Cardiology: Back to Basics

This segment is brought to you via guest contributor, Jayson McConnell. 

AN EYE-OPENING EDUCATION

It was a quiet May afternoon working in an a high-volume EMS service. As I was finishing one chart, the tones drop yet again. “Medic 13, we have a priority one run for you on chest pain and shortness of breath.” Just like every other run in my career, I responded to the call without hesitation. Our unit arrived on scene with the local fire department and the patient who had made his way out to the end of the driveway. As I approached the patient, I introduced myself and my partner and I started our assessment. The patient was awake, alert, and oriented. He appeared to be in good health. His skin was pink, warm, and dry. The patient had no problem speaking in long winded sentences and did not have any signs of shortness of breath or difficulty breathing for that mater. I questioned the patient about his chest pain and any other related symptoms. At this time the patient was essentially pain free and looked be back to his normal pre-incident status. The local fire department was dismissed and the patient was assisted to the ambulance for further assessment and in my mind, a possible refusal of transport. At this time the patient was laughing and joking with us, “I think it’s just stress or it’s my way out of my honey do list for the day”. After a brief interview and with some additional encouragement the patient agreed to allow me to apply the heart monitor and check some baseline vitals. The patient’s vital signs were nearly the same as a world class athlete: BP 118/68, RR 12, lung sounds clear and equal bilaterally both anterior and posterior auscultation.  The monitor display showed a heart rate of 68 normal sinus and the 12-lead revealed a left bundle branch block (LBBB) with some slight ST-segment abnormalities.

sgarbossa1

I began to explore his medical history and any possible contributing factors. The patient denied any medical history, didn’t take any prescribed medications, and had no family or lifestyle risk factors for acute coronary syndrome (ACS). At this point, I was running out of ideas. I asked the patient to repeat his story one more time to make sure I had everything correct before allowing him to sign a refusal form. During the third and final question and answer session, the patient decided to mention the near syncope incident that preceded this entire episode. “Oh, I didn’t hear you mention the feeling of almost passing out” I said. With the near syncope, chest pain, and acute shortness of breath, the patient finally agreed to be treated and transported to the hospital. We ran through the standard treatment: aspirin, nitro, and oxygen. The patient continued to be pain free with no other symptoms present through transport. A repeat 12-lead was done en route, strictly due to my own curiosity. LBBB was noted with no additional changes from the first. “I told you, it’s just the stress.” said the patient. As we continued to joke back and forth, the patient appeared to be back to his normal. I told this patient its probably nothing serious. “I don’t believe you are having a heart attack from the 12-leads we have performed.” Pairing my assessment with the patients nonexistence for previous medical history, I truly believed this would be a simple in-and-out for the patient. We pulled in to the hospital and transferred the patient  to the ER cot with a bedside report to the receiving RN and attending ER physician. The ED staff started with all of the normal treatments: lab draws, monitor applied, and a 12-lead.

As I finished up with my signatures and shaking the hand of my patient, the ER physician requested a copy of my 12-leads for comparison. Crap. Did I miss something obvious? Returning to the ER with 12-leads in hand, I began to converse with the physician again. He interrupted our conversation to contact the cath lab and activate the system for emergent cath procedure. As the Physician hung up the phone, I hoped and prayed he would not walk into my patients room and tell him the bad news. I could feel the anxiety set in followed by the palpitations and nausea. The physician returned to the patient’s room with the news, “Sir, you’re having a heart attack”. I hung my head low and departed the emergency room and returned to the ambulance where my paramedic partner was restocking the ambulance. “What’s wrong with you?” he asked. “I somehow just missed a MI on that guy” I replied. A few minutes of silence went by and just as the nausea was letting up, someone tapped me on my shoulder. I turn around to see the ER physician. “Do you know why you missed that one” asked the physician. Before I could produce any response the physician said “it’s because you were never taught to look for those kinds of heart attacks”. The look of confusion and anger must have been plastered all over my face because just moments later the physician smiled, laughed, and said “Follow me, I’ll explain it to the both of you”.

After a brief field education and a new term I had never heard before, I returned to my ambulance more determined than ever.  Sgarbossa? WTF, I thought to myself.  As I look back, I can now answer that questions that I must have asked myself over a hundred times that day.  What just happened was that I had received an incredible education that I didn’t know I needed.  Along with that education, the physician ignited the desire for me to learn cardiology.  Over the next few years I would dive deep into cardiology books, attend multiple cardiology in-services, interview local cardiologists, and download, print, and review any online documents I could find.  What I discovered is that the subject of cardiology is much more complex than what was presented to me in paramedic class.  The purpose of this blog, and the next few blogs that follow, is to explain and expand on some of the information and education I have been able to gather over the past few years.  I want to provide the hard to find and even harder to interpret information along with some addition education of cardiology topics to you the reader.  The plan for this series of blogs is to start at the beginning with heart anatomy including the electrical pathways and the coronary arteries and progress all the way through each type of myocardial infarction (MI) and anything in between.  Along with the breakdown of each category of MI, case studies, actual 12-leads, and video imaging will be presented to help explain the topics from multiple angles.

Back to the Basics

Heart Anatomy

The heart is made up of four chambers, with each chamber completing a specific task each time the heart contracts.  The right side of the heart operates on a low pressure scale and contains the right atrium and right ventricle.  The primary function of the right side of the heart is to receive blood from the body and pump it to the lungs for oxygen and carbon dioxide exchange.  The left side of the heart operates on a high pressure scale and contains the right atrium and right ventricle.  The primary function of the left side of the heart is to receive oxygenated blood from the lungs and pump it throughout the body.

Right Side of the heart

Blood enters the heart through two large veins, the inferior and superior vena cava, emptying oxygen-poor blood from the body into the right atrium. As the atrium contracts, blood flows from your right atrium into your right ventricle through the open tricuspid valve. When the ventricle is full, the tricuspid valve shuts. This prevents blood from flowing backward into the right atrium while the ventricle contracts. As the ventricle contracts, blood leaves the heart through the pulmonic valve, into the pulmonary artery and to the lungs, where it is oxygenated. The oxygenated blood then returns to the heart through the pulmonary veins.

Left Side of the Heart

The pulmonary veins empty oxygen-rich blood fromheart the lungs into the left atrium.  As the atrium contracts, blood flows from your left atrium into your left ventricle through the open mitral valve.  When the ventricle is full, the mitral valve shuts. This prevents blood from flowing backward into the atrium while the ventricle contracts.  As the ventricle contracts, blood leaves the heart through the aortic valve, into the aorta and to the body.  During relaxation, blood flows into the right coronary artery (RCA) and left coronary artery (LCA) to provide blood flow to the heart.

Tracing the Hearts Electrical Pathways

The contraction of the muscle fibers in the heart is very organized and pathwayscontrolled. Rhythmic electrical impulses flow through the heart in a precise manner along distinct pathways and at a controlled speed. The sinoatrial node (1) initiates an electrical impulse that flows through the right and left atria (2), making them contract. When the electrical impulse reaches the atrioventricular node (3), it is delayed slightly. The impulse then travels down the bundle of His (4), which divides into the right bundle branch for the right ventricle (5) and the left bundle branch for the left ventricle (5). The impulse then spreads through the ventricles, making them contract.

The rate at which the pacemaker sends out its impulses, and thus governs the heart rate, is determined by two opposing systems—one to speed the heart rate up (the sympathetic division of the nervous system) and one to slow it down (the parasympathetic division). The sympathetic division works through a network of nerves called the sympathetic plexus and through the hormones epinephrine(adrenaline) and norepinephrine (noradrenaline), which are released by the adrenal glands and the nerve endings. The parasympathetic division works through a single nerve—the vagus nerve—which releases the neurotransmitter acetylcholine.

Coronary Artery Anatomy

Coronary arteries supply blood to the heart muscle and like all other tissues in the body, the heart muscle needs oxygen-rich blood to function.  The coronary arteries consist of two main arteries: the RCA and LCA.  The left coronary artery then splits into two additional main branches: the left anterior descending (LAD) and the circumflex artery (Cx).  To try and simplify the coronary anatomy lets isolate each artery and take an in-depth look.  For this blog we are going to assume normal cardiac anatomy and leave out any of the abnormal cardiac anatomy presentations.

Right Coronary Artery

The right coronary artery emerges from the aorta just a short distance from the heart.  The artery travels in the AV grove giving way to multiple branches until turning posteriorly to supply blood flow to the back side of the heart.  For purposes of simplicity this blog will focus on RCA and the two main branches:  the right marginal branch and the posterior descending artery.  Near the start of the RCA a small artery knows as the sinoatrial nodal artery to supply blood flow to the SA node.  Studies very slightly, but this appears true for approximatly 60% of the population.  In the remaining 40% the sinoatrial nodal branch comes from the LCA.   Continuing down the RCA the right marginal branches off and travels toward the apex and continues to supply blood flow to the right ventriclerca1 and inferior portion of the right and left ventricles.  Next the posterior descending artery wraps around to the back of the heart just after the marginal branch to provide blood supply to the posterior wall of the right ventricle and the posterior and inferior portion of the left ventricle along with the posterior septum wall.  This artery and its main branches will be shown in more detail in a following blog along with video imaging.

Left Coronary Artery

The left coronary artery is tasked with providing blood flow to a slightly larger area.  The left coronary artery emerges from the aorta, and passes between the pulmonary trunk and the left atrial appendage. Under the appendage, the artery divides into the anterior interventricular descending artery (LAD) and the left circumflex arteryreaper-heart-5-300x295-jpg1(LCx).  This division happens fairly anterior and results in a very small LCA compared to the RCA.  The short length of the LCA is actually beneficial in some ways because there is less room for occlusions to happen  resulting in the well known field term “the widow maker”.  The branches of the LCA are more complexed and will require some detailed explanations in an attempt to paint a clear picture.  The first branch of the left coronary artery is the LAD and it travels along the anterior portion of the heart through the anterior interventricular sulcus (AIVS), an anterior groove in between the right and left ventricles and toward the apex.  The branches off the LAD include: the diagonal artery branches and septal artery branches.  The diagonal branches course diagonally on the anterolateral portion of the left ventricle and provide blood flow to large portions of the anterior wall. The first diagonal branch is designated as D1; the second diagonal branch is designated as D2; and so on.  Again for simplicity the focus will be D1 and D2 only.  For anatomy purposes the portion of the LAD between D1 and the LCA split is refereed to as the proximal LAD.  The last 1/3 of the LAD is refereed to as the distal LAD.  The portion of the LAD that is between the proximal and distal LAD is refered to as?  Yep you guessed it, the mid-LAD.  As the LAD courses through the anterior interventricular sulcus it gives off several branches called septal perforators (SP), which supply blood to the interventricular septum.

The left circumflex artery(LCx) originates at the bifurcation of the LCA and passes down the left atrioventricular groove. The LCx branches into smaller branches called Obtuse marginal (OM) as it paslca1ses down the groove. It also gives rise to one or two left atrial circumflex branches that supply the lateral and posterior aspects of left atrium.  Finally the artery wraps around the lateral wall and travels down the posterior interventricular groove giving the posterior descending artery blood supply.

Wrapping it Up

Its obvious that there is a lot of information thrown at you in this blog. For most paramedics, this is probably just review, but we felt this was a great place to start.  The section on coronary arteries was a bit lengthy and detailed and it was planned that way.  To truly understand some of the cardiology topics and myocardial infarcts in the future blogs, a solid understanding of this anatomy will be crucial. We hope this blog was helpful, enjoyable, and beneficial for you, and we hope you stay tuned for our next cardiology blog on STEMI imitators.  As always, comments, questions, and academic feedback are welcome!

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