On the Cardiology ward, there are two individuals. One of them is 75 year old Antonia, who’s complaining of chest pain and says she hardly catches her breath after walking. On clinical examination, her pulse feels pretty weak and on auscultation, a systolic murmur is heard. The murmur was louder just after S1 and got quieter and quieter by the end of S2.
The other individual is 38 year old Mark who has a history of rheumatic fever and is complaining of not being able to swallow properly. On clinical examination, his voice sounds raspy and on auscultation, a snap is heard after S2 along with a diastolic rumble. Based on auscultation, both individuals were sent for echocardiography.
Okay, so based on auscultation and symptoms, both individuals seem to have valvular heart disease. Valvular heart disease involves damage or a defect in one or more of the four valves of the heart, so the aortic and mitral valves on the left side of the heart, and the pulmonary and tricuspid valves on the right side of the heart.
Okay, now, before talking specifics about valvular disease, we’ll first talk about rheumatic fever, which can affect multiple valves. Rheumatic fever can develop after streptococcal infection like strep throat, which is caused by Streptococcus pyogenes. This particular group of streptococcus has an antigen that lumps it into a group called “group A”, and they also produce an enzyme called streptolysin, which causes hemolysis. Some of these strep bacteria have a protein on their cell wall called “M protein”, and this particular protein is highly antigenic, meaning that the immune system sees it and recognizes it as a foreign molecule and produces antibodies against it.
Now, this becomes a problem when these antigens cause a phenomenon called molecular mimicry. M proteins can be structurally similar to human proteins, which means the antibodies that target them will also target our own tissue. In this case, they are similar to proteins found in the myocardium and heart valves. Once bound to cardiac tissue, the antibodies activate nearby immune cells, which causes a cytokine-mediated inflammatory response and tissue destruction. This is also an example of what’s called a type 2 hypersensitivity reaction.