How The Heart Works

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10 min 46 sec
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Understanding the Heart: Function and Implications

Introduction to Cardiac Function

In this educational video, we delve into the intricate workings of the heart. The heart, positioned centrally within the adult chest with a slight leftward bias, comprises four chambers filled with blood. These chambers are divided into left and right sides, each serving distinct circulatory functions. The heart's unique physiology involves countless tiny myocytes, generating electrical impulses that orchestrate sequential contractions, propelling blood in a unidirectional flow. Essential valves regulate these processes, responding to chamber pressures.

The Cardiac Electrical Conduction System

The heart's electrical conduction system commences with the Sinoatrial Node (SA Node), often referred to as the pacemaker of the heart. This node, under nervous system control, initiates electrical impulses. The impulse then travels across the atria, reaching the Atrioventricular (AV) Node. The AV node slows the impulse to allow blood passage from the atria to the ventricles, coordinating this flow via atrioventricular valves. Subsequently, the signal proceeds through the Bundle of His into the left and right bundle branches, ultimately activating the Purkinje Fibres. This prompts a wave of depolarization, causing ventricular muscle contractions and blood ejection into both pulmonary and systemic circulations.

Heart Rate Regulation

The heart's rhythm is typically controlled by the vagus nerve, adjusting the rate to maintain blood pressure and organ perfusion. Systemic issues, such as shock, fever, or hypothermia, can disrupt this nervous control. In cases of tachycardias and bradycardias, it's crucial to differentiate between intrinsic and extrinsic causes. Recording an ECG rhythm assists in this determination.

Supraventricular Tachycardias

Supraventricular tachycardias, often resulting from intrinsic factors, can lead to heart rates exceeding 200 beats per minute. This increased rate hampers ventricular filling, reducing cerebral perfusion and blood pressure. Management involves simulating increased vagal influence, achieved by applying pressure to the carotid sinus. If unsuccessful, medications like Adenosine are administered. Amiodarone may be used for broader complex rhythms. If all else fails, electrical cardioversion may be necessary.

Cardiac Ischemia and Arrhythmias

Cardiac ischemia can disrupt the electrical conduction system, leading to arrhythmias. Re-entry tachycardias can result from hypoxic conditions, causing rapid impulses. As heart rate increases, ventricular filling time decreases, potentially causing shock symptoms. Managing supraventricular tachycardias involves mimicking increased vagal influence, medication administration, and, in severe cases, electrical cardioversion.

Summary of Cardiac Blood Flow

In summary, blood enters the heart through the right atrium, is pumped into the right ventricle, and then directed to the pulmonary circulation for oxygenation. Oxygen-rich blood returns via the left atrium, enters the left ventricle, and is ejected into the systemic circulation, supplying organs throughout the body. This intricate process maintains essential oxygen and nutrient delivery to body tissues.