Detection Of Ischemic Heart Disease Biology Essay

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According to the world health organization cardiac related disease is one of the ruling causes of death over the past decade. According to Reimer (2010) ischemic heart disease IHD is the main cause of high morbidity /mortality cases in most industrial countries. IHD is a type of pathology that occurs when the blood supply to the heart muscle is impaired. This disease occurs due to a number of factors that influence its progress and severity; atheroma and thrombosis, are two of such factors but most importantly coronary artery disease CAD which is the most common of the later and the killer of one in every three patient of the nation population (39 %) Gray 2008. Other underlying reasons that could influences IHD include; smoking, diabetes mellitus and different life style choices like; diet or lack of exercise. This disease manifests as different cardiac mayopathies such as angina pectoris, acute coronary insufficiency and most commonly myocardial infarction (MI). Infarction of the myocardium happens in 35% of men ages 35-50; however, the rate for men declines when ages are above 55 and contrary increases for woman, it is one of the leading causes of death in developing countries and the United States.

According to (--) common causes of ischemic disease are full-thickness myocardial infarction, partial thickness infarction, myocardial stunning, and myocardial hibernation. Having all of such causes or one in the same patient could enormously cause a sever influence on the outcome result of the diagnosis; thus Fortunately, in the last two decades experience has increased with the use of imaging techniques that can detect and assess myocardial viability, metabolism, perfusion, and function. Accuracy of such diagnostic tools has increased substantially, each with its own strengths, weaknesses and availability in most health centres.

Detection (cardiac magnetic resonance CMR)

To detect disease before it reaches sever irreversible extents in the myocardium there are a number of imaging procedures used to diagnose the problem. Cardiac magnetic resonance imaging (MRI) is one of the most new and modernise tools employed in cardiac pathology diagnosis. During a CMR scan the involuntary action of the heart is not evident, and the motion is portrayed dominated by the images taken though out the scan. This dominance allows for a wide range of clinical applications such as the evaluation of congenital heart disease, cardiac masses, the pericardium, right ventricular dysplasia, and hibernating myocardium. CMR is done through the use of a series of advanced hardware and software that are specifically used to view the heart, this makes it less popular in respect to other low maintenance competing modalities such as; single-photon emission computed tomography (SPECT) and echocardiography which are more commonly employed in clinical practice.

Never the less, recent studies have indicated that MRI after the administration of contrast material can be used to distinguish between reversible and irreversible myocardial ischemic injury which has important clinical implications on patient prognosis. Having a better understanding of the patient the condition would direct the specialists towards revascularizations, which only benefits patients with a sufficient amount of viable myocardium and are unlikely to benefit those with, sever transmurally infarcted myocardium (---------).


The main concept of this paper is to provide a critical over view of the way cardiac imaging can be done by means of Magnetic resonance scanning. And, specifically indicate whether if MRI after the administration of Gadolinium (the Delayed Enhancement {DE-MRI} technique) can be used to differentiate between revisable or irreversible myocardial ischemic changes. Finally, the effect early detection will take on the patient's life (prognosis) and whether CMR scan coasts overcome the overall results.


Heart Anatomy

The heart is one of the largest involuntary muscles in the human body, constantly pumping and receiving blood throughout the whole body. Its shape changes according to each individual which makes scanning different for each patient. The location of the apex changes with the patient body shape, weight and whether the patient is standing or lying down.

In general, the heart is hollowed, muscular and con-shaped located between the lungs with its apex directed down and forward slightly to the left. Cardiac muscle is what makes up most of the heart and it is called (myocardium). The myocardium is lined and surrounded by two type of membranes the endocardium and pericardium. The heart is divided by the septum into right and left parts, each are further divided into an (upper) atrium as well as a (lower) ventricle (Figure 1). The heart has three located valves that control blood flow and they are; the semilunar, tricuspid, and bicuspid.

When the heart contracts it pumps blood to the lungs via the pulmonary artery from the right ventricle passing from the right atrium delivered via the vena cava. On the other hand, newly oxygenated blood returns to the left atrium via the pulmonary vessels passing through the left ventricle and eventually passing through the aorta. This contraction makes up continues motion that causes the further on explained artefact problems that faces a Cardiac scan.

Ischemic pathology,

Tissue when contaminated with ischemic changes and becomes damages it falls into one of three categories; stunned, hibernating and necrotic. On the other hand, According to (---) the term "viable" describes myocardial cells that are alive and hence also the myocardium that they constitute.

2.2.1. Stunned myocardium

Stunning is a form of contractile dysfunction of viable myocardium caused by a brief period of ischemia followed by restoration of perfusion (----). It may be the result of reperfusion injury whereby restoration of normal blood flow leads to generation of free radicals and a transitory overload of calcium within the myocytes and temporary damage to the contractile mechanism, indicated by (---).

2.2.2. Hibernating myocardium

Hibernation is also a state of contractile dysfunction in viable myocardium, but now in the setting of chronic ischemic heart disease. In contrast to stunned myocardium, in which function recovers spontaneously, hibernating myocardium requires an intervention such as revascularisation for recovery (----). Hibernating myocardium is therefore normally defined as viable but dysfunctional myocardium that improves in function after revascularisation, but it is possible that medical therapy might also be effective in relieving hibernation by abolishing ischemia (----). The definition, of course, assumes that revascularisation is successful and that the procedure itself does not lead to damage of the relevant area of myocardium (---). It is important to distinguish between retrospective and prospective definitions of hibernation. Myocardium cannot strictly be defined as hibernating until improvement of contraction after intervention has been demonstrated. However, identification of hibernation is needed preoperatively for patient management and so a number of prospective definitions are used in the imaging literature.

2.2.3. Necrotic myocardium,

According to rung (2009) necrotic tissue (none viable) myocardium it is a stage that when tissue reaches it is no longer contains living cells (myocytes); there for it is unable to be returned to normal function.

2.2.4. Contrast agent (gadolinium) effects on myocardium,

In reference to Klem 2006 effected tissue accumulates gadolinium and thus visualised of hyper signal intensity after 10 min on the least of injections. This happens due to the fact that regular cell constitute of intra cellar space (75% water) thus when extracellular contrast agent is produced a rapid wash out occurs. Conversely, necrotic nonviable tissue retains contrast when it reaches the cell and remains in longer and the higher signal enhancement is produced.

Imaging technique,

High resolution scans is one of the advantages of using CMRI as diagnostic of effected myocardium. However, the heart as a constantly moving organ presents the scanning procedure with a major difficulty. Cardiac motion and respiratory motion due to the heart location are two of the key obstacles that affect image representation. Motion on MR Images produce an artefacts which reduce image resolution and produce the image with blurring and either produce obstacles which prevent visualisation of the desired pathology, or artefact that mirrors none existing pathology and created an none existing condition with in the image. In the cause of ischemic changes the artefact blurred produces enhancement delineating other myopathilies within the myocardium degrading the diagnosis of the patient and resultant outcome of the patient condition. Many techniques are undertaken to control such motion and prevent artefacts from obscuring pathological changes.

Cardiac motion,

Gating and triggering are two of the tools that are commonly used in cardiac scans to present a high resolution image. Triggering techniques being least of the two frequently used This is because triggering usually takes longer due to the fact it has to measure a full cardiac cycle to trigger, also, if any reduction to the cycle capture is done some scan information gained by end diastole will be lost. On the other hand, gating which is considered to be the golden standard is faster way to prevent motion artefact. It continuously acquires data thus the information by end diastole lost on triggering is preserved in gating. (Figure 2) ECG gating can be performed prospectively or retrospectively.

Common problems with ECG-triggered acquisitions include poor or inaccurate R wave detection (e.g. triggering off a prominent T wave) and patient arrhythmias. R wave-detection problems can often be resolved by adjusting electrode position or toggling the lead polarity. Arrhythmias can result in inaccuracies in evaluation of cardiac function. Acquisition time can also be increased, as some heartbeats may not trigger data acquisition. The effect of arrhythmias can be mitigated with very fast sequences (e.g. single-shot fast spin echo) or real-time sequences.

Conversely, according to (sprung) using pulse triggering could be a third way of cardiac motion elimination (synchronization); nevertheless, it is not as reliable as ECG due to pulse wave delays and wider signal peaks.

Breathing motion,

To overcome respiratory motion examinations are done while patients are on breath hold (BH). To allow for such technique scan time must be short enough to be within the patient capability to avoid artefact motion. This is done by using scanning sequences that would allow for short breath holds like; Gradient echo sequences or the introduction of sense and parallel imaging.

Some scanners would include a respiratory triggering tube. Placed on the patient's trunk, the tube will trigger diaphragm motion and thus trigger image capture according to patient regular breathing. This technique is not commonly used as they are scanner specific and have to be separately ordered.

CMR Imaging physics,

As mentioned previously the main idea in CMR imaging is reduction of time or fast scanning. Using different aspects of k-space data sampling is a way to accomplish that. It is a technique to provide the desired resolution without compensating scanning time or data collection. There are different ways to fill k-space but the golden standard for CMR is segmentation.


Segmentation refers to the strategy of segmenting data acquisition over multiple cardiac cycles. The degree of segmentation can range from one k - space line per cycle (non - segmented), up to acquisition of all of the lines needed to reconstruct an image (single - shot). Any level of segmentation can be used with each of the basic methods of echo formation (gradient echo, spin echo, SSFP, EPI).Overall acquisition time is inversely related to the number of lines acquired per image each cardiac cycle (lines per segment), that is, the more lines per segment, the shorter the scan time. The trade - off is in temporal resolution; the more lines per segment, the poorer the temporal resolution. Modern CMR sequences for cine, flow, and delayed - enhancements are designed to acquire enough lines per segment to reduce the scan time to a reasonable breath -hold. The success of segmented imaging depends not only on patient breath - hold, but also on a regular cardiac rhythm to ensure that the k - space data from each cardiac cycle is capturing the heart in the same respiratory and cardiac positions. In patients with severe arrhythmia or an inability to breath - hold, real - time or single - shot methods are commonly used due to their insensitivity to respiratory motion effects.

Types of cardiac MR sequences,

As mentioned previously cardiac sequences need to be specific as they are restricted to both cardiac cycles and breathing motion. In general a spine echo (SE) and a gradient echo (GRE) are most frequently used for cardiac imaging and they vary in dominance according to the pathology being imaged.

Spine echo (SE):

Spine echo sequences in cardiac MRI are called black (Dark) blood sequences. "Black blood" MR images are produced with sequences designed to null the signal of flowing blood. These images allow for anatomic assessment of the heart and vascular structures without interference from a bright blood signal. While black blood sequences are standard in most imaging protocols, they are particularly important for assessment of cardiac masses, the myocardium (e.g. in suspected arrhythmogenic right ventricular dysplasia), and the pericardium. SE sequences as a rule are acquired through an application of a 90 and 180 degree Radio frequency (RF) pulse. Normal Blood being motor and in constant motion when passing through an RF excitation pulse does not receiving both RF waves and thus remains not fully excited showing up as dark (black) in MR images while motionless static surrounding tissue which receives both appears of high signal intensity. In clinical practice, there are three general options for black blood imaging and they are; Half-Fourier single-shot fast spin echo with double inversion recovery, Breath-hold single-slice fast spin echo with double inversion recovery or Multislice fast spin echo.

Gradient echo (GRE):

On the other hand, gradient echo sequences are called Bright Blood sequences due to the wash out effect of fresh blood within each image acquisition. In a Bright Blood images he surrounding tissue gets consecutive amounts of signal which gets saturated however, blood being motor receives signal but leaves the slice and freshly new blood replaces it with no signal thus producing the bright blood effect. GRE sequences are important when it comes to imaging of the heart because of their short repetition times thus resulting in lesser scanning times. This is vital for cardiac motion and respiratory motion artefact reduction.

SE and GRE are the most basic sequences that are used for cardiac imaging, however, hybrid sequences which are combination of both is another way that can also assists in cardiac imaging. The type of imaging sequence that is used for DE-CMRI is a 2D Inversion recovery Turbo FLASH pulse sequence.

Magnetisation preparation in CMR,

Contrast enhanced agents are a big part of the delayed enhancement study for IHD detection. It is based on T1 weighted ultrafast gradient echo or steady state gradient echo sequences. The advantage of 3D acquisitions is their capacity to explore a large volume with a single breath-hold, whereas 2D acquisitions offer better spatial resolution (less blurring due to motion), and provide better visualization of transmural enhancement extension (---). As the contrast of these sequences is optimized; the enhanced signal has to be suppressed to increase contrast resolution of the affect tissue. Methods to contain such signal include; inversion recovery, which best used for delayed enhancement pathology or PSIR technique (Phase Sensitive Inversion Recovery). Also, saturation recovery, But it is best used for dynamic (perfusion) contrast enhancement studies.

Inversion Recovery

The technique uses a specific TI to null the healthy myocardial signal form the contrast enhanced image. The TI is determined beforehand in a dedicated sequence (TI scout) to test a range of TI so the user can choose the TI with the best suppression of the healthy myocardial signal (~ 300 msec).

PSIR technique (Phase Sensitive Inversion Recovery),

It is more robust and is independent of TI. This technique incorporates acquisition of reference slices in an ultrafast IR-GE sequence, without lengthening sequence time. These reference slices serve to correct the phase polarity of the slices at TI, restoring T1 contrast, as opposed to a simple magnitude analysis of the signal. Using single shot PSIR sequences in delayed enhancement MRI can be useful in the case of patient that finds breath holding is difficult or have irregular heartbeats to avoid any motion artefacts.


3.1. Case study,

Patient presented with history of myocardial infarction (MI) and left ventricle dysfunction. The request was to assess viability of the myocardium and heart tissue.

A duplex ultrasound scan was done three days prior to the referral for the carotids and showed episodes of irregular heart rate during examination.

Also, an echocardiogram was performed to assess the LV systolic function and was indicated by the same history of (MI) and stroke. The ECG showed ischemic cardiomayopathy with depressed LV systolic function and mild to moderate mitral regurgitation.

Patient preparation,

To ensure that the area of the ECG placement is clean of any artefact the patent before commencing the scan needs to be prepared. Steps would include detection of chest hair if so Removal is necessary, clean and roughen skin surface, remove oil and perspiration to allow better contact of electrodes care should be taken to clean with abrasive prep pad or Nuprep gel, not alcohol and above all dry area completely.

Hardware and software,

A 1.5-T scanner (Siemens Avanto) was used for the examination. But in general the minimum requirement for cardiac imaging should include a substantially high magnetic field of at least 1.5T and robust gradien coils of 15 MT/m and slew rates of at least 100 T/ms; these demands are due to the rapid motion of the heart and blood movement which places a considerable amount of stain on the system itself. Using high magnetic fields would allow for higher signal to noise ratio (SNR) and faster imaging to reduce motion with breath holds without compromise to image temporal resolution.

Positioning and scanning,

Patient is then is asked to lay supine on the table and ECG gates were placed on the chest in an L shape formation to get the proper cardiac gate. A 10 second duration time should be given for the ECG to get their learning point for proper peak wave's adjustment. The phase- array coil was placed on the patient chest to cover the area to be imaged. A call bell for anxiety and headphones for the instructions were both given to the patient prior to Iso- cantering.

The MRI procedure included two segments; before and after injection of contrast agents.


Study of the left ventricle (LV) using an ECG-triggered breath hold segmented steady-state free precession (SSFP; true fast imaging with steady-state free precession [FISP]) Cine sequence (TR/TE, 3.0/1.5 msec; flip angle, 60°) with a slice thickness of 8 mm. After three standard long-axis slices were obtained, contiguous short-axis slices were acquired to cover the entire LV without an inter slice gap (table).


An injection of 0.2 mmol/kg body weight of Multihance, LE scans were collected in three long-axis and all short-axis orientations by using a breath-hold ECG triggered 2D inversion recovery turbo FLASH sequence (TR/TE, 1156/3.2 msec; flip angle, 25°) table. In Images were acquired subsequently up to 8-10 min after injection. The inversion time (TI, non-selective inversion pulse) was adjusted manually between 270 and 300 msec to null the signal of normal myocardium.




Correction if needed



Insure a single breath hold and since there is 8.8 echo it compensates for the information needed


Distance factor


FOV read


FOV phase


Slice thickness








Flip angle


Base resolution


Phase resolution



130 Hz/Px






13 sec

TI scout,

Determine optimal TI for nulling of normal myocardium, prescribe as a mid ventricular short axis slice, rotate FOV to avoid wrap, single breath hold, trigger on every second heartbeat, capture cycle for optimal acquisition window.

Short Axis Delayed

prescribe 10 slices, phase sensitive inversion recovery Turbo FLASH technique, provides both magnitude and real images, adjust TI for nulling of normal myocardium, rotate FOV to avoid wrap, multiple breath holds, trigger on every second heartbeat, capture cycle for diastolic gating.

Four-Chamber Delayed

prescribe 1 slice, phase sensitive inversion recovery Turbo FLASH technique, provides both magnitude and real images, adjust TI for nulling of normal myocardium, rotate FOV to avoid wrap, single breath hold, trigger on every second heartbeat, capture cycle for diastolic gating.

Two-Chamber Delayed

prescribe 1 slice, phase sensitive inversion recovery Turbo FLASH technique, provides both magnitude and real images, adjust TI for nulling of normal myocardium, rotate FOV to avoid wrap, single breath hold, trigger on every second heartbeat, capture cycle for diastolic gating.



Overall Morphology and function,

The left ventricle is mildly dilated with an EDD of 61 mm with mild LVH with the septum measuring 13 mm and the posterior wall measuring 11 mm. There is thinning and sever hypo-kinesis of the mid and distal anterior wall, distal septal wall and the entire apex is aneurismal. No apical thrombus is appreciated. LV systolic function is impaired with estimated EF in the 30-35% range. There is at mid mitral regurgitation and the left atrium is mildly dilated at 49mm. The right ventricle appears top normal in size with normal systolic function. The right atrium appears mildly dilated.

Delayed enhancement imaging,

Images show an extensive area of mostly transmural infarct in the mid and distal anterior walls and entire apex. The other segments appear viable.

Summary of findings,

Ischemic cardiomayopathy was discovered with a dilated LV and depressed systolic heart function. Also, evidence of old transmural anteroapical infarct was present in this study.



MRI as an imaging modality

In patients with ischemic cardiomyopathy, DE-CMRI is used routinely to accurately detect and size infarcted myocardium. It is arguably the gold standard viability study and accurately predicts hibernating myocardium and response to revascularization


Advantages vs. Disadvantages

CMRI vs. Other procedures

Currently, there are limited prognostic data in patients with myocardial viability as assessed by cardiac MRI. However, there is a wealth of literature on the use of scintigraphic techniques (PET, single-photon emission computed tomography [SPECT]) and DSE for identifying high-risk patients whose survival could be prolonged by revascularization. In general, SPECT perfusion studies and DE-MRI have greater sensitivity but lower specificity for identifying viable myocardium compared with techniques. Data on prognosis based on MRI assessment of viability have only just begun to emerge. Nonetheless, DE-MRI has shown excellent accuracy in the delineation of scar when compared with scintigraphic techniques. (Klein et al) 62 studied 31 patients with ischemic cardiomyopathy and found a close correlation between the extent of myocardial scar identified by DE-MRI and PET. Though quantitative assessment of infarct mass by DE-MRI correlated well with PET infarct size (r_0.81, P_0.0001), DE-MRI identified subendocardial scar more frequently than PET. These authors also compared wall thickness (end diastolic and end systolic) and wall thickening at rest in combination with DE-MRI for viability, using PET as the gold standard, and found significantly better results for DE-MRI. These findings are concordant with those of (Wagner et al) 63 who recently compared DE-MRI with SPECT in 91 patients. In this convincing study, both imaging modalities were also evaluated against histological confirmed infarctions that were either transmural or subendocardial (_75% transmural or _50% transmural extent of the left ventricular wall segment, respectively). Histological confirmed subendocardial infarcts were detected by DE-MRI in 92%, whereas SPECT detected only 28%. Moreover, in the patient series, almost half of the subendocardial infarcts were missed by SPECT as compared with DE-MRI. The clinical reproducibility of infarct size by DE-MRI has been evaluated and compared with the reproducibility of SPECT imaging by Mahrholdt et al.12 In this study, the size of chronic infarcts (which were between 4% and 27% of total left ventricular mass as measured by DE-MRI) showed no significant change in size between 10 and 30 minutes after contrast administration and compared favourably with quantification by SPECT.

Costs and economical worth

CMR has the potential to provide myocardial perfusion measures. Evidence in small patient samples reveals a sensitivity and specificity of 87% and 85%, respectively, versus catheterization as the gold standard, and improved detection of infarction versus SPECT. Considerable amounts of diagnostic and prognostic data are available with SPECT however and despite a substantial radiation burden of SPECT, it appears that perfusion CMR may take time to become competitive due to the current favourable reimbursement for perfusion SPECT, with function as an add-on. The detection of subendocardial ischemia by CMR techniques could prove to be clinically and cost effective for large segments of the SPECT population (for example women evaluated for chest pain symptoms). Despite this initial caution on the use of perfusion, viability testing with CMR may become the gold standard for the assessment of patients with LV dysfunction presenting for evaluation and consideration of coronary revascularization. Using a model of high risk cost-effectiveness, evidence of CMR viability would result in improved patient outcome with coronary revascularization and reduced cost (due to reduced hospitalisations for heart failure, acute myocardial infarction, etc.).


Cardiovascular MRI provides a unique tool to assess multiple interrelated clinical markers of viability in a single test. Its overall accuracy appears to be equivalent, and in several reports, superior to the currently available techniques, including PET imaging. Considering the greater spatial resolution compared with PET and the wealth of correlative pathological data, DE-MRI may well represent the new gold standard in the detection of irreversibly damaged myocardium. However, the clinical data to date consist of relatively small numbers of patients, and setting a convincing new standard will require larger and more definitive clinical trials. Nonetheless, it is apparent that the full potential of CMR has only just begun to emerge, and its impact on the management of ischemic left ventricular dysfunction will continue to increase.