Excitability ability to respond to an electrical impulse Conductivity ability

Excitability ability to respond to an electrical

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Excitability – ability to respond to an electrical impulse Conductivity – ability to transmit an electrical impulse Contractility – ability to contract after receiving a stimulus Automaticity – ability to initiate an electrical impulse (specialized cells e.g. SA node and Purkinje fibers) SA Node rate (Primary pacemaker): 60 - 100 bpm AV Node rate: 40 - 60 bpm Ventricle rate: 15 - 40 bpm **Electrical Impulse Precedes Mechanical Contraction Bradycardias -HR is too slow Low cardiac output: SA node not firing correctly; Abnormal conduction between the atria and ventricle S/S: fatigue, dizziness, fainting Tachycardias -HR is too fast Not enough diastolic time for filling of ventricles Ventricular tachycardia/fibrillation : MOST DANGEROUS! Ventricles contract before filling with blood Ventricles quiver instead of beat. Therefore, the heart can’t pump blood to the body! -Electrical conduction begins in the ventricles! S/S: Dizziness, lightheadedness, cardiac arrest! KNOW: Cardiac output can be compromised in either situation. Severity depends on The rhythm, comorbidities. *Goal of treatment in any arrhythmia is to maintain or restore cardiac output. Remember, without adequate cardiac output, the rest of the body is not getting enough blood, so organs are not getting enough oxygen! Atrial Fibrillation (A-Fib)
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*Pumping action of atria and ventricles dyssynchronous: “fibbing” of the atria **Blood doesn’t move out rapidly enough and causes stasis of blood in the atria (blood thickens and clots) Types: Chronic; Acute with Rapid Ventricular Rate (HR > 150) Consequences: Chronic: Blood pools in the atria = blood clots = travel (could travel to brain and cause stroke) Rapid ventricular rate: HR too fast = decreased CO; Fatigue, SOA, syncope (fainting) Treatment: Immediate: Cardioversion (give heart a shock; SA takes back over) or IV gtt Long term maintenance: Anticoagulants; Medications to control HR (goal < 110 bpm) Endocardial and Pericardial Infective Endocarditis Invasion of valves and endocardium by microbial agent (majority bacteria) -Vegetation, destruction of cardiac tissue Portal of entry: dental or surgical procedure most common -High risk: structural abnormalities of the heart valves, congenital heart disease Acute manifestations: High fever and chills Cause: Staph infection Treatment: treat the cause (antibiotics) Rheumatic Fever/Rheumatic Heart Disease Immune-mediated, multisystem inflammatory disease (involving heart, skin, and connective tissue) - Weeks after Group A Strep pharyngitis in children and young adults -Bacteria initiates immune response Acute RHD: inflammation all 3 layers of the heart -Chronic deformity and impairment of a valve(s) can be consequence -Aortic and mitral most common Cardiac manifestations: mitral valve regurgitation, heart failure, new onset heart murmur, arrhythmias Treat: antibiotics, anti-inflammatories Acute Pericarditis Pericardial inflammation lasting less than 2 weeks: Inflammatory response Causes: viral (majority ), bacterial (Rheumatic fever), connective tissue diseases, post-MI, post cardiac surgery, neoplasms
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