Myocardial stunning or transient post-ischemic myocardial dysfunction is a state of mechanical cardiac dysfunction that can occur in a portion of

myocardium Cardiac muscle (also called heart muscle or myocardium) is one of three types of vertebrate muscle tissues, the others being skeletal muscle and smooth muscle. It is an involuntary, striated muscle that constitutes the main tissue of the wall o ...

without

necrosis Necrosis () is a form of cell injury which results in the premature death of cells in living tissue by autolysis. The term "necrosis" came about in the mid-19th century and is commonly attributed to German pathologist Rudolf Virchow, who i ...

after a brief interruption in

perfusion Perfusion is the passage of fluid through the circulatory system or lymphatic system to an organ (anatomy), organ or a tissue (biology), tissue, usually referring to the delivery of blood to a capillary bed in tissue. Perfusion may also refer t ...

, despite the timely restoration of normal

coronary blood flow Coronary circulation is the circulation of blood in the arteries and veins that supply the heart muscle (myocardium). Coronary arteries supply oxygenated blood to the heart muscle. Cardiac veins then drain away the blood after it has been deoxy ...

. In this situation, even after

ischemia Ischemia or ischaemia is a restriction in blood supply to any tissue, muscle group, or organ of the body, causing a shortage of oxygen that is needed for cellular metabolism (to keep tissue alive). Ischemia is generally caused by problems ...

has been relieved (by for instance

angioplasty Angioplasty, also known as balloon angioplasty and percutaneous transluminal angioplasty, is a minimally invasive procedure, minimally invasive endovascular surgery, endovascular Medical procedure, procedure used to widen narrowed or obstructe ...

coronary artery bypass surgery Coronary artery bypass surgery, also known as coronary artery bypass graft (CABG, pronounced "cabbage"), is a surgical procedure to treat coronary artery disease (CAD), the buildup of plaques in the arteries of the heart. It can relieve chest ...

) and myocardial blood flow (MBF) returns to normal, myocardial function is still depressed for a variable period of time, usually days to weeks. This reversible reduction of function of heart contraction after reperfusion is not accounted for by tissue damage or reduced blood flow, but rather, its thought to represent a perfusion-contraction "mismatch". Myocardial stunning was first described in laboratory canine experiments in the 1970s where LV wall abnormalities were observed following coronary artery occlusion and subsequent reperfusion.

Cause

Clinical situations associated with myocardial stunning include: * acute

myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when Ischemia, blood flow decreases or stops in one of the coronary arteries of the heart, causing infarction (tissue death) to the heart muscle. The most common symptom ...

(AMI) with early reperfusion *

unstable angina In dynamical systems instability means that some of the outputs or internal states increase with time, without bounds. Not all systems that are not stable are unstable; systems can also be marginally stable or exhibit limit cycle behavior ...

* after percutaneous transluminal coronary

(PTCA) * after cardiac surgery * 'neurogenic' stunned myocardium following an acute cerebrovascular event such as a

subarachnoid hemorrhage Subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space—the area between the arachnoid (brain), arachnoid membrane and the pia mater surrounding the human brain, brain. Symptoms may include a thunderclap headache, severe heada ...

* in patients undergoing chronic hemodialysis, chronic myocardial stunning may lead to heart failure Myocardial stunning has been implicated in the development of Takotsubo (Stress) cardiomyopathy.

Pathophysiology

The underlying mechanisms of myocardial stunning have remained the subject of debate for several decades. Two leading hypotheses implicate reperfusion-induced oxygen free-radical damage and altered calcium flux resulting in intracellular hypercalcemia and desensitization of myofilaments. After total ischemia occurs, the myocardium switches immediately from aerobic glycolysis to

anaerobic glycolysis Anaerobic glycolysis is the transformation of glucose to lactate when limited amounts of oxygen (O2) are available. This occurs in health as in exercising and in disease as in sepsis and hemorrhagic shock. providing energy for a period ranging fr ...

resulting in the reduced ability to produce high energy phosphates such as ATP and Creatinine Phosphate. At this point, the lack of the energy and lactate accumulation results in cessation of contraction within 60 seconds of

(i.e. Vessel Occlusion). Subsequent to this is a period of "myocardial stunning," in which reversible ischemic damage is taking place. At approximately 30 minutes after the onset of total ischemia the damage becomes irreversible, thereby ending the phase of myocardial stunning. The generation of oxygen-derived ree radicalsduring the initial period of reperfusion after ischemia is believed to contribute to the pathogenesis of myocardial stunning. Some evidence suggests that brief, repetitive episodes of myocardial ischemia may result in chronic myocardial stunning and ventricular contractile impairment.

Diagnosis

Imaging techniques such as

echocardiography Echocardiography, also known as cardiac ultrasound, is the use of ultrasound to examine the heart. It is a type of medical imaging, using standard ultrasound or Doppler ultrasound. The visual image formed using this technique is called an ec ...

, ventriculography, and

nuclear imaging Nuclear medicine (nuclear radiology, nucleology), is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging is, in a sense, ''radiology done inside out'', because it reco ...

can be used to detect a contractile dysfunction following reperfusion after an episode of ischemia. The area of dysfunction should also maintain normal perfusion, detected via

Positron Emission Tomography Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, r ...

, echocardiography with contrast, and/or thallium scintigraphy in order for a diagnosis of myocardial stunning to be considered. However, there are many practical challenges to diagnosing myocardial stunning using these methods. Accurate detection of regional myocardial blood flow and contraction function abnormalities must be detected at levels of high sensitivity. The diagnosis of myocardial stunning must also be differentiated from other conditions such as

hibernating myocardium In cardiology, hibernating myocardium is a state when some segments of the myocardium exhibit abnormalities of contractile function. These abnormalities can be visualised with echocardiography, cardiac magnetic resonance imaging (CMR), nuclear me ...

and persistent (silent) subendocardial ischemia, which can also co-exist with superimposed stunning.

Management

Treatment considerations for myocardial stunning should be determined based on the clinical judgment of the cardiologist or physician, the degree of LV impairment and symptoms, and the wishes of the person. Some evidence supports the use of inotropic drugs in the case of severe myocardial dysfunction. Results from canine experimental trials investigating the oxygen free-radical hypothesis for myocardial stunning have shown a reduction in free radical generation and improvement in myocardial function following anti-oxidant infusion.

References

External links