HOW I TEACH
Coagulation Made Easy
Here , ASH Clinical News associate editor Alice Ma , MD , shares her advice for teaching the coagulation cascade to hematologists and nonhematologists , medical students , and attendings . Dr . Ma is a professor in the Department of Medicine , Division of Hematology and Oncology , at the University of North Carolina School of Medicine in Chapel Hill .
This article is repurposed from “ How I Teach the Coagulation Cascade ,” which originally appeared in the April 2016 issue of ASH Clinical News . Visit ashclinicalnews . org / how-i-teach-coagulation-cascade to download Dr . Ma ’ s complete presentation to use with your students – or as a refresher for yourself !
Alice Ma , MD
Why is the coagulation cascade such a pain to teach – and to learn ? The first and most obvious problem : Coagulation is written in Roman numerals . Right off the bat , we Arabic numeral – users are at a disadvantage . Next , the factors were numbered in order of their discovery , and not in order of their function ; and , as blood researchers learned more about coagulation , they realized that there is not , in fact , a factor III , or IV , or VI . We thought there was , but there ’ s not .
And , then there is the more frustrating problem : The model of the coagulation cascade helps explain abnormalities in blood clotting – test results , but it does not reflect the patient ’ s biology . If it did , then hemophiliacs shouldn ’ t bleed , factor Xa inhibitors such as low-molecular-weight heparin ( LMWH ) should prolong clotting times , and patients with factor XII deficiency should bleed horribly . In reality , none of these things is true . As one could expect , this infuriates learners . My job , as a medical educator , is to help them out . So , how do I make it a bit easier ? I use simple learning tricks like mnemonics that make the coagulation cascade easier to remember
Enter the “ Coagulation Made Easy ” presentation – complete with mnemonics , visual aids , and simple diagrams . I ’ ve borrowed ( okay , stolen ) bits of this from other smart people and I ’ ve lent it to many others .
Coagulation Made Easy The PTT Pathway The PT Pathway
Factor V is a cofactor for Factor X , and you can remember this because V fits into the notch of the X .
My teaching philosophy is : “ Don ’ t make topics any harder than they need to be .” I like to make things simple and bring them to the level of the trainee . For example , I take advantage of the Roman numerals by teaching learners that “ X ” marks the spot where two pathways converge , and that the point at the bottom of a “ V ” conveniently fits into the cleft at the top of an “ X ”! Who knew ?
Some people might turn their nose up at learning devices like mnemonics but , for a difficult and complicated subject , I say bring it on . Give me something I can jam into my head , and we ’ ll work on the specifics later . Does that make me intellectually lazy ? I hope not , but if it means I can get medical students , fellows , and even orthopedic surgeons to know the coagulation cascade , then I will gladly be called lazy .
The method I developed is practical , hands-on , and – probably its greatest strength – not scientific at all .
Why do I prefer this “ nonscientific ” approach ? Because of the aforementioned stumbling block : The coagulation cascade doesn ’ t make sense in real-life biology .
For example , if there are two equivalent methods for generating factor Xa from factor X – meaning just as much thrombin is produced in factor Xa from factor VII – then why is factor VIII needed on the other side of the cascade ? If the cascade reflected real-life biology , then hemophiliacs shouldn ’ t bleed . And why doesn ’ t factor XII matter ? It leads to a prolonged PTT , but it doesn ’ t have any effect on bleeding .
Another sticking point : When heparin is used , it will block thrombin , inhibit factor Xa , and prolong the PTT and , to a lesser effect – the prothrombin time ( PT ). In a PT assay , heparinase is used , so heparin is degraded , and the effect on PT is understandable . However , this doesn ’ t explain why LMWH does not affect the PT and PTT times . LMWH inhibits thrombin-generating factor X ; without factor X , thrombin is unable to turn fibrinogen into fibrin . Why doesn ’ t that affect the PT and PTT ? Hematology can be hard . How do we break this to students ? Admit that it ’ s a mystery to all of us . Think about it this way : Can I explain the inner workings of my car ’ s internal combustion engine ? Do I know what a carburetor does ? Not really , but I still drive my car . For all intents and purposes , it ’ s a miracle .
For others who want a better and deeper understanding of coagulation , there ’ s the elegant cell-based model of hemostasis outlined by Hoffman and Monroe . 1 It is a beautiful description that helps refine the theory and understanding of coagulation . I use it to explain coagulation to trainees who want more insight into biology .
And , the truth is , this approach works . If my obituary ends up in my local paper , it will be because I have gotten literally tens of thousands of people to understand the coagulation cascade , some of them for minutes at a time . I use this technique for learners at all stages ( medical students , residents , fellows , attendings of all ranks ) and all disciplines ( anesthesia , surgery , OB-GYN , etc .). ●
REFERENCE
1 . Hoffman M , Monroe DM 3rd . A cell-based model of hemostasis . Thromb Haemost . 2001 ; 85:958-65 .
4 Focus on Classical Hematology