The Heart: Structure and Function in a Clinical Scenario PDF

THE HEART Structure and function in a clinical scenario DRS. HATFIELD, MACHART, AND WALLACE JEREMIAH WILSON: SYMPTOM ONSET Jeremiah Wilson, a 65-year-old male, is tending to his garden when he suddenly develops chest tightness and left shoulder pain. He calls 9-1-1 and is transported to your hospi...

THE HEART Structure and function in a clinical scenario DRS. HATFIELD, MACHART, AND WALLACE JEREMIAH WILSON: SYMPTOM ONSET Jeremiah Wilson, a 65-year-old male, is tending to his garden when he suddenly develops chest tightness and left shoulder pain. He calls 9-1-1 and is transported to your hospital. JEREMIAH WILSON’S VITALS Upon arrival at the Emergency Department, his vitals are taken: BP: 90/52 mmHg < Which of these are abnormal? All! Temperature: 98.9° F (37.2° C) RR: 33 breaths per minute, labored SaO2: 89% HR: 120 bpm irregular  JEREMIAH WILSON’S DIAGNOSIS You make the call that this is a heart attack. Based on presentation (chest tightness and left shoulder pain) and vitals, why this diagnosis? BP: 90/52 mmHg low 120/80 Temperature: 98.9° F (37.2° C) 98.6oF, 37oC RR: 33 breaths per minute, labored 12-20 breaths/min SaO2: 89% 95-100% HR: 120 bpm irregular 60-90 bpm THE MEDIASTINUM, HEART, AND GREAT VESSELS RV Pericardium fixed to central tendon of the diaphragm THE HEART IS SURROUNDED BY FIBROUS AND SEROUS PERICARDIUM Fibrous pericardium Serous pericardium parietal visceral HOW ARE YOU GOING TO FIND THE BLOCK? You need to visualize Jeremiah’s coronary arteries using a cardiac catheter. ANATOMY OF CIRCULATION Trace flow of blood in CV system, starting with RA Systemic circulation – Coronary circulation Pulmonary circulation CORONARY ARTERIES Right coronary Left Coronary Circumflex Nodal (not shown) Anterior interventricular/left anterior descending (LAD) Marginal Posterior interventricular/Posterior descending (PDA) HOW CORONARY ARTERIES GET FILLED SEMILUNAR VALVES – AORTIC AND PULMONIC aortic pulmonic Aortic Valve Ascending aorta Coronary artery opening Nodule Valve cusp Aortic sinus of Valsalva Left Ventricle USE YOUR KNOWLEDGE OF BLOOD CIRCULATION TO EXPLAIN THE FOLLOWING: Plaque in coronary arteries  Myocardial infarction (MI) Embolism in left atrium  Stroke Deep vein thrombosis (DVT)  Pulmonary embolism (PE) PHYSIOLOGY OF FLOW Learning Objectives: Relate Ohm’s (Darcy’s) law of flow to the cardiovascular system. Understand the parameters of pressure and resistance. Understand the concept that flow remains approximately constant in a closed loop system. Quantify the inverse relationship between total cross-sectional area and velocity of flow. Determine the effect of reduced radius on flow and velocity of flow. Apply these concepts to pathologies.  First Equation for flow: Ohm’s law of flow Aka Darcy’s Law of Flow Flow (Q)  P/R Note: Mean or average flow! LO: Relate Ohm’s (Darcy’s) law of flow to the cardiovascular system Silverthorn Fig 15.1 LO: Understand the concept that flow remains approximately constant in a closed loop system The Arterial Tree  As fluid moves through a closed system of pipes... Flow rate stays constant Velocity of flow decreases LO: Understand the concept that flow remains approximately constant in a closed loop system  Second equation for flow: Q = velocity * x.s. area LO: Quantify the inverse relationship between total cross-sectional area and flow Silverthorn Fig 15.17 Back to Darcy’s law: Flow  P/R What generates the pressure gradient? LO: Understand the parameters of pressure and resistance. Silverthorn Fig. 15.6  Elastic recoil becomes the driving Heart contraction creates pressure force for the flow during diastole ventricular ventricular contraction relaxation ↓ ↓ systole diastole (systolic) (diastolic) pressure Arteries are a __________ reservoir. Figure 15.5 (Human Physiology, Silverthorn, 8e) Silverthorn Fig. 15.6  What generates the resistance? Resistance to flow = the friction that opposes flow Resistance to fluid flow in a cylinder Poiseuille’s (pwa zhwa) Law): R = 8L/r4 Which factor plays greatest role in determining resistance? LO: Understand the parameters of pressure and resistance.  P1 Pressure drop P2 Hemodynamics ΔP F = flow (Ohm’s Law or F= F∝ P = pressure (P1-P2) R = resistance R R = resistance to flow Darcy’s Law) to flow R = resistance to flow η = viscosity r 8ηl η = (eta) viscosity R= of blood R= Poiseuille’s Law 𝛱 r4 l = length r = radius l ΔP P1 Pressure drop P2 Q= flow (L/s) Flow r P = pressure (P1-P2) F∝ F ∝ ΔP r4 η = (eta) viscosity constant! η = viscosity of blood l = length constant! r = radius l  Re: Q = velocity x area When a vessel constricts, does velocity of flow increase in order to keep flow constant? LO: Determine the effect of reduced radius on flow and velocity of flow. LO: Determine the effect of reduced radius on flow and velocity of flow. Silverthorn Fig 15.13  Relate to Jeremiah Wilson’s condition LO: Apply these concepts to pathologies. Key Points: The behavior of blood in the cardiovascular (CV) system can be explained by the principles of fluid flow, such as Darcy’s law: Q = ΔP/R Resistance to flow is largely due to effect of radius, which is rapidly regulated, while length and viscosity remain ~ constant. The CV system is a closed loop so therefore flow rate is ~ maintained, especially from aorta to capillaries. Velocity of flow decreases as blood moves into greater total cross-sectional area. V = Q/A. The decrease in velocity is due to less pressure per particle as the particles spread apart; lower velocity allows time for exchange. If a vessel is constricted, flow rate in the vessel decreases. We cannot assume that velocity increases in order to maintain flow rate! Pathologies such as stenosis or atherosclerosis reduce flow to whatever is downstream! JEREMIAH WILSON’S DIAGNOSIS, CONT. Cardiac catherization reveals that Jeremiah’s left coronary artery is 100% occluded. He will need a stent placed immediately. What heart structures are at risk with an occluded LCA? COLOR THE SUPPLY FIELD OF THE LEFT LCA Anterior Posterior Figures from Medscape ARTERIAL SUPPLY TERRITORIES Anterior view Posterior view  CORONARY ARTERIAL DOMINANCE – WHICH ARTERY GIVES RISE TO POSTERIOR DESCENDING ARTERY (PDA) AND SUPPLIES INFERIOR THIRD OF INTERVENTRICULAR SEPTUM ~70-80% of population is right dominant ~10-15% left dominant ~20% codominant Right dominant Left dominant Codominant IS THIS HEART RIGHT OR LEFT DOMINANT? IS THIS HEART RIGHT OR LEFT DOMINANT? THE RCA USUALLY SUPPLIES THE NODES 40% of people, SA node supplied by LCA (nodal artery from circumflex branch) 20% of people, AV node supplied by LCA branch SINOATRIAL NODAL ARTERY VARIATION Vikse et al. (2016). Anatomical Variations in the Sinoatrial Nodal Artery: A Meta-Analysis and Clinical Considerations. PloS one. 11. e0148331. 10.1371/journal.pone.0148331. THE INTERVENTRICULAR SEPTUM AND THE AV BUNDLE BRANCHES ARE PRIMARILY SUPPLIED BY LAD LABEL INTERNAL ANATOMY OF LEFT VENTRICLE Trabeculae carneae Interventricular septum Mitral valve Chordae tendineae Papillary muscles Aortic valve and cusps NO OTHER BLOCKAGES IDENTIFIED; CABG NOT NEEDED Coronary artery bypass graft (CABG) carried out in more complex coronary artery disease cases Coronary artery disease is buildup of plaque in walls of coronary 4 arteries, causing narrowing or 3 blockage that could lead to heart 2 1 attack Sites 1, 2, and 3 (right figure) account for at least 85% of all occlusions  CORONARY ARTERY BYPASS GRAFT Vessels used include: LIMA or RIMA Radial artery Great saphenous vein JEREMIAH WILSON UNDERGOES AN EKG Results indicate STEMI, or S-T Elevation Myocardial Infarction What does this mean? HEART CONDUCTION PHYSIOLOGY Learning Objectives: Describe the electrical activity of pacemaker versus contractile cells. Discuss autonomic regulation of heart rate. Relate the electrical activity of heart cells to the electrocardiogram (ECG). Predict the effect of pathologies on the ECG. Silverthorn Fig 14.9 Silverthorn Fig 14.15 If channel threshold Silverthorn Fig. 14.13 52 Autonomic regulation Silverthorn Fig. 14.20a ELECTROCARDIOGRAPHY (ECG OR EKG) Wave of depolarization in cardiac cells Body fluids act as a conductor; causes currents to flow in ECF ECG records potential changes at skin surface Bipolar leads have a positive and a negative electrode placed on skin Note: repolarization wave is opposite Where is the signal during the PR segment? Poll SA node—before P wave Internodal pathways—before or at beginning of P wave Atria—P wave AV node—PR segment = AV node delay Ventricles—R wave How does the ECG relate to pacemaker and contractile APs? Where does the ventricular Ca2+ plateau correspond to the ECG? Poll P wave PR segment R wave ST segment T wave COMPARE AND CONTRAST ECGS  Heart Block: An Electrical Pathology Predict: If conduction through AV node is completely blocked... the PR segment will be > 200 msec in duration—partial or 1st degree heart block cardiac output will be reduced to zero—ventricular fibrillation the P and QRST will be completely dissociated the heart will fibrillate What is fibrillation? Ischemia ECG STEMI ECG Progression Key Points Pacemaker cells have “funny channels” that open each time Vm returns to – 60 mV, giving rise to spontaneous and rhythmic beat of heart. Pacemakers also have Ca2+ action potentials (APs). Contractile cell APs have calcium plateau that prolongs the depolarization, preventing tetany and allowing for ventricular filling. As the heart cells depolarize and repolarize, currents flow in the ECF, creating small potential differences (p.d.s) at surface of skin. These p.d.s are picked up and amplified by electrodes placed on the skin, in a process known as electrocardiography. The recording is known as an electrocardiogram or ECG. Normal ECG complexes show atrial depol (P wave), ventricular depol (R wave), and ventricular repol (T wave). A depolarization spreading toward a positive pole will produce a positive (upward deflected) wave. …negative pole negative wave. Repol is opposite! Pathologies: Partial heart block lengthens PR segment/interval. Complete heart block results in dissociated P and QRST complexes. Fibrillation is uncoordinated depolarization and contraction. Elevated ST segment is characteristic of myocardial infarction. AFTER STENT PROCEDURE, JEREMIAH IS PUT ON BLOOD THINNERS...