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Heart 10 IV. HEART PHYSIOLOGY - How the heart beats. How the heart depolarizes the myocardium, which leads to a contraction. A) INTRINSIC CONTROL - Heart controls its own rhythm. HOW?

Depolarizations begin in the atria, spread down to the apex, where we begin contraction.

Why not put the pacemaker on the apex of the heart, if that is where we want contraction to begin? lag allows the ventricles to fill completely beforee we begin contracting them.

SYSTEM OF THE HEART (see image next page) Specialized muscle tissue wrapped up within connective tissues: speeds up current, and transmits a signal, acting like a nerve, although it is specialized

1 Heart 10 IV. HEART PHYSIOLOGY - How the heart beats. How the heart depolarizes the myocardium, which leads to a contraction. A) INTRINSIC CONTROL - Heart controls its own rhythm. HOW? The presence of gap junctions, and an area that is characterized by spontaneous depolarization. Therefore, heart beats as a single unit. Depolarizations begin in the atria, spread down to the apex, where we begin contraction. The veins and atria are superior of the ventricle, which allows the heart to use gravity to fill the ventricles (mostly; see later). The heart must pump upward, into the arteries. Why not put the pacemaker on the apex of the heart, if that is where we want contraction to begin? lag allows the ventricles to fill completely beforee we begin contracting them. This - We then have a seriess of specialized structures that carry the signal from the atria down to the apex, giving the heart the necessary time to fill the ventricles: THE INTRINSIC CONDUCTION SYSTEM OF THE HEART (see image next page) Specialized muscle tissue wrapped up within connective tissues: speeds up current, and transmits a signal, acting like a nerve, although it is specialized cardiac muscle and conducting fibers. Transmits the signal quickly and efficiently down to the apex. Steps of electric events of the myocardium: 1) AP initiated by autorhythmic cells at SINOATRIAL (SA) NODE - right atrium is specialized to generate APS 75x/ minute = fastest depolarization rate = the PACEMAKER. 2) From the SA node, the depolarizations move throughout the atria. The atria depolarize from top to bottom, followed by a slight contraction of the atria (rememberr their small amount of muscle, relative to the ventricles). This forces a little more blood down into the ventricles, thereby assuring their efficient filling (and therefor pumping, once they pump). Percentage filling gravity: 70-80% Percentage filling contraction of the atria: 20-30% However, the depolarizations are not passed directly to the ventricles, or else the ventricles would contract from top to bottom. There is a connective tissue wall between the atria and ventricles: the atrioventricular septum between the RA and LV, and the valves themselves. Connective tissues do not conduct depolarization s. 3) Now, the depolarizations are passed down to the superior portion of the interventricular septum, and the remaining parts of the Intrinsic Conduction System contained within: (i) ATRIOVENTRICULAR (AV) NODE A small nodee of muscle in the atrioventricular septum, which acts as a portal for depolarizations down to the interventricular septum. The small diameter of the node helps delay the signal, giving the atria time to contract. As it is only connectionn between the atria & ventricle, making sure we get current to the apex beforee spreading.

2 Heart 11 Image courtesy of National Heart, Lung, and Blood Institute (NHLBI) (ii) ATRIOVENTRICULAR BUNDLE (AV BUNDLE or BUNDLE OF HIS) - specialized bundle of conducting tissue that brings current to the apex before spreading to the rest of cardiac tissue. It splitss into the right & left BUNDLE BRANCHES. (iii) PURKINJE FIBERS - at the apex, bundles split upp finely, turn superiorly, exciting inferior ventricular cells. Then, depolarizations spreads up toward the atria. VENTRICLES CONTRACT FROM INFERIOR TO SUPERIOR!! - Having the SA node act as PACEMAKER and spread outward through these structures causes the heart to beat in a synchronized manner. Remember: both ventricles must pumpp at the same time!

Heart 12 B) EXTRINSIC CONTROL - MODIFICATION

Control Center is the cardioregulatory area

Taking information from baroreceptors to

Taking input from baroreceptors in Aortic

Fibers emerge from T1 - T5 of spinal cord,

ELECTROCARDIOGRAM - graphic recording of the

3 Heart 12 B) EXTRINSIC CONTROL - MODIFICATION of rhythm. - Nervous system can serve as either an accelerator or brake. Control Center is the cardioregulatory area in the medulla oblongataa that has both a cardioinhibitory region and a cardioacceleratory region. Taking information from baroreceptors to determine needs. Is pressure too high or too low? * PARASYMPATHETIC ACh decreases rate & force (CARDIOINHIBITORS). Innervates at the SA and AV nodes. Taking input from baroreceptors in Aortic Arch and Carotid Sinus. Increase pressure leads to increase parasympathetic output leads to decrease heart rate. * SYMPATHETIC - increase rate & force. Cardioacceleratory center of medulla activated. Fibers emerge from T1 - T5 of spinal cord, and innervate many places on the heart. This will increase rate (chronotropic effects) & strength of contraction (inotropic effects see later). C) ELECTROCARDIOGRAPHY (ECG or EKG) - ELECTROCARDIOGRAM - graphic recording of the electrical changes of f the heart. * put electrodes (LEADS) on body surface -----> look at changes at t different surface sites to get an idea of what is happening in the heart. * End up with TRACINGS: noteworthy INTERVALS: 3 waves of electrical flux (DEFLECTION WAVES), with some We will not be discussing all of them. You may have to know more than the ones discussed here.

4 Heart 13 Important point: Although contraction will follow these deflection waves a moment later, you are not looking at contraction directly. These deflection waves represent electrical flux through the myocardium ONLY! 1. P WAVE - depolarization of atria (starting at the SA node). ** 0.1 second later, atria contract. 2. QRS COMPLEX ventricular depolarization; drowns out atrial repolarization on the graph. Ventricular contraction happens a moment later. 3. T WAVE ventricular repolarization. ** PR INTERVAL The time allowed for ventricular filling. ** QT INTERVAL Beginning of ventricular depolarization until the end of ventricular contraction. This period is the entire event of ventricular contraction. * Changes in height of wave or distance between peaks = problems by disease or damage. - ARRHYTHMIAS - defect in the intrinsic conduction system causes irregular depolarizations, leading to uncoordinated atrial & ventricular contraction. **FIBRILLATION - rapid, out of phase contraction leading to bad pumping; eventually, circulation stops, leading to brain death. SHOCK THE HEART - interrupt the chaotic twitching by depolarizing the entire myocardium. Implantable cardioverter-defibrillator: A device implanted in the chest can electrically restart the heart iff it stops beating. Some devices can also stimulate thee heart to pump more effectively.

Heart 14 **HEART BLOCK - a blockage at any level of the electrical conduction system of the heart (shown

System. Severity depends on where it occurs. Other parts may take over, becoming the pacemaker.

functioning SA node of the humann heart.

bradycardia or ventricular fibrillation.

5 Heart 14 **HEART BLOCK - a blockage at any level of the electrical conduction system of the heart (shown in the diagram on the right) ) prohibits good conduction of the impulse through the Intrinsic Conduction System. Severity depends on where it occurs. Other parts may take over, becoming the pacemaker.. ECTOPIC FOCUS: an excitable group of cells that causes a premature heart beat outside the normally functioning SA node of the humann heart. Acute occurrence is usually non-life threatening, but chronicc occurrence can progress into tachycardia, bradycardia or ventricular fibrillation. One cause = tooo much smoking/caffeine; AV node generates AP faster than the SA node (both drugs excite the AV node). SA node: 75 beats/ /min AV node: 50 beats/ /min AV Bundle & Purkinje: 30 beats/ /min If the AV node takes over, heart rate = beats/min. Slow, but adequate. If ventricular impulses = too slow, putt in a FIXED RATE ARTIFICIAL PACEMAKER. Most modern pacemakers are DEMAND-TYPE PACEMAKER - delivers impulse onlyy when heart doesn t transmit own AP.

6 Heart 15 D) MECHANICAL EVENTS & CARDIAC CYCLE - CARDIACC CYCLE - all events associated with the flow of blood through heart. * SYSTOLE - contraction * DIASTOLE - relaxation - Traditionally, we describe events of left side of heart (SYSTEMIC CIRCUIT) which is the higher pressure circuit (it is what you measure when you measuree blood pressure at the arm). So assume we mean systemic ventricular systole if we simply say systole. However, both ventricles push at the same time, and the same volume, but, right side (pulmonary circuit) has a much lower blood pressure (~ 1/5 pressure of systemic circuit). - STEPS OF CARDIACC CYCLE: 1. VENTRICULAR FILLING - mid-late diastole (ventricle is ½ relaxed). * As the pressure in ventricle decreases, blood passes passively from atria through bicuspid into left ventricle (of course, same is happening on the right side of the heart). About 70% of blood comes in following gravity. * Atria contract, pushing remaining 30% of blood into ventricles and ventricles begin to depolarize. The amount of blood in the ventricles is called End Diastolic Volume. 2. VENTRICULAR SYSTOLE as atriaa relax, ventricles contract. This happens in 2 sub-phases that maximize the efficiency of pumping blood. AV valves close from backpressure as ventricles fill and begin to contract. Then: (a) ISOVOLUMETRIC CONTRACTION - Ventricles begin contracting, but without opening SL valves. Closed chambers means volume can t change ( isovolumetric ) ), but blood pressure greatly increases. (b) EJECTION PHASE - SL valves open, blood ejects out into arteries. 3. ISOVOLUMETRIC RELAXATION - early diastole. SL valves close due to backpressure from arteries. Relax the myocardium, but ventricles still completely closed off (same volume = isovolumetric ). This creates an extremely low pressure, helping to suck in during the next step VENTRICULAR FILLING TOTAL CARDIAC CYCLE TIME = 0.8 second (normal 70 beats/minute)

Heart 16 * NOTE: if it says isovolumetric, all the

* LASTLY, NOTE THIS: You can hear valves close, but not

and right after ventricular contraction; in other

valves close at the beginning and end of systole.

sounds. S2: SL Valves closing = sharper noise.

that in this module) * Abnormal heart sounds = HEART

Not always a bad sign, just thin walls, especially if

However, it may indicate valve problems.

valve does not close completely, causing the blood to

g.: Mitral insufficiency the mitral valve does not

It is the abnormal leaking of blood from the left

atrium, when the left ventricle contracts.

falls out of place (rectal, uterine, valve, etc.).

thickened mitral valve leaflet into the left atrium

7 Heart 16 * NOTE: if it says isovolumetric, all the valves are closed. * LASTLY, NOTE THIS: You can hear valves close, but not open. You are going to hear valves closing right before and right after ventricular contraction; in other words, heart sounds define the beginning and end of ventricular systole. E) HEART SOUNDS S1 & S2 ( lub-dub ) - Listening to the valves close at the beginning and end of systole. Indicates the QUIESCENT PERIOD (the pause is when the heart is not contracting). S1: AV closes = onset of systole = louder of the 2 sounds. S2: SL Valves closing = sharper noise. (There is often a third sound, but we won t be covering that in this module) * Abnormal heart sounds = HEART MURMUR. Blood strikes obstruction, becomes turbulent. Not always a bad sign, just thin walls, especially if heard in children. However, it may indicate valve problems. * 2 main categories of problems: Regurgitation - the valve does not close completely, causing the blood to flow backward instead of forward throughh the valve. E.g.: Mitral insufficiency the mitral valve does not close properly when the heart pumps out blood. It is the abnormal leaking of blood from the left ventricle, through the mitral valve, and into the left atrium, when the left ventricle contracts. Prolapse "to fall out of place" Any organ or structure falls out of place (rectal, uterine, valve, etc.). Mitral valve prolapse - Displacement of an abnormally thickened mitral valve leaflet into the left atrium during systole. There are various types of MVP, and not t all are dangerous. Stenosis - the valve opening is narrowed or does not form properly, inhibiting the ability of the heart to pump blood to the body due to the increased force required to pump blood through the stiff (stenotic) valve(s).

8 Heart 17 Analysis of the Wiggers Diagram: This will not be on the exam, but it is a good check to see if you get it!

THE CARDIOVASCULAR SYSTEM. Heart 2

THE CARDIOVASCULAR SYSTEM. Heart 2 THE CARDIOVASCULAR SYSTEM Heart 2 PROPERTIES OF CARDIAC MUSCLE Cardiac muscle Striated Short Wide Branched Interconnected Skeletal muscle Striated Long Narrow Cylindrical PROPERTIES OF CARDIAC MUSCLE Intercalated