The diminished left ventricular filling volume obstructs cardiac output, resulting in diminished blood flow to intramural coronary vessels and the rest of the body. This leads to diminished left ventricular filling volume and contractility secondary to the stiffened, overgrown myocardium. Hypertrophic cardiomyopathy is a myocardium disease in which a portion of the left ventricle asymmetrically hypertrophies, often in the septum. Hypertrophic cardiomyopathy and arrhythmogenic right ventricular cardiomyopathy are two sources of cardiac syncope that are recognizable by specific histopathologic findings. Pulmonary hypertension and pulmonary emboli will lead to a blockade of flow through the pulmonary artery and a reduction in left-sided preload and subsequent cardiac output in addition to the primary potential symptom of hypoxia. A leaking or ruptured aortic dissection can also diminish cardiac output through induction of hypovolemia or tamponade (if aortic contents extend into the pericardium). Aortic dissection can induce myocardial infarction when the dissection extends into the coronaries supplying vital portions of the myocardium. When cardiac tissue damage is present along with the conduction system, conduction blocks and other arrhythmias can result. Infarction of valves or chordae tendineae can lead to valve rupture, resulting in subsequent mechanical obstruction to forward flow or induction of retrograde blood flow. Infarcted or ischemic ventricular tissue will have impaired contractility. Obstructive pathologies, such as aortic stenosis, tumors, tamponade, and congenital hypertrophic cardiomyopathy can all follow this pathway, as can myocardial infarction and ischemia. This is in addition to the primary structural problem of the impeded forward blood flow. The increase in pressure can stimulate mechanoreceptors and induce a vagal response and secondary hypotension and bradycardia. The increase in size leads to ventricular myocyte irritability, which can potentially induce arrhythmias. A chronic obstruction to forward blood flow out of the heart will lead to an increase in ventricular size and pressure. Mechanical obstructions to blood flow and cardiac output will have similar effects but through multiple possible mechanisms. Tachyarrhythmias force the heart to pump so fast that it lacks an adequate diastolic phase, leading to ineffective ventricular filling and reduced cardiac output. Bradyarrhythmias lead to this final pathway because the heart is too slow to generate enough flow. When the heart fails to generate adequate cardiac output, the brain is inadequately perfused and temporarily malfunctions, leading to the syncopal event. Īll cases of cardiac syncope have the same general mechanism. For this reason, it is imperative for all healthcare providers to have a general understanding of cardiac syncope and how to recognize it. Distinguishing cardiac syncope from the myriad of other syncopal etiologies can be challenging. Cardiac syncope is estimated to be the cause of syncope in 15% of syncopal events. This cardiac problem may be a rhythm disturbance, a structural problem, or a structural problem that predisposes a patient to a rhythm disturbance. Cardiac syncope occurs when the source of one's loss of consciousness stems from a problem in the heart that prevents it from supplying enough nutrients and oxygen to the brain. While most syncopal events are innocuous, cardiac syncope is often indicative of a potentially fatal, underlying disease process, carrying a one-year mortality rate of 30%. Causes of syncope range widely, including vasovagal, neurologic, metabolic, pulmonary, volume depletion, and cardiac. Syncope, a sudden, transient loss of consciousness and postural tone, is a phenomenon estimated to affect 30% to 40% of the population, and those numbers are likely underestimated given the high prevalence of patients with syncope who do not present to a hospital or urgent care setting. Syncope is responsible for 740,000 trips to the emergency department and a quarter of a million hospital admissions each year in the United States alone.
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