular or pulmonary procedures, or who will receive general anesthesia)
  • Cardiac stress testing
  • Computed Tomography Angiography (CTA) and Magnetic Resonance Angiography (MRA) of the heart (ECG is used to "gate" the scanning so that the anatomical position of the heart is steady).

ECHOCARDIOGRAPHY

An Echocardiogram, often referred to as a cardiac echo or simply an echo, is a sonogram of the heart. (It is not abbreviated as ECG, because that is an abbreviation for an electrocardiogram.) Echocardiography uses standard two-dimensional, three-dimensional, and Doppler ultrasound to create images of the heart.

Echocardiography has become routinely used in the diagnosis, management, and follow-up of patients with any suspected or known heart diseases. It is one of the most widely used diagnostic tests in cardiology. It can provide a wealth of helpful information, including the size and shape of the heart (internal chamber size quantification), pumping capacity, and the location and extent of any tissue damage. An echocardiogram can also give physicians other estimates of heart function, such as a calculation of the cardiac output, ejection fraction, and diastolic function (how well the heart relaxes).

Echocardiography can help detect cardiomyopathies, such as hypertrophic cardiomyopathy, dilated cardiomyopathy, and many others. The use of stress echocardiography may also help determine whether any chest pain or associated symptoms are related to heart disease. The biggest advantage of transthoracic echocardiography is that it is not invasive (does not involve breaking the skin or entering body cavities) and has no known risks or side effects.

Not only can an echocardiogram create ultrasound images of heart structures, but, it can also produce accurate assessment of the blood flowing through the heart by Doppler echocardiography, using pulsed-or continuous-wave Doppler ultrasound. This allows assessment of both normal and abnormal blood flow through the heart. Color Doppler, as well as spectral Doppler, is used to visualize any abnormal communications between the left and right sides of the heart, any leaking of blood through the valves (valvular regurgitation), and estimate how well the valves open (or do not open in the case of valvular stenosis). The Doppler technique can also be used for tissue motion and velocity measurement, by tissue Doppler echocardiography.

Echocardiography was also the first ultrasound subspecialty to use intravenous contrast. Echocardiography is performed by cardiac sonographers, cardiac physiologists, or physicians trained in echocardiography.

MEDICAL USES

Health societies recommend the use of echocardiography for initial diagnosis when a change in the patient's clinical status occurs and when new data from an echocardiogram would result in the physician changing the patient's care. Health societies do not recommend routine testing when the patient has no change in clinical status or when a physician is unlikely to change care for the patient based on the results of testing.

A common example of overuse of echocardiography when not indicated is the use of routine testing in response to a patient diagnosis of mild valvular heart disease. In this case, patients are often asymptomatic for years before the onset of deterioration and the results of the echocardiogram would not result in a change in care without other change in clinical status.

TRANSTHORACIC ECHOCARDIOGRAM

A standard echocardiogram is also known as a transthoracic echocardiogram, or cardiac ultrasound. In this case, a transducer (or probe) is placed on the chest wall (or thorax) of the subject, and images are taken through the chest wall. This is a noninvasive, highly accurate, and quick assessment of the overall health of the heart.

TRANSESOPHAGEAL ECHOCARDIOGRAM (TEE)

This is an invasive way to perform an echocardiogram. A specialized long, flexible probe containing an ultrasound transducer at its tip is passed into the patient's esophagus. This allows image and Doppler evaluation from a location directly behind the heart. This is known as a transesophageal echocardiogram. Transesophageal echocardiograms are most often used when transthoracic images are suboptimal and when a more clear and precise image is needed for assessment to assess pathologies involving specially the base of the heart. This test is performed in the presence of a cardiologist, with the assistance of a registered nurse, and an ultrasound technician. Transesophageal Echocardiogram (TEE) is also useful in properly guiding the interventional cardiologists for different interventions and the Cardiothoracic surgeons during the cardiac surgeries. Conscious sedation and/or localized numbing medication may be used to make the patient more comfortable during the procedure.

THREE-DIMENSIONAL ECHOCARDIOGRAPHY

Three-dimensional echocardiography (also known as four-dimensional echocardiography when the picture is moving) is possible, using a matrix array ultrasound probe and an appropriate processing system. This enables detailed anatomical assessment of cardiac pathology, particularly valvular defects, and cardiomyopathies. The ability to slice the virtual heart in infinite planes in an anatomically appropriate manner and to reconstruct three-dimensional images of anatomic structures make it unique for the understanding of the congenitally malformed heart. Real - time three - dimensional echocardiography can be used to guide the location of bioptomes during the right ventricular endomyocardial biopsies, placement of catheter-delivered valvular devices, and in many other intraoperative assessments.

Three-dimensional echocardiography technology may feature anatomical intelligence, or the use of organ-modeling technology, to automatically identify anatomy based on generic models. All generic models refer to a data set of anatomical information that uniquely adapts to the variability in patient anatomy to perform specific tasks. Built on feature recognition and segmentation algorithms, this technology can provide patient-specific three-dimensional modeling of the heart and other aspects of the anatomy, including the brain, lungs, liver, kidneys, rib cage, and vertebral column.

CONTRAST ECHOCARDIOGRAPHY

Contrast echocardiography, or contrast-enhanced ultrasound is the addition of an ultrasound contrast medium, or imaging agent, to traditional ultrasonography. The ultrasound contrast is made up of tiny microbubbles filled with a gas core and protein shell. This allows the microbubbles to circulate through the cardiovascular system and return the ultrasound waves, creating a highly reflective image. There are multiple applications in which contrast - enhanced ultrasound can be useful. The most commonly used application is in the enhancement of LV endocardial borders for assessment of global and regional systolic function. Contrast may also be used to enhance visualization of wall thickening during stress echocardiography, for the assessment of LV thrombus, or for the assessment of other masses in the heart. Contrast echocardiography has also been used to assess blood perfusion throughout myocardium in the case of coronary artery disease.

TREADMILL TEST /CARDIAC STRESS TEST

A TMT or cardiac stress test (also referred to as a cardiac diagnostic test, cardiopulmonary exercise test, or abbreviated CPX test) is a cardiological test that measures the heart's ability to respond to external stress in a controlled clinical environment. The stress response is induced by exercise or by drug stimulation.

Cardiac stress tests compare the coronary circulation while the patient is at rest with the same patient's circulation during maximum physical exertion, showing any abnormal blood flow to the myocardium (heart muscle tissue). The results can be interpreted as a reflection on the general physical condition of the test patient. This test can be used to diagnose coronary artery disease (also known as ischemic heart disease) and assess patient prognosis after a myocardial infarction (heart attack).

The cardiac stress test is done with heart stimulation, either by exercise on a treadmill, pedalling a stationary exercise bicycle ergometer, or with intravenous pharmacological stimulation, with the patient connected to an electrocardiogram (ECG). People who cannot use their legs may exercise with a bicycle-like crank that they turn with their arms.

The level of mechanical stress is progressively increased by adjusting the difficulty (steepness of the slope) and speed. The test administrator or attending physician examines the symptoms and blood pressure response. With the use of ECG, the test is most commonly called a cardiac stress test but is known by other names, such as exercise testing, stress testing treadmills, exercise tolerance test, stress test or stress test ECG.

A stress test may also use an echocardiogram (ultrasonic imaging of the heart) or a nuclear stress test (in which a radioisotope is injected into the bloodstream).

HOLTER MONITOR:

In medicine, a Holter monitor (often simply Holter) is a type of ambulatory electrocardiography device, a portable device for cardiac monitoring (the monitoring of the electrical activity of the cardiovascular system) for at least 24 to 48 hours (often for two weeks at a time).

The Holter's most common use is for monitoring ECG heart activity (electrocardiography or ECG). Its extended recording period is sometimes useful for observing occasional cardiac arrhythmias which would be difficult to identify in a shorter period. For patients having more transient symptoms, a cardiac event monitor which can be worn for a month or more can be used.

When used in the study of the heart, much like standard electrocardiography, the Holter monitor records electrical signals from the heart via a series of electrodes attached to the chest. Electrodes are placed over bones to minimize artifacts from muscular activity. The number and position of electrodes varies by model, but most Holter monitors employ between three and eight. These electrodes are connected to a small piece of equipment that is attached to the patient's belt or hung around the neck, keeping a log of the heart's electrical activity throughout the recording period. A 12 lead Holter system is also available when precise ECG signal information is required to analyse the exact nature and origin of the rhythm signal.

COMPUTED TOMOGRAPHY (CT) ANGIOGRAPHY

Computed tomography angiography (also called CT angiography or CTA) is a computed tomography technique used to visualize arterial and venous vessels throughout the body. This ranges from arteries serving the brain to those bringing blood to the lungs, kidneys, arms and legs.

MEDICAL USES

CTA can be used to examine blood vessels in many key areas of the body, including the brain, kidneys, pelvis, and the lungs.

CT angiography: Coronary CT angiography (CTA) is the use of CT scan to assess the coronary arteries of the heart. The subject receives an intravenous injection of radiocontrast and then the heart is scanned using a high speed CT scanner, allowing radiologists to assess the extent of occlusion in the coronary arteries, usually in order to diagnose coronary artery disease. CTA has not replaced invasive catheter coronary angiography. The procedure is able to detect narrowing of blood vessels in time for corrective therapy to be done. This method displays the anatomical detail of blood vessels more precisely than magnetic resonance imaging (MRI) or ultrasound. Today, many patients can undergo CTA in place of a conventional catheter angiogram. CTA is a useful way of screening for arterial disease because it is safer and much less time-consuming than catheter angiography and is a cost-effective procedure. There is also less discomfort because contrast material is injected into an arm vein rather than into a large artery in the groin.

OTHER USES

CTA is commonly used for the following purposes:
  • CT pulmonary angiogram (CTPA) to examine the pulmonary arteries in the lungs, most commonly to diagnose pulmonary embolism, a serious but treatable condition.
  • Visualize blood flow in the renal arteries (those supplying the kidneys) in patients with high blood pressure and those suspected of having kidney disorders. Narrowing (stenosis) of a renal artery is a cause of high blood pressure (hypertension) in some patients and can be corrected. A special computerized method of viewing the images makes renal CT angiography a very accurate examination. Also done in prospective kidney donors.
  • Identify aneurysms in the aorta or in other major blood vessels. Aneurysms are diseased areas of a weakened blood vessel wall that bulges out—like a bulge in a tire. Aneurysms are life-threatening because they can rupture.
  • Identify dissection in the aorta or its major branches. Dissection means that the layers of the artery wall peel away from each other—like the layers of an onion. Dissection can cause pain and can be life-threatening.
  • Identify a small aneurysm or arteriovenous malformation inside the brain that can be life-threatening.
  • Detect atherosclerotic disease that has narrowed the arteries to the legs.
  • Exclude coronary artery disease, especially in low