Introduction:
Advancements in diagnostic interventions are a boon for the medical field, as it aids in the prompt understanding of the various factors which are otherwise inaccessible and unknown. The extension of the application of the magnetic resonance imaging technique gave rise to a new horizon and rays of hope for heart patients with known cardiac insults or injuries. Cardiac magnetic resonance imaging (MRI) aids doctors not only in the detection of various heart disorders but also provides insights into the scope of recovery and repair of certain cardiac ailments.
What Is MRI?
MRI is quite a familiar and widely employed form of diagnostic procedure, which works with the help of a magnetic field to picture the various vital organs in the body. The absence of hazardous radiation and exploratory procedures makes it unique and acceptable. Water comprises a major proportion of the human body. These water molecules house atomic units called protons. In magnetic resonance imaging, these protons are targeted by exposing the person to a specific magnetic field.
Upon exposure, the proton molecules get influenced by these magnetic waves, and consequently, these proton molecules line up and orient in a specific direction. As soon as the exposure of the magnetic waves is turned down, the proton resettles in its usual position, and this process is coupled with the liberation of energy. This directional shift in the proton orientation and the energy changes aid in picturing the internal structures.
What Is Cardiac MRI?
When the MRI technique is employed to visualize the heart and associated structures, it is medically called cardiac magnetic resonance imaging. It provides a high-resolution, three-dimensional picturization of the cardiac area. Cardiac MRI is employed to detect various cardiac abnormalities that fail to reflect changes in other diagnostic interventions. It is widely advised for conditions like:
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Aortic diseases (impairment in the aortic blood vessel).
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Cardiomyopathy (conditions involving the heart muscles).
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Pericardial disease (diseases that impact the outer heart covering)).
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Congenital heart disease (inborn discrepancies in the heart).
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Valvular heart diseases (impaired heart valves).
In addition to the disease diagnosis, cardiac magnetic resonance imaging is employed to analyze the progression of certain cardiac conditions and determine the prognosis of certain treatment modalities. It aids in selecting treatment choices for the condition by explaining the range and nature of the damage to the heart muscles.
What Is Myocardial Viability?
Myocardial viability is a specific term that signifies the viability or practicability in bringing back the insulted heart muscles into their functional and healthy form. Following a cardiac event like myocardial infarction (hindered circulatory flow to the cardiac musculature), the heart muscle cells have undergone remarkable insult and impairment. Cell impairment can be either restorable or permanent. Viability testing provides a conclusive answer about the nature of the impairment. The compromised blood flow might have precipitated a certain degree of damage, but if the damage happened is within the viability range. Accordingly, the treatment can be modified to focus on the recovery of those insulted but viable cells. Reperfusion (reinstating the blood flow) helps enhance the heart's overall functional status and elicits a remarkable hike in the cardiac lifespan.
What Is the Role of Cardiac MRI in Assessing Myocardial Viability?
Cardiac magnetic resonance imaging modality is an effective and promising tool for gauging the viability of the heart muscles that have undergone an insult. The cardiac muscles are crucial for maintaining the rhythm and function of the heart. An appreciable collapse or termination of the blood flow to those muscular units can precipitate myocardial infarction.
A few muscle cells might be irrecoverably damaged following an infarction due to oxygen deprivation. However, very few cells might remain in a partially impaired hibernating stage, which can be brought back to action upon re-establishing the hindered blood flow. These hibernating muscle cells are not restricted to myocardial infarction but are also reported following various cardiovascular events.
The viability of the cardiac muscles cannot be promptly detected by triggering with external stimuli as there are minimal chances for the muscle cells to elicit response and contraction following an ischemic (oxygen deficit) insult. So cardiac magnetic resonance imaging is also advised for various ischemic heart conditions. A cardiac MRI gives a clear picture of the scope for restoring the functionality of the damaged cell. It also aids in identifying the restorable damage in the cardiac musculature that has occurred before a blatant cardiac insult. Blood flow enhancement procedures (reperfusion) can be undertaken to evoke the silenced and severed cardiac muscle cells, which hinders the advancement of the infarction by restoring the viability and longevity of those cells.
Furthermore, cardiac MRI provides insights into the range of obstructions or hindrances to the circulation and possible contractile power remaining with the severed muscle cells.
What Are the Different Cardiac MRI Techniques Employed for the Assessment of Myocardial Viability?
Diverse technical approaches are being discussed for the gauging of myocardial viability. Two distinct approaches that are widely employed for detecting the viability status of the myocardium include the following:
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Contractile Reserve Assessment: In this technique, the heart muscle's contractility (ability to elicit contractions) is considered. The heart muscle contractility is determined by two physiological states - stress and rest. The difference between the two gives the contractile reserve capacity. Dobutamine medicine is given to evoke stress, and then the contractility is assessed with the help of a cardiac MRI.
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Late Gadolinium Enhancement (LGE) Imaging: It is popularly known by the synonym delayed contrast enhancement and is identified as the hallmark interventional approach for analyzing the viability status of the heart muscles. This technique introduces a gadolinium-based contrast agent (GBCA) into the patient's vein as an injection before being exposed to MRI. Live and viable myocardium does not permit the entry of these metal contrast agents inside the muscle cell. Therefore GBCA gathers and piles up within the spaces between the myocardial cells. Thus LGE measures the viability by checking the integrity of heart muscle cells.
Conclusion:
Cardiac magnetic resonance imaging, popularly known as CMR, is a guaranteed intervention tool that can give a clear and accurate idea about myocardial viability. It helps tackle an advancing ischemic condition and prompt recovery following myocardial events. The treatment strategies can be designed taking into account the viability status. Timely intervention to reinstate the perfusion (blood flow) helps check the development of irreversible ischemic impairments in the muscle cells. It is endorsed as the standard testing modality for myocardial viability.
