The Circulatory System and the Heart

• The circulatory system delivers oxygen, nutrients, and other substances to cells. It removes waste products of cellular metabolism.

The Heart

• The heart pumps blood through two separate circulatory systems.
• Pulmonary circulation occurs in the right heart to the lungs.
• Systemic circulation occurs in the left heart to the rest of the body.
• Arteries carry blood away from the heart and branch to form smaller vessels which become capillaries.
• Capillaries allow the closest contact between the blood and the interstitium.
• Veins channel blood from capillaries in all parts of the body back to the heart.
• The lymphatic system returns excess tissue fluid back to the bloodstream.

Heart Wall Layers

• Pericardium is the membranous sac that encloses the heart.
• Myocardium is the heart muscle.
• Endocardium is the internal lining.
• The heart has four chambers: right and left atria, and right and left ventricles.
• The right and left atria are smaller and have thinner walls.
• The right and left ventricles have a thicker myocardial layer.
• Valves of the heart allow one-way blood flow through the heart.
• Tricuspid: right atrioventricular valve.
• Mitral: left atrioventricular valve.
• Pulmonary: valve.
• Aortic: valve.

The Cardiac Cycle

• The pumping action of the heart consists of contraction and relaxation of the myocardial layer of the heart wall.
• Each contraction and the following relaxation constitutes one cardiac cycle, the "heart beat."
• Diastole is the relaxation phase where blood fills the ventricles.
• Systole is the contraction phase that propels blood from the ventricle into the circulation.
• The left ventricle contracts slightly earlier than the right ventricle.

Phases of Cardiac Cycle

• Systole begins with 'isometric contraction,' with a constant ventricular volume, the first detectable rise in ventricular pressure.
• When left ventricular pressure reaches that of the aorta, the aortic valve opens and ventricular ejection occurs. Intraventricular pressure and volume decrease rapidly.
• With ventricular relaxation and decreased ventricular pressure, the aortic valve closes and isovolumic relaxation occurs.
• When sufficient decreases exist in left ventricular pressure, the mitral valve opens and ventricular filling from the atrium occurs.

Basic Electrophysiology

• The continuous, rhythmic repetition of the cardiac cycle depends on the transmission of electrical impulses (cardiac action potentials) through the myocardium.
• It stimulates the fibers to shorten causing muscular contraction, known as Systole.
• The myocardium contains its own conduction system, which contains specialised cells at certain sites called nodes.
• Conduction system:
  • Sinoatrial (SA) node: Electrical impulses arise in the (SA node). Referred to as the pacemaker of the heart.
  • The SA node is located at the junction of the right atrium and the superior vena cava and lies approximately 1 mm below the visceral pericardium.
  • Beginning systole: action potentials generated in the SA node travel through pathways in atrial myocardium causing both atria to contract.
  • The action potential is transmitted from atrial to ventricular myocardium through fibers of the conduction system.
  • Atrioventricular node (AV) – AV bundle - bundle branches of the interventricular septum - Purkinje fibers in the heart wall.
  • Ventricular activation occurs sequentially in 3 phases; septal activation, apical activation, basal (upper) and posterior activation.

Cardiac Action Potentials

• Depolarisation is electrical activation of the muscle cells caused by movement of electrically charged ions across cardiac cell membranes
• The inside of the cell becomes negatively charged during depolarisation.
• Repolarisation is the deactivating of the muscle cells in the same way as depolarisation.
• Membrane potential: Electrical voltage across the cell membrane caused by the movement of ions in and out of the cell.
• The phases of the cardiac action potential are related to changes in the permeability of the cell membrane, primarily sodium (Na) and potassium (K).
• Normal myocardial cell depolarisation occurs in 5 phases;
  • Phase 0: depolarisation, rapid Na entry into the cell.
  • Phase 1: early repolarisation, slow Calcium (Ca) entry.
  • Phase 2: continuation of repolarisation slow entry of Na and Ca.
  • Phase 3: K is moved out of the cell.
  • Phase 4: return to resting membrane potential.
• The phases of depolarisation and repolarisation occur differently in the SA and AV node cells enabling the generation of independent cardiac action potentials.

The Electrocardiogram (ECG)

• The ECG is recorded from skin electrodes and is the sum of all the cardiac action potentials.
• P wave represents atrial depolarisation.
• PR interval: Is measure of time from the onset of atrial activation to the onset of ventricular activation.
• Represents the time to travel from SA node through the atrium (AV) and bundle and Purkinje system to activate ventricular myocardial cells.
• QRS complex represents the sum of all ventricular myocardial depolarisations.
• ST interval: The interval between ventricular depolarization and repolarization.
• QT interval: Represents the time of ventricular activity including both depolarization and repolarization. It is measured from the beginning of the QRS complex to the end of the T wave. The QT interval will vary with patient gender, age and heart rate.

The Great Vessels

• The right heart receives venous blood from the systemic circulation via the superior vena cava (SVC) and inferior vena cava (IVC) into the right atrium.
• Blood leaves the right ventricle and enters the pulmonary artery.
• The pulmonary artery divides into the right and left pulmonary arteries to transport de-oxygenated blood to the lungs.
• Four pulmonary veins, two from each side, transport oxygenated blood from the lungs to the left atrium.
• The blood moves through the left atrium and ventricle to the aorta.

The Coronary Arteries

• Left Coronary Artery arises behind the left cusp of the aortic valve.
• Branches into the left anterior descending artery (LAD) and the circumflex artery (LCX).
• LAD delivers blood to portions of the left and right ventricles and much of the interventricular septum.
• Travels down the anterior surface of the interventricular septum towards the apex of the heart.
• LCX travels down a groove called the coronary sulcus to the left border of the heart. It supplies blood to the left atrium and the lateral wall of the left ventricle.
• Right Coronary Artery arises behind the right aortic cusp.
• Extends round the right heart to the hearts posterior surface, where it branches to the atrium and ventricle
• Three major branches: conus, marginal branch, posterior descending artery or branch (PDA).
• Coronary Vein: Blood from the coronary artery drains into the cardiac veins, which travel alongside the arteries.
• The veins feed into the cardiac vein and then the coronary sinus on the posterior surface of the heart.
• Venous coronary blood empties into the right atrium.

Coronary Angiogram

• A minimally invasive procedure to access the coronary circulation.
• A cardiac catheter is introduced into the coronary arteries via arterial access at a more peripheral site, commonly the femoral artery.
• Iodinated contrast is injected into the vessel and images are recorded using fluoroscopy.
• Fluoroscopy is a diagnostic technique using x-rays for 'real-time' imaging and recording of the anatomy.
• Visualizes the dynamics of the organ or body part.
• The vessels fill with contrast; the lumen of the vessel is visualised and any narrowing or blockages are characterised.
• Used for both diagnostic and treatment purposes.

CT Coronary Angiography

• It's a non invasive diagnostic examination of the coronary arteries. Patient is fasted and beta blockers are given to reduce the heart rate to approximately 60 beats per minute.
• Nitroglycerine is administered orally to dilate the coronary vessels
• Intravenous iodinated contrast is administered peripherally and the contrast bolus is until tracked until the desired density is reached
• Scan is also ECG gated. The data is acquired when cardiac motion is minimal, preferably in the mid-diastolic phase.
• Data is then reformatted to give curved planar and 4D volume rendered images.

Arteries

• Blood vessels that carry blood away from the heart.
• Most arteries carry oxygenated blood, but the pulmonary and umbilical arteries are exceptions.
• Have a higher blood pressure than other parts of the circulatory system generated by the forceful contractions of the heart's left ventricle. Arteries branch into arterioles that further branch into the smallest vessels, the capillaries.
• Consists of 3 layers:
  • Tunica adventitia: The outermost layer is comprised of connective tissue anchoring arteries to nearby tissues.
  • Tunica media: It is made up of smooth muscle cells and elastic tissue, maintains blood pressure.
  • Tunica intima: The innermost layer is in direct contact with the flow of blood lined with endothelial cells.
  • Lumen: The hollow internal cavity in which the blood flows

The Aorta

• It is the root systemic artery with its origin at the left ventricle via the aortic valve.
• Generally divided into 3 portions: ascending, the arch and the descending aorta.
• Anatomical reference: Thoracic / abdominal aorta divided at the aortic hiatus of the diaphragm.
• The coronary arteries are very first branches off the aorta.

Veins

• Veins transport de-oxygenated blood from the venules in the capillary bed back to the heart.
• Thin walled and fibrous with a larger diameter.
• More numerous.
• Tunica externa has less elastic tissue and does not recoil after distension as quickly as arteries.
• Contain valves, particularly the extremities, to prevent backflow.
• The valves are folds of tunica intima and resemble to valves of the heart.

The Respiratory System

• Consists of upper and lower airways
• Lungs: upper, middle, and lower lobes on the right; upper and middle lobes on the left
• Chest wall (thoracic cage)
• Pulmonary circulation
• Mediastinum contains the heart, the greater blood vessels, and the oesophagus
• Function: Exchange of gases between environmental air and the blood
• Ventilation: ventilate the alveoli
• Diffusion: Diffuse gases in and out of the blood
• Perfusion: Perfuse the lungs so that the organs and tissues receive blood rich in O2 and low in CO2.
• Arteries
• Veins

Upper Respiratory Tract

• Structure: Nasal cavity, Nasopharynx, Oropharynx, Laryngopharynx,Larynx.
• Allows for passage of air in and out of the lower respiratory tract
• Lined with ciliated mucosa with very rich blood supply Warms and humidifies the air and removes foreign particles
• The larynx connects the upper and lower airways

Lower Respiratory Tract

• Trachea connects the larynx to the bronchi.
• Segmental bronchi: trachea divides into two main airways at the carina.
  • Right main bronchus extends more vertically than the left. The right and left main bronchi enter the lungs at the hila.
• Lobar bronchi - segmental - subsegmental.
• Terminal bronchioles: Smallest of the conducting airways.
• Gas exchange airways such as respiratory bronchioles; alveolar ducts; and Alveoli Alveoli are the primary gas exchange units of the lung

The Lungs

• Located in the chest cavity on either side of the heart
• Superior border is at the apex Inferior border is at the diaphragm.
• Both lungs have a central recession called the hilum where the blood vessels and airways pass into the lungs
• Lungs are surrounded by the pulmonary pleurae, with the outer parietal pleura lining the inner wall of the rib cage.
• The inner visceral pleura lines the surface of the lungs.
• Pleural cavity is the space between the pleura which contains pleural fluid
• Each lung is divided into lobes by the invaginations of the pleura as fissures.
• The fissures are double folds of pleura that section the lungs and help in their expansion.
• The right lung has three lobes (upper, middle and lower) and the left lung has two lobes (upper and lower).

The Chest X-Ray

(PA)

• Includes: Lung pleura, Heart (Left ventricle), Thoracic spine, Trachea, Aorta (arch), Carina/hilum, Right atrium, Left atrium, Right costophrenic angle, Left hemi-diaphragm, 4th posterior right rib, Left clavicle, and Right sterno-clavicular joint.

The Chest X-Ray

(Lateral)

• Includes: Trachea, Oesophagus, Heart, Thoracic spine, Right Diaphragm, Left Diaphragm, Hilar region, Right rib, Anterior costophrenic angle, Posterior costophrenic angle, Body of sternum and Scapula.

Arch of the Aorta

• The aortic arch curves above the heart between the ascending and descending aorta.
• All of the blood delivered from the heart to the systemic tissues of the body passes through the aorta.
• The ascending aorta turns 180 degrees towards the body's left side in the aortic arch.
• From the arch the aorta passes posterior to the heart and descends through the thorax and abdomen as the descending aorta.
• Three major arteries branch off from the superior arterial wall of the aortic arch to supply blood to the tissues of the superior regions of the body:
  • The brachiocephalic trunk: the first artery to arise from the aortic arch, carrying blood to the right arm and the right side of the head and neck.
  • The left common carotid artery supplies blood to the left side of the head and neck.
  • The left subclavian artery arises from the aortic arch and supplies blood to the left arm.

Venous Return Superior to the Heart

• The superior vena cava (SVC) is a large valveless venous channel formed by the union of the brachiocephalic veins.
• Receives blood from the upper half of the body and returns it to the right atrium.
• The brachiocephalic vein (innominate vein): Returns deoxygenated blood from the upper limbs, neck, and head
• The two brachiocephalic veins merge together with the azygous vein, which carries deoxygenated blood from the rib cage, to form the superior vena cava
• The subclavian veins (SCV): The major venous channel that drains the upper limb.
• The subclavian vein starts at the crossing of the lateral border of the 1st rib. It receives only one tributary, the external jugular vein, before joining the internal jugular vein posterior to the sternoclavicular joint, where it forms the brachiocephalic vein.

Coronary Artery Disease/Myocardial Ischemia

• Impaired pumping ability of the heart due to depriving the heart muscle of blood-borne oxygen.
• The most common cause of coronary obstruction is atherosclerosis.
• Arteriosclerosis is a chronic disease of the arterial system characterised by abnormal thickening and hardening of the vessel walls.
• Atherosclerosis is an inflammatory disease in which the thickening and hardening is caused by an accumulation of lipid-laden macrophages, that leads to the formation of a lesion called plaque. Diminished myocardial blood supply leads to ischemia - the cells remain alive but cannot function normally.
• Complete occlusion of the coronary artery causes infarction or the death of the myocardial tissue (heart attack).
• Risk factors include advanced age, gender, family history (non-modifiable). or Dyslipidemia (elevated lipid plasma proteins), hypertension, cigarette smoking, diabetes, obesity, sedentary life-style (modifiable).

Myocardial Perfusion Scintigraphy (MPS)

• An excellent prognostic tool that identifies high-risk patients for infarction.
• Can predict the effectiveness of therapy & evaluate the effectiveness of revascularisation
• Can be used for pre-surgical work-up in at-risk patients and assess coronary artery disease
• Helps Identify and differentiates myocardial ischemia from myocardial infarction
• Ischemia can be treated; infarction requires management
• Uptake of the radiopharmaceutical in the myocardium is directly proportional to the coronary blood flow at the time of administration
• After a patient undergoes stress-test, they are administered 99mTc Sestamibi at peak exercise and then imaged using SPECT.
• Images are displayed in three planes: Short Axis, Horizontal Long Axis, Vertical Long Axis
• Following post-stress imaging, the patient is re administered another dose of 99mTc Sestamibi at rest, then undergoes rest imaging.
• The acquired data is processed in short axis, horizontal long axis, and vertical long axis planes. The stress and rest images are then aligned to each other for display, and perfusion defects in both rest and stress slices are noted.
• Fixed [non-reversible] defect in the inferior wall noted at both rest and stress in short axis (SAX) slices is a diagnostic indicator of Myocardial Infarction.

Cor Pulmonale

• Right ventricular enlargement, secondary to pulmonary hypertension caused by disorders of the lungs.
• Pulmonary hypertension creates chronic pressure overload in the right ventricle, causing hypertrophy of the normally thin walled right ventricle.
• Diagnosis is made on the basis of physical examination, ECG, and X-Ray.
• There is no curative treatment; medical therapies dependant on reversal of underlying lung disease.

Pleural Effusion

• Pleural effusion is the presence of fluid in the pleural space.
• Fluids that accumulate in the lung can cross into the pleural space, and include transudative, exudative, empyema, haemothorax and chylothorax.

Chronic Obstructive Airway Disease (COAD)

• A disease of the lungs where the airways become narrowed. Causes a limitation of airflow to and from the lungs and causes shortness of breath.
• Caused by noxious particles or gas which triggers an abnormal inflammatory response in the lung.
• The most common obstructive diseases are asthma, chronic bronchitis and emphysema
• Asthma is a chronic inflammatory disorder of the airways.
• Chronic bronchitis is defined as the hypersecretion of mucus and a chronic cough that continues for at least 3 months of the year.
• Emphysema is abnormal permanent enlargement of the gas exchange airways accompanied by the destruction of alveolar walls.

Chronic Obstructive Airway Disease (COAD)

• Causes include: smoking, occupational exposures, air pollution, and genetics
• Symptoms: dyspnoea, persistent cough, sputum and mucus production, wheezing, chest tightness, respiratory failure
• Diagnosis:
• Spirometry measures the forced expiratory volume in 1 second (FEV1) as well as the greatest volume of air that can be expelled in 1 whole large breath (Forced Vital Capacity FVC)
• Chest X-ray and High Resolution CT (HRCT) 1mm thin slices help show lung hyperinflation, and the extent and distribution of emphysema and bullae formation

Pneumothorax

• Presence of air or gas in the pleural space caused by a rupture in the visceral pleura, or the parietal pleura and the chest wall
• The negative pressure of the pleural space is disrupted causing the lung to collapse
• Communicating pneumothorax: barometric pressure is equal between inspiration and expiration
• Tension pneumothorax: Plural rupture acts as one way valve (permitting air to enter on respiration but preventing escape).
• Spontaneous pneumothorax: spontaneous rupture of blebs (blister like formations)
• Secondary pneumothorax: Caused by chest trauma, such as rib fracture, stab wound etc.

Primary Lung Cancer

• Primary lung cancer is a disease of uncontrolled cell growth in the lung. Most lung cancers are carcinomas of the lung, which originate from the epithelial cells.

• There are two main types of lung carcinoma, small cell lung carcinoma, and Non small cell lung carcinoma.

• The most common cause is long term exposure to tobacco smoke, which causes cumulative changes to the DNA in the tissue lining the bronchi of the lung and asbestos.

• Symptoms :Shortness of breath, Haemoptysis (coughing up blood), Chronic coughing, airway wheeze, difficulty in breathing, Chest pain, Weight loss, and fatigue

• Diagnosis : Chest X-ray, CT, CT guided biopsy, Bronchoscopy, Sputum cytology, Thoracoscopic surgery, and Biopsy of other sites

Pulmonary Embolus (PE)

• A blockage of a pulmonary artery or one of its branches (usually from a venous thrombus).
• The thrombus travels to the lung via the venous return to the right heart and into the pulmonary circuit, which is called thrombo-embolism.
• Symptoms include sudden onset dyspnea, tachypnea, pleuritic chest pain, cough, and haemoptysis (severe cases cause death).
• Diagnosis:
  • Blood tests like a D-dimer test that tests for clotting status.
  • Extremity doppler ultrasound with blood flow can be used to detect DVTs. Tests to detect location and extent of embolism via chest xray, CT pulmonary angiogram (CТРА), and Ventilation scan (VQ scan).

V/Q Scan: Ventilation vs Perfusion

• Involves patient breathing in 99mTc Technegas which localises in the alveolar sacs and allows the visualisation of pulmonary ventilation through images taken in multiple projections around the lungs.
• 99mTc MAA [Macroaggregated Albumin] gets administered which lodge in the pulmonary capillaries, and allows pulmonary perfusion to be visualised.
• The images are then displayed side by side for comparison between the ventilation and perfusion images in all projections.
• In a pulmonary embolus (PE), the size of the defect represents the location of the PE itself -- A PE in the arterioles will demonstrate smaller, wedge shaped defects further into the periphery.

Aortic Dissection

• Defined as the separation of the layers within the aortic wall
• Blood penetrates the intima and enters the media layer
• High pressure rips the tissue of the media apart along the laminated plane
• Aortic Dissection has has symptoms of a sudden onset of severe chest pain, Can involve the entire aorta including the carotid , renal , and other arteries.

-Aortic Dissection has diagnosis through with Ultrasound / Computed Tomography / ultrasound / with ultrasound.