Cardiovascular tests

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Angiography is a test used to image blood vessels. With MRI it can be performed with or without the use of a c0ontrat agent. With CT a contrast agent is entered into an artery. During the procedure a series of X-rays are taken to create a map of the blood vessels. The conventional angiogram provides an accurate way to assess the integrity of arteries of the head, neck, chest, abdomen and extremities. CT and MRI angiography is used to evaluate the degree of narrowing or dilatation of blood vessels and to assess the quality of collateral blood flow to a region. The study may also reveal disruption of the arterial wall such as that seen with arterial dissection. The study is also used to detect aneurysms, as well as, arterial, venous and arterial-venous vascular malformations. A conventional contrast-based angiogram is an invasive procedure requiring the insertion of a catheter. There are risks associated with the use of contrast. A magnetic resonance angiogram (MRA) can be period with or without the use of a contrast agent. The use of contrast can sometime offer greater blood vessel detail than non-contrast studies. 

Body composition analysis refers to quantitative assessment of the distribution of muscle, fat, and water in the body. Body composition can be measured using a variety of different methods. One of the most accurate and practical methods is bioimpedance analysis (BIA). Body composition measurements play an important role in health, disease and sports. Excess body fat and abnormal distribution of body fat increases the risk for many diseases. Common disorders include metabolic syndrome and diabetes. In sports, excess fat or an abnormal ratio of fat to muscle impairs physical performance and places more stress on the spine and extremity joints. CNI uses state of art bio impedance technology to assess lean body mass, fat mass, water distribution, the body mass index (BMI), percent body fat (PBF), as well as, muscle and fat distribution. 

Doppler ultrasound uses reflected sound waves (sonar) to help evaluate the velocity and quality of blood flow through an artery or vein. The sonar is also used to evaluate structural relationships (anatomy) and structural integrity. During the procedure the patient reclines on a table. The technician or physician applies a hand held transducer over the blood vessels to be evaluated. The transducer emits sound waves, which are reflected from the vessel and moving blood flow.

          Specialized applications of doppler ultrasound include:

• Transcranial and Carotid Ultrasound: The lesion responsible for transient ischemic attacks (TIA), strokes and vertebrobasilar ischemia usually lies within the carotid or vertebral arterial system. Through the use of non-invasive sonography, it is possible to rapidly and reliably evaluate these vessels in their extracranial and intracranial course. The ultrasound study provides valuable information which can be used for effective therapeutic planning.
• Carotid and Vertebral Ultrasound (Extra-Cranial Cerebrovascular Duplex Scan): There are four large arteries which deliver blood flow to the brain. These vessels are the pair of carotid arteries and the pair of vertebral arteries. Carotid arterial assessment using non-invasive real time ultrasound imaging, combined with doppler color and spectral analysis is fast becoming the test of choice for screening and characterizing hemodynamic occlusive disease in the neck. Initial evaluation of the neck should include assessment of the right and left carotid as well as the vertebral arteries.

                         Carotid duplex scanning is a cost effective and accurate screening test and provides the             

                         attending physician(s) with valuable information about the degree of artery narrowing  

                         (stenosis) and the type of plaque which may be present in the artery. Vertebral artery circulation 

                         may also be assessed before or after exercise in order to assess whether there is a subclavian 

                         steal syndrome. An ultrasound study may be ordered if your physician hears an abnormal 

                         sound over an artery (bruit) or if he or she suspects arterial insufficiency to the brain. 

• Ankle Brachial Index (ABI): The ankle brachial index is a simple non-invasive screening test which uses doppler ultrasound to help detect reduced arterial blood flow to an extremity. The ankle/arm pressure index also known as the ankle/brachial index, abbreviated ABI is a test used to evaluate and compare the systolic blood pressure at the distal leg (ankle) to that of the arm (brachial). The ABI provides an objective measure which can be used to detect and to monitor the progression of occlusive blood vessel disease. It can also be used to evaluate the effectiveness of a treatment plan.

                         With progressive arterial narrowing there is a corresponding fall of the systolic blood pressure 

                         below the site or sites of artery obstruction or narrowing. The extent to which the systolic 

                         pressure falls is dependent upon the extent of blood vessel occlusion (narrowing) and the   

                         integrity of collateral (additional) blood flow though other less compromised vessels.

                         To perform the study a pneumatic blood pressure cuff is applied to the limb to be tested and a 

                         sensing unit (often a probe) is placed over a designated artery below the level of the cuff. The 

                         cuff is rapidly inflated above systolic pressures, subsequently obliterating the flow to the region 

                         be evaluated. As the pressure in the cuff is gradually deflated, the point at which flow is 

                         resumed is recorded as the opening or systolic pressure. 

                        The ABI findings are usually correlated with corresponding waveform analysis. A significant 

                        drop in arterial systolic pressure in one limb suggests reduced blood flow secondary to 

                        obstruction of one or more blood vessels. The presence of more subtle arterial obstructive   

                        disease can be detected by increasing blood flow and blood pressure, either by exercise testing 

                        or by inducing reactive hyperemia with an occlusive cuff. Patients with calcified vessels 

                         (arteriocalcinosis) such as that seen in diabetics may present with falsely elevated ankle             

                         pressures. In this case, pressure measurements can be made at the fingers or toes using 

                         photoplethysmography (PPG) for more accurate results.

• Toe or Finger Systolic Pressure Index: The prevalence of peripheral arterial disease is about 20-fold higher in patients with diabetes mellitus than in age-and sex-matched controls. It is therefore important to evaluate individuals with diabetes and suspected blood vessel disease for large and small blood vessel disease. Arterial disease in this population tends to be more severe and widespread than in the general population. Calcification of the peripheral arteries can render it difficult to obtain reproducible ankle systolic blood pressures. Because medial arterial wall calcification does not extend into the smaller diameter arteries of the fingers or toes it is possible to assess perfusion pressure by measuring finger or toe systolic pressures using phototplethysmography. In some cases the finger/brachial or toe/brachial index (TBI) may be a better indicator of reduced blood flow than the more traditional ankle/brachial index (ABI). The toe/finger systolic pressure can be expressed as a ratio of systolic pressure recorded from the toe (leg) and the finger (arm).

Cardiac ultrasonography (echocardiography) is a valuable non-invasive tool for imaging the heart and surrounding structures. It can be helpful for establishing a specific diagnosis and estimating the severity of various cardiac diseases. It is important to recognize, however, that the cardiac (heart) ultrasound exam is only a part of a more comprehensive heart work-up. Findings on the echocardiogram must be integrated with information obtained from the history and physical exam, cardiac and pulmonary auscultation, electrocardiogram (ECG), thoracic radiographs (X-rays) and other pertinent ancillary tests in order to accurately render a diagnosis and personalized care plan.

In general, echocardiography is used to evaluate heart chamber size, heart wall thickness, heart wall motion, heart valve configuration and motion, and the integrity of proximal great vessels. Doppler blood flow evaluation in the heart during an echocardiogram will help determine if congestive heart failure is present or whether heart valve insufficiency exists. The study is also used to assess thrombus development during the course of evaluating individuals with signs and symptoms of cerebrovascular disease and those who have had a stroke. Many echocardiographic findings are quantified making it is easy to compare values between studies.

Specialized forms of echocardiography include: 

• Stress Echocardiography: A stress echocardiogram is an ultrasound test used to evaluate the valves and other structure of the heart, before and after exercise. 
• Transesophageal Echocardiogram: A transesophageal echocardiogram is a test used to see evaluate the function and structure of the heart. Placement of the ultrasound transducer in the esophagus improves the quality of images acquired. Subsequently, the test may reveal smaller region of developmental (congenital) or acquired abnormalities.
• Transthoracic Echocardiogram: A transthoracic echocardiogram is a test used to see evaluate the function and structure of the heart. The ultrasound transducer is placed over different areas of the chest to acquire imagines. This represents the safest and most common form of echocardiography.

Electrocardiography (ECG), often-abbreviated EKG, is a non-invasive test used for detecting and monitoring heart disease. The multi-channel 12-15 lead ECG is particularly helpful at locating regions of tissue compromise and subsequent electrical abnormalities within the heart. Electrical signals generated inside of the heart triggers the upper muscular chambers (atria) to contract thus moving blood into the lower chambers (ventricles). Electrical signals progress in a specific way to trigger the lower chambers (ventricles) of the heart to contract; thus, propelling blood through the lungs and the body. There are specialized groups of cells within the heart that create the electrical signals. The signals travel over special pathways of cells referred to as the bundle branches. The pattern of electrical signal transmission is influenced by the health of heart tissue, the amount of blood and oxygen delivered to the tissue and by the autonomic nervous system regulation. 

The electrocardiogram (ECG) is a test, which acquires an electrical recording of the heart from numerous angles. It is primarily used for the investigation of heart disease, although, it can be used to assess autonomic nervous system influence and regulation of the heart rate, rhythm and function. The resting ECG is performed by having the patient lie on a table on their back. A total of 12 to 15 superficial (stick on) recording electrodes are placed across the chest and on each of the extremities. The recording electrodes are hooked up to an interpretive computer, which provides a detailed printout of the results.

There are many different types of ECG tests which include the 12 lead resting ECG, the ambulatory ECG (Holter), the event recorder and the graded exercise test (GXT) or stress test. The ambulatory ECG refers to recording of the hearts electrical activity for a prolonged period of time such as 24 hours or more. During an ambulatory ECG the patient wears the recording unit on their waist with electrodes hooked to their chest as they go through their normal day. The patient may be asked to keep a time stamped diary while wearing the unit. 

Because the routine resting ECG is conducted over a very short period of time (10-15 seconds), the study may not reveal intermittent heart rate, heart rhythm or other forms of electrical irregularities which do not occur during the test period. There are specialized types of ECG protocols which can be applied during the course of a resting study to expand the examination process. The more common electrocardiographic studies are listed below. 

Specialized form of ECG studies include:

• Signal-averaged ECG: This study may be used to help identify risk factors associated with ventricular tachycardia or fibrillation (fast abnormal rhythm). The study is very similar to a routine resting ECG; although, with the exception that it takes approximately 20-40 minutes to complete. A sophisticated computer system is used to identify and magnify weak electrical signals in the heart that may otherwise be missed with a more routine study. The electrical patterns associated with multiple heartbeats are computer-averaged and enlarged to help the attending healthcare provider evaluate subtle patterns of abnormal electrical signaling which may reflect disease. 
• Exercise ECG (stress test): The exercise ECG study may be used to evaluate whether enough blood flow and oxygen reaches the heart during exercise. The term ischemic refers to a lack of oxygen and nutrient delivery to the heart, as well as, other tissues. The exercise ECG is typically done on a treadmill or a stationary bike to determine if ischemia is presentment during exertion. Electrodes are attached to the skin and linked to a compute to record and analyze electrical data acquired before, during and after exercise. By evaluating the heart while it is working harder, your doctor can better evaluate the limitation of the heart’s functions and determine whether blood flow to the heart is adequate during a period of increased demand. 
• Ambulatory ECG: This study is used to monitor your heart for rhythm abnormalities and ischemia (lack of oxygen) during normal activity for a prolonged period of time. A continuous study is usually performed for 24-48 hours. The study requires the placement of superficial electrodes onto the skin over the chest which is connected to a portable recording device, which is about the size of a portable (cellular) phone. The recording device can be attached to a belt or can be hung from a shoulder strap. Some recording devices have an event button, which you will be asked to push when you experience symptoms. Pushing the button marks the time of the symptomatic event onto the ECG recording so findings can be correlated with diary entries.
• Transmitted ECG: This study uses a recording device, which allows for transmission of ECG results through a telephone line or wireless system. This is helpful when symptoms are infrequent requiring a long recording time period. If an individual experiences possible heart-related signs or symptoms ECG data can be transmitted to a physician or to a service which in turn forwards the information to a physician for interpretation and reporting.
• Event Recorder: An event recorder may be used if heart symptoms are infrequent. An event recorder can be worn for a period up to 30 days. When experiencing symptoms, a button on the recorder is pushed which cues the unit to store ECG data before the event, during the event and for a period after the event. The acquired information can then be transmitted to an interpretive system or provider.

Pulse oximetry is a simple non-invasive method of monitoring the percentage of hemoglobin (Hb) in the red blood cell, which is saturated with oxygen. The pulse oximeter consists of a probe or special clip, which can be placed onto a patients’ fingertip, toe or ear lobe. Most pulse oximeters have an LED readout, which may be linked to a computer. The unit displays the percentage of hemoglobin saturated with oxygen. The normal value is 66-100%. Audible alarms can be set during a procedure or for general monitoring purposes. Oxygen saturation measurements can be compared between the digits of the upper extremities and the lower extremities by placing the unit on a finger and then on a toe. This approach may help reveal regional variations in blood flow.

T-wave Alternans (TWA) represents a specialized form of EKG used to detect the risk for developing irregular heart rhythms. The test requires placement of superficial specialized electrodes on the chest. The individual’s heart rate is typically raised to a submaximal level during which time electrical measurements are acquired and analyzed. T-wave alternans measures beat-to-beat fluctuations in the timing or shape of the ECG T-wave. The T-wave represents one element of the electrical wave complex associated with each individual heartbeat. TWA testing may be performed as part of a more comprehensive heart workup.

The tilt table study is often used to evaluate patients who have had syncope (loss of consciousness) or near-syncope (near loss of consciousness). It is an extremely simple study, and in most cases quite safe. A tilt table study is performed with the patient strapped to a table, which is then mechanically tilted to a predetermined upright position. 

The table is tilted while monitoring an individual’s pulse, blood pressure, electrocardiogram, and sometimes blood oxygen saturation. The patient may be left in a “motionless standing position” for 20 to 30 minutes. When the patient's syncope is reproduced during the test, a "positive" tilt table study is said to have occurred. 

During an upright tilt and while standing a person's cardiovascular system has to adapt to main adequate vascular perfusion and to prevent a significant portion of blood volume from pooling in the legs. These adjustments consist of a mild increase in heart rate, and a constriction of the blood vessels in the legs. When a normal individual is placed in an upright tilt, these cardiovascular adaptations occur very quickly, and there is no significant drop in the blood pressure. In patients with neurological conditions such as orthostatic hypotension and vasovagal syncope, the autonomic nervous system regulation of the cardiovascular response does not work right.