Heart Anatomy

Understanding heart anatomy is fundamental for nearly every cardiology and emergency medicine scenario you'll face in finals and clinical practice. From interpreting ECGs and localising myocardial infarctions to understanding heart sounds and valvular disease, a solid grasp of the heart's structure, its blood supply, and electrical conduction system is non-negotiable. This topic underpins your ability to diagnose and manage common and life-threatening cardiac conditions.

The heart's intricate structure is a direct result of its embryological development, with each chamber and valve designed for efficient blood flow. The right atrium features the crista terminalis, a muscular ridge marking the embryonic junction of the sinus venosus and primitive atrium, and the pectinate muscles, which are rough muscular ridges. The right ventricle is characterised by the moderator band (septomarginal trabecula), a muscular band carrying part of the right bundle branch to the anterior papillary muscle – a key landmark in OSCEs. The left ventricle's wall is significantly thicker (approx. 3:1 ratio compared to the right) to generate the high pressures needed for systemic circulation. Cardiac muscle cells (myocytes) are interconnected by intercalated discs, facilitating rapid electrical impulse propagation. Coronary arteries, arising from the aortic sinuses, fill predominantly during diastole when the aortic valve is closed and the aorta recoils. The LAD artery, often called the 'widow maker', supplies the anterior two-thirds of the interventricular septum and the apex, making it critical for left ventricular function.

Understanding coronary anatomy is vital for localising myocardial infarctions (MIs): LAD occlusion causes anterior/septal MIs (V1-V4 changes), RCA occlusion causes inferior MIs (II, III, aVF changes), and circumflex occlusion causes lateral/posterior MIs (I, aVL, V5, V6 changes, or V1-V2 reciprocal changes). Valvular heart disease, such as mitral stenosis or aortic regurgitation, produces characteristic murmurs detected on auscultation, requiring knowledge of valve locations and normal blood flow. Pericarditis can lead to pericardial effusion and potentially life-threatening cardiac tamponade, classically presenting with Beck's triad (hypotension, raised JVP, muffled heart sounds). Atrial fibrillation often originates from ectopic foci near the pulmonary vein ostia, highlighting the anatomical relationship. Recognising these anatomical associations is crucial for interpreting ECGs, echocardiograms, and clinical presentations.

An ECG provides crucial information about the heart's electrical conduction system and can localise ischaemia/infarction based on lead changes corresponding to specific coronary territories. Echocardiography (Transthoracic TTE or Transoesophageal TOE) is the primary imaging modality for assessing cardiac chamber size, wall motion, valvular function, and ejection fraction. Coronary angiography (cardiac catheterisation) remains the gold standard for visualising coronary artery stenosis. Cardiac MRI offers detailed structural and functional assessment, including myocardial viability. CT Coronary Angiography (CTCA) provides non-invasive imaging of the coronary arteries, useful for ruling out coronary artery disease.

Acute management of myocardial infarction focuses on rapid reperfusion, either via percutaneous coronary intervention (PCI) or thrombolysis, depending on local protocols and presentation time. Heart failure management involves optimising cardiac output and reducing symptoms with medications like ACE inhibitors, beta-blockers, and diuretics. Valvular heart disease may require surgical repair or replacement, or transcatheter interventions. For anatomy, the focus is on identifying structures during procedures (e.g., cannulation of coronary ostia, valve repair/replacement).