Explanation:

Syncope in the setting of prior myocardial infarction (structural heart disease) accompanied by a wide-complex tachycardia strongly suggests ventricular tachycardia. VT is a life-threatening arrhythmia originating from the ventricles. Cannon A waves indicate atrioventricular dissociation, which is common during VT. The hemodynamic instability (unreadable BP, syncope) further supports a diagnosis of VT over SVT with aberrancy, although the latter can sometimes be difficult to distinguish solely on ECG.

Explanation:

Aortic stenosis involves narrowing of the aortic valve, creating a fixed obstruction to blood flow out of the left ventricle. During exertion or periods of increased cardiac demand, the stenotic valve prevents an adequate increase in cardiac output. This limitation can lead to insufficient cerebral perfusion, resulting in syncope. Therefore, syncope due to severe AS is classified as being caused by an obstruction to blood flow.

Explanation:

Transient ST segment depression during an episode of angina (chest pain) is a hallmark sign of myocardial ischemia. Ischemia reflects a temporary imbalance between myocardial oxygen supply and demand, insufficient to cause permanent cell death (infarction). The ST depression typically resolves when the ischemia is relieved (e.g., with rest or nitrates). Lasting less than 5 minutes further supports ischemia over infarction.

Explanation:

The limb leads II, III, and aVF provide an electrocardiographic view of the inferior surface (diaphragmatic aspect) of the left ventricle. ST segment elevation or significant Q waves in these contiguous leads are indicative of myocardial infarction involving the inferior wall.

Explanation:

Orthostatic hypotension is characterized by a drop in blood pressure upon assuming an upright posture. One key cause is an insufficient circulating blood volume (hypovolemia). This can result from conditions such as dehydration or hemorrhage, leading to inadequate venous return and cardiac output when standing, causing symptoms like dizziness or syncope due to reduced cerebral perfusion. While autonomic dysfunction can also cause orthostatic hypotension, inadequate volume is a distinct physiological mechanism.

Explanation:

During exercise, cardiac output needs to increase significantly to meet metabolic demands. In moderate to severe aortic stenosis, the narrowed valve orifice limits the ability of the left ventricle to eject sufficient blood, creating a fixed outflow obstruction. This inability to augment cardiac output leads to inadequate systemic and cerebral perfusion during exertion, causing syncope due to relative systemic hypotension.

Explanation:

Rheumatic heart disease is the most common cause of Mitral Stenosis (MS). MS leads to elevated left atrial and pulmonary venous pressures, causing pulmonary congestion (dyspnea, orthopnea, pulmonary edema with frothy/bloody sputum). Left atrial enlargement from MS frequently leads to Atrial Fibrillation. Chronic severe MS with pulmonary hypertension can cause low cardiac output and peripheral cyanosis, sometimes manifesting as dusky cheeks (mitral facies). This constellation of findings points strongly to severe Mitral Stenosis.

Explanation:

The combination of muffled heart sounds, elevated JVP, and hypotension (Beck's triad) following significant chest trauma strongly suggests cardiac tamponade. This life-threatening condition occurs when fluid (often blood, post-trauma) accumulates rapidly in the pericardial sac, compressing the heart chambers and severely impairing diastolic filling and cardiac output, leading to obstructive shock.

Explanation:

Dyspnea, particularly Paroxysmal Nocturnal Dyspnea (PND), results from elevated pulmonary venous pressure leading to pulmonary congestion. Mitral valve disease (stenosis or regurgitation) can impair left ventricular filling or increase left atrial pressure, leading to a backup of pressure into the pulmonary circulation. This pathophysiology is characteristic of left-sided heart failure, causing symptoms like exertional dyspnea and PND.

Explanation:

This clinical triad (hypotension, distended neck veins, muffled heart sounds) following chest trauma is highly suggestive of cardiac tamponade. Rapid accumulation of fluid or blood in the pericardial space restricts cardiac filling, leading to decreased stroke volume, low cardiac output, and obstructive shock. It requires urgent recognition and intervention.

Explanation:

While significant Q waves indicate electrically silent, necrotic myocardial tissue and are often seen in completed transmural infarctions, they are not required for the diagnosis of all MIs. Non-Q wave infarctions, particularly those that are subendocardial or non-transmural, may present with only ST segment or T wave changes along with clinical evidence and biomarker elevation. Stable angina is exertional chest pain due to transient ischemia. ST elevation signifies acute transmural injury, while ST depression suggests subendocardial ischemia/infarction. ECG changes characteristically evolve following an acute MI.

Explanation:

The defining feature of orthostatic (postural) hypotension is the symptomatic drop in blood pressure that occurs upon transitioning to an upright position (standing). The symptoms, typically dizziness or lightheadedness, are due to transient cerebral hypoperfusion and characteristically resolve upon returning to a sitting or supine position.

Explanation:

Mitral stenosis obstructs blood flow from the left atrium (LA) to the left ventricle (LV). This leads to increased LA pressure, LA enlargement (predisposing to Atrial Fibrillation and thrombus formation/embolization), and backward transmission of pressure into the pulmonary circulation (causing Pulmonary Edema and Pulmonary Hypertension). However, the obstruction reduces preload on the left ventricle. Consequently, LV failure is typically not a direct complication of isolated mitral stenosis, as the LV is often underfilled rather than overloaded.

Explanation:

The precordial leads V1-V4 primarily reflect the electrical activity of the anterior wall of the left ventricle (with V1-V2 more specifically reflecting the anteroseptal region). ST segment elevation in these leads signifies acute injury to the anterior myocardium. Leads II, III, and aVF view the inferior wall; ST depression in these leads represents reciprocal changes, further supporting an anterior infarction.

Explanation:

Anti-hypertensive medications lower blood pressure, which can sometimes lead to an excessive drop upon standing (postural or orthostatic hypotension). Elderly patients often have less responsive baroreflexes and may be more susceptible to dehydration or taking multiple medications, increasing their risk of falls and injury due to drug-induced postural hypotension.