Coronary Arteries and their Supply to Cardiac Conduction System

The heart’s conduction system is responsible for regulating the heartbeat. The following are the coronary arteries that supply blood to the different parts of the cardiac conduction system:

Sinoatrial Node
The sinoatrial node, which is the primary pacemaker of the heart, is supplied by the right coronary artery in 60% of cases through a sinoatrial nodal branch.

Atrioventricular Node
The atrioventricular node, which is responsible for delaying the electrical impulse before it reaches the ventricles, is supplied by the right coronary artery in 80% of individuals through the atrioventricular nodal branch.

Atrioventricular Bundle
The atrioventricular bundle, which conducts the electrical impulse from the atria to the ventricles, is supplied by numerous septal arteries that mostly arise from the anterior interventricular artery, a branch of the left coronary artery.

Left Bundle Branch
The left bundle branch, which conducts the electrical impulse to the left ventricle, is supplied by numerous subendocardial bundle arteries that originate from the left coronary artery.

Right Bundle Branch
The right bundle branch, which conducts the electrical impulse to the right ventricle, is supplied by numerous subendocardial bundle arteries that originate from the right coronary artery.

Common Causes of Infective Endocarditis and their Characteristics

Infective endocarditis is a serious condition that can lead to severe complications if left untreated. The most common causative organism of acute infective endocarditis is Staphylococcus aureus, especially in patients with risk factors such as prosthetic valves or intravenous drug use. Symptoms and signs consistent with infective endocarditis include fever, heart murmur, and arthritis, as well as pathognomonic signs like splinter hemorrhages, Osler’s nodes, Roth spots, Janeway lesions, and petechiae.

Group B streptococci is less common than Staphylococcus aureus but has a high mortality rate of 70%. Streptococcus viridans is not the most common cause of infective endocarditis, but it does cause 50-60% of subacute cases. Group D streptococci is the third most common cause of infective endocarditis. Pseudomonas aeruginosa is not the most common cause of infective endocarditis and usually requires surgery for cure.

In summary, knowing the characteristics of the different causative organisms of infective endocarditis can help in the diagnosis and treatment of this serious condition.

Management of ST Elevation Myocardial Infarction in Remote Locations

ST elevation myocardial infarction (STEMI) is a medical emergency that requires prompt treatment. Percutaneous coronary intervention (PCI) is the gold standard first-line treatment for STEMI, but in remote locations, the patient may need to be taken to the nearest facility for initial assessment prior to transfer for PCI. In such cases, the most appropriate management strategy should be considered to minimize time delays and optimize patient outcomes.

Administer Thrombolysis and Transfer for PCI

In cases where the transfer time to the nearest PCI facility is more than 120 minutes, fibrinolysis prior to transfer should be strongly considered. This is particularly important for patients with anterior STEMI, where time is of the essence. Aspirin, clopidogrel, and low-molecular-weight heparin should also be administered, and the patient should be transferred to a PCI-delivering facility as soon as possible.

Other Treatment Options

If PCI is not likely to be achievable within 120 minutes of when fibrinolysis could have been given, thrombolysis should be administered prior to transfer. Analgesia alone is not sufficient, and unfractionated heparin is not the optimum treatment for STEMI.

Conclusion

In remote locations, the management of STEMI requires careful consideration of the potential time delays involved in transferring the patient to a PCI-delivering facility. Administering thrombolysis prior to transfer can help minimize delays and improve patient outcomes. Aspirin, clopidogrel, and low-molecular-weight heparin should also be administered, and the patient should be transferred to a PCI-delivering facility as soon as possible.

Lachmann test

Management of Narrow Complex Supraventricular Tachycardia

When a patient presents with narrow complex supraventricular tachycardia, the initial management would be to administer IV adenosine, provided there are no contraindications such as asthma. This medication creates a transient conduction delay, which may terminate the tachycardia or slow down the heart rate enough to identify the underlying rhythm. This information is crucial in determining the optimal antiarrhythmic therapy for the patient.

However, if the patient experiences chest pain, hypotension, SBP <90 mmHg, or evidence of cardiac failure, then DC cardioversion would be necessary. It is important to note that if the patient is not haemodynamically compromised, IV adenosine is the preferred initial management for narrow complex supraventricular tachycardia. By following these guidelines, healthcare professionals can effectively manage this condition and provide the best possible care for their patients.

Common Cardiovascular Abnormalities Associated with Genetic Syndromes

Various genetic syndromes are associated with cardiovascular abnormalities. Turner syndrome is linked with coarctation of the aorta, aortic stenosis, bicuspid aortic valve, aortic dilation, and dissection. Marfan syndrome is associated with aortic root dilation, mitral valve prolapse, mitral regurgitation, and aortic dissection. Kartagener syndrome can lead to bicuspid aortic valve, dextrocardia, bronchiectasis, and infertility. However, congenital adrenal hyperplasia is not associated with congenital cardiac conditions. Finally, congenital rubella syndrome is linked with patent ductus arteriosus, atrial septal defect, and pulmonary stenosis.

Differentiating Heart Murmurs and Symptoms

Tricuspid regurgitation is characterized by signs of right heart failure, such as dyspnea and peripheral edema, and a classical murmur. The backflow of blood to the right atrium leads to right heart dilation, weakness, and eventually failure, resulting in ascites and poor ejection fraction causing edema.

Mitral regurgitation has a similar murmur to tricuspid regurgitation but is heard best at the apex.

Aortic regurgitation is identified by an early diastolic decrescendo murmur at the left sternal edge.

Aortic stenosis does not typically result in ascites, and its murmur is ejection systolic.

Pulmonary stenosis is characterized by a mid-systolic crescendo-decrescendo murmur best heard over the pulmonary post and not a holosystolic murmur at the left sternal edge.

Understanding Heart Murmurs and Symptoms

During embryonic development, the septum primum grows down from the roof of the primitive atrium and fuses with the endocardial cushions. It initially has a hole called the ostium primum, which closes as the septum grows downwards. However, a second hole called the ostium secundum develops in the septum primum before fusion can occur. The septum secundum then grows downwards and to the right of the septum primum and ostium secundum. The foramen ovale is a passage through the septum secundum that allows blood to shunt from the right to the left atrium in the fetus, bypassing the pulmonary circulation. This defect closes at birth due to a drop in pressure within the pulmonary circulation after the infant takes a breath. If there is overlap between the foramen ovale and ostium secundum or if the ostium primum fails to close, an atrial septal defect results. This defect does not cause cyanosis because oxygenated blood flows from left to right through the defect.

Differential Diagnosis for a Patient with Hypotension, Tachycardia, and Muffled Heart Sounds Following a Road Traffic Accident: Cardiac Tamponade, Myocarditis, NSTEMI, Pericarditis, and STEMI

A 67-year-old man presents with hypotension, tachycardia, and poor peripheral perfusion following a road traffic accident with a steering wheel injury. On examination, muffled heart sounds and pulsus paradoxus are noted, and an ECG shows widespread anterior T-wave inversion. The patient has a history of inferior wall MI seven years ago. Arterial blood gas analysis reveals respiratory acidosis.

The differential diagnosis includes cardiac tamponade, myocarditis, NSTEMI, pericarditis, and STEMI. While myocarditis can cause similar symptoms and ECG changes, the presence of muffled heart sounds and pulsus paradoxus suggests fluid in the pericardium and cardiac tamponade. NSTEMI and STEMI can also cause acute onset of symptoms and ECG changes, but the absence of ST elevation and the history of trauma make cardiac tamponade more likely. Pericarditis can cause muffled heart sounds and pulsus paradoxus, but the absence of peripheral hypoperfusion and the presence of non-specific ST-T changes on ECG make it less likely.

In conclusion, the clinical scenario is most consistent with traumatic cardiac tamponade, which requires urgent echocardiography for confirmation and possible guided pericardiocentesis.

Management of Chest Pain in a Patient with Risk Factors for Cardiac Disease

Chest pain is a common presenting complaint in primary care and emergency departments. However, it is important to consider the possibility of an acute coronary syndrome in patients with risk factors for cardiac disease. Here are some management strategies for a patient with chest pain and risk factors for cardiac disease:

Arrange a 12-h troponin T assay before deciding whether or not to discharge the patient. A normal troponin assay would make a diagnosis of acute coronary syndrome unlikely, but further investigation may be required to determine if the patient has underlying coronary artery disease.

Do not discharge the patient with a diagnosis of costochondritis based solely on chest wall tenderness. This should only be used in low-risk patients with tenderness that accurately reproduces the pain they have been feeling on minimal palpation.

Do not discharge the patient if serial resting ECGs are normal. A normal ECG does not rule out an acute cardiac event.

Admit the patient to the Coronary Care Unit for monitoring and further assessment only if the 12-h troponin comes back elevated.

Do not discharge the patient and arrange an outpatient exercise tolerance test until further investigation has been done to rule out an acute cardiac event.

In summary, it is important to consider the possibility of an acute coronary syndrome in patients with chest pain and risk factors for cardiac disease. Further investigation, such as a 12-h troponin assay, may be required before deciding on appropriate management strategies.