Plan of the lecture

1. Organization of the circulatory system.

2. Cardiac cycle.

3. Conductive system of the heart.

4. Mechanisms of compensation

5. Arhytmias of the heart. Deffinition. Classification. Pathogenesis.

6. Ischaemic heart disease.

6. Heart failure.

Actuality of the lectureActuality of the lectureThe disorders of cardiac rhythm concern to complex manifestations of

pathology of heart. Its can arise in rather small damage of the conducting system, and in some cases in structural changes. More often arrythmia arise with infectious illnesses and intoxications as consequence of miocarditis or dystrophy processes in cardiac muscle, and also in heart ishemic disease, cardiosclerosis.

The disorders of cardiac rhythm arise also owing to reflex influences from various interreceptors areas (disease of liver, intestinal tract, uterus), and also in hemodynamic disorders (arterial hypertension). Not infrequently аrrythmia is a result of disturbance of functions central and vegetative parts of nervous system. For example, the increase of activity parasymphatic nervous system lead to delay of conductivity. Similar is observed also by overdose of some medicin drugs (digitalis, quinidine, morphine). If bradycardia is accompanied complete atrioventricular blockade, can occur ischemia of brain with loss consciousness and occuring spasmes.

Arrythmia can be result in development of cardiac insufficiency.

FUNCTIONAL ORGANIZATIONOF THE CIRCULATORY SYSTEM

■ The circulatory system consists of the heartheart, which pumps blood; the arterial systemarterial system, which distributes oxygenated blood to the tissues; the venous systemvenous system, which collects deoxygenated blood from the tissues and returns it to the heart; and the capillariescapillaries, where exchange of gases, nutrients, and wastes occurs.

■ The circulatory system is divided into two parts: the low-pressure pulmonary low-pressure pulmonary circulationcirculation, linking the transport function of the circulation with the gas exchange function of the lungs; and the high-pressure high-pressure systemic circulationsystemic circulation, providing oxygen and nutrients to the tissues.

■ The circulation is a closed system, so the output of the right and left heart must be equal over time for effective functioning of the circulation.

THE THE HEARTHEART■ ■ The The heart is a four-chamberedheart is a four-chambered pump pump

consisting of consisting of two atriatwo atria (the right atrium, (the right atrium, which receives blood returning to the which receives blood returning to the heart from the systemic circulation, and heart from the systemic circulation, and the left atrium, which receives the left atrium, which receives oxygenated blood from the lungs) and oxygenated blood from the lungs) and two ventriclestwo ventricles (a right ventricle, which (a right ventricle, which pumps blood to the lungs, and a left pumps blood to the lungs, and a left ventricle, which pumps blood into the ventricle, which pumps blood into the systemic circulation).systemic circulation).

■ ■ Heart valvesHeart valves control the direction of control the direction of blood flow from the atria to the ventricles blood flow from the atria to the ventricles (the (the atrioventricular valvesatrioventricular valves), from the ), from the right side of the heart to the lungs right side of the heart to the lungs ((pulmonic valvepulmonic valve), and from the left side of ), and from the left side of the heart to the systemic circulation the heart to the systemic circulation ((aortic valveaortic valve).).

■ ■ The The cardiac cyclecardiac cycle is divided into two is divided into two major periods: major periods: systolsystole, when the e, when the ventricles are contracting, and ventricles are contracting, and diastolediastole, , when the ventricles are relaxed and when the ventricles are relaxed and filling.filling.

■ ■ The The work and efficiency of the heartwork and efficiency of the heart is determined by the volume of blood it is determined by the volume of blood it pumps out (pumps out (preloadpreload), the pressure that it ), the pressure that it must generate to pump the blood out of must generate to pump the blood out of the heart (the heart (afterloadafterload), and the rate at ), and the rate at which it performs these functions (which it performs these functions (heart heart raterate).).

Electrocardiogram (ECG)Electrocardiogram (ECG)

(Frank-) Starling Law(Frank-) Starling Law

• Within limits, the greater the stretching of the muscle fibers (preloadpreload), the greater the force of contraction.

• The extra force of contraction is necessary to pump the increased volume of blood from the ventricle.

• Cardiac output increases

Neural reflexesNeural reflexes• Bainbridge reflex – increased heart rate due

to increased right atrial pressure• Increased pressure in arteries stimulates a

baroreceptor reflex that decreases heart rate.

Cardiac Conduction Cardiac Conduction SystemSystem

Origin and Spread Origin and Spread of Excitation in the of Excitation in the

HeartHeart

c

ARRHYTHMIAS OF HEARTARRHYTHMIAS OF HEART Violation of rhythm of heart Violation of rhythm of heart accompanies a accompanies a

number of diseases of the cardio-vascular system. number of diseases of the cardio-vascular system. Most often they are observed at coronary Most often they are observed at coronary insufficiency. insufficiency. Arrhythmia registered Arrhythmia registered in in the acute the acute period of heart attack of myocardium in 95-100 % period of heart attack of myocardium in 95-100 % patientspatients..

In most world countries In most world countries sudden cardiac death is sudden cardiac death is about 15 %about 15 % from all cases of «natural» death. The from all cases of «natural» death. The main reason of sudden death at cardiac pathology main reason of sudden death at cardiac pathology in 93 % is arrhythmias. in 93 % is arrhythmias.

Arrhytmias are violation of frequency, rhythm, Arrhytmias are violation of frequency, rhythm, co-ordination and sequence of heartbeatco-ordination and sequence of heartbeat..

Etiology of heart rhythm disorderEtiology of heart rhythm disorderThe rhythm violations arise under the influence of different The rhythm violations arise under the influence of different

pathological agents, which can be divided on such groups:pathological agents, which can be divided on such groups: Functional violationsFunctional violations and and influencesinfluences, for example: , for example:

violation of vegetative nerves systemviolation of vegetative nerves system condition (sympathetic condition (sympathetic or parasympathetic link hyperactivity), or parasympathetic link hyperactivity), physical workphysical work, , physical physical overloadoverload, , body temperature changesbody temperature changes, , the increase of the increase of intracranium pressureintracranium pressure, , respirationrespiration (especially in children); (especially in children);

Organic injury of myocardiumOrganic injury of myocardium, for example: , for example: inflammation inflammation of myocardiumof myocardium (as the result of infection), the (as the result of infection), the myocardium myocardium dystrophydystrophy (in the result of hypoxia, ischemia or amiloidosis), (in the result of hypoxia, ischemia or amiloidosis), necrosis of myocardiumnecrosis of myocardium;;

Influences of toxic substances on the myocardiumInfluences of toxic substances on the myocardium (alcohol, drugs, big dose adrenalin and noradrenalin, (alcohol, drugs, big dose adrenalin and noradrenalin, glucocorticoids, bacterial toxins, phosphororganic glucocorticoids, bacterial toxins, phosphororganic substances);substances);

Hormone balance disorderHormone balance disorder (hyperthyroidism, (hyperthyroidism, hypothyroidism, hyperfunction of supranephral glands);hypothyroidism, hyperfunction of supranephral glands);

Violation of intracellular or extracellular ions balanceViolation of intracellular or extracellular ions balance (changes of sodium, potassium, calcium, magnesium and (changes of sodium, potassium, calcium, magnesium and chlorine concentration);chlorine concentration);

Mechanical influences on the heartMechanical influences on the heart (catheter using for the (catheter using for the diagnosis and treatment heart diseases, operation on the diagnosis and treatment heart diseases, operation on the heart, chest trauma).heart, chest trauma).

• Development of arrhythmias Development of arrhythmias can be related to can be related to violations of basic functions of the conducting violations of basic functions of the conducting system of heart: system of heart:

1) automatism1) automatism, , 2) 2) excitability excitability and and 3) 3) conductivity. conductivity.

• Classification of arrhythmias:Classification of arrhythmias:I. Arrhythmias, related with violations of automatism.I. Arrhythmias, related with violations of automatism.II. Arrhythmias, related with violations of excitability.II. Arrhythmias, related with violations of excitability.III. Arrhythmias, related with violations of III. Arrhythmias, related with violations of

conductivity.conductivity.IV. Arrhythmias, related with violations of excitability IV. Arrhythmias, related with violations of excitability

and conductivity.and conductivity.

Normal Rhythms

Arrhythmias, related with Arrhythmias, related with violation ofviolation of automatism automatism of of

heartheart Distinguish two groups of arrhythmiasDistinguish two groups of arrhythmias, related with , related with

violation violation of automatism of heart.of automatism of heart.1) 1) Nomotopic arrhythmiasNomotopic arrhythmias - - the generation of impulsesthe generation of impulses, as , as

well as in a norm, well as in a norm, takes place by takes place by pacemaker cells (P-pacemaker cells (P-cells) in cells) in sinoatrial [sinus] node, [nodus sinuatrialis]sinoatrial [sinus] node, [nodus sinuatrialis]. To . To them belong:them belong:

a) a) sinus tachycardiasinus tachycardia is multiplying frequency of cardiac is multiplying frequency of cardiac reductions;reductions;

b) b) sinus bradycardiasinus bradycardia is diminishing of frequency of is diminishing of frequency of cardiac reductions;cardiac reductions;

c) c) sinus (respiratory) arrhythmiasinus (respiratory) arrhythmia is a change of frequency is a change of frequency of heartbeat in the different phases of respiratory cycle of heartbeat in the different phases of respiratory cycle (become more frequent at inhalation [breath] and (become more frequent at inhalation [breath] and diminishing is at exhalation [outward breath]).diminishing is at exhalation [outward breath]).

Arrhythmias, related with Arrhythmias, related with violation of automatismviolation of automatism

Heterotopic ArrhythmiasHeterotopic Arrhythmias2) 2) heterotopic arrhythmiasheterotopic arrhythmias are are a syndrome of a syndrome of weakness of sinus weakness of sinus

nodenode.. The generation of impulses appears into other structures of The generation of impulses appears into other structures of the conducting system. A syndrome develops as a result of the conducting system. A syndrome develops as a result of diminishing of activity or stopping of activity of sinus node at the diminishing of activity or stopping of activity of sinus node at the damage of it cells or primary functional violations. The followings damage of it cells or primary functional violations. The followings types of pathological rhythms of heart can develop:types of pathological rhythms of heart can develop:

a) a) atrium slow rhythmatrium slow rhythm - a driver of rhythm is in the structures of - a driver of rhythm is in the structures of left atrium, frequency of heartbeat left atrium, frequency of heartbeat lesser than 70 per 1 minlesser than 70 per 1 min;;

b) b) atrio-ventricular rhythmatrio-ventricular rhythm - the source of impulses are drivers - the source of impulses are drivers of rhythm of the II order (overhead, middle or lower part of atrio-of rhythm of the II order (overhead, middle or lower part of atrio-ventricular node), frequency of heartbeat in dependence on the ventricular node), frequency of heartbeat in dependence on the place of generation of impulses place of generation of impulses diminishes from 70 to 40 per diminishes from 70 to 40 per minuteminute ; ;

c) c) idioventricular rhythmidioventricular rhythm - the generation of impulses appears in - the generation of impulses appears in the drivers of rhythm of the III order (His' bundle, atrioventricular the drivers of rhythm of the III order (His' bundle, atrioventricular fascicle, fasciculus atrioventricularis and pedunculi of it), fascicle, fasciculus atrioventricularis and pedunculi of it), frequency of heartbeat frequency of heartbeat lesser than 40 per minutelesser than 40 per minute..

Reason and mechanisms of development Reason and mechanisms of development of sinus tachy- and bradycardiaof sinus tachy- and bradycardia

► Sinus tachycardia and bradycardia Sinus tachycardia and bradycardia relate to relate to the group the group of nomotopic arrhythmias, connect of nomotopic arrhythmias, connect with violations of function of automatismwith violations of function of automatism..

► A capacity for automatic formation of A capacity for automatic formation of impulses depends on cells, located in the impulses depends on cells, located in the conducting system of heart (conducting system of heart (p-cellsp-cells) in which ) in which present spontaneous slow depolarization of present spontaneous slow depolarization of cellular membrane in the period of diastole. cellular membrane in the period of diastole.

► Frequency of generation of impulses Frequency of generation of impulses depends depends onon: :

a) a) maximal diastolic potential of these cellsmaximal diastolic potential of these cells; ; b)b) level of critical potential on a membrane level of critical potential on a membrane, ,

after which appears after which appears potential of actionpotential of action; and ; and c)c) speeds of diastolic depolarization. speeds of diastolic depolarization.

Reason and mechanisms of development of Reason and mechanisms of development of sinus tachy- and bradycardiasinus tachy- and bradycardia

Increase generating of impulsesIncrease generating of impulses.. Reasons: Reasons: a) at diminishing of level of maximal diastolic potential of cells of sinus a) at diminishing of level of maximal diastolic potential of cells of sinus

node node b) at approaching to it of maximum critical potential, b) at approaching to it of maximum critical potential, c) at multiplying speed of slow diastolic depolarization. c) at multiplying speed of slow diastolic depolarization.

Such phenomenon is observed: Such phenomenon is observed: a) under act of the promoted temperature of body a) under act of the promoted temperature of body b) stretching areas of sinus node, b) stretching areas of sinus node, c) under act of mediators of sympathetic system.c) under act of mediators of sympathetic system. Opposite, Opposite, a) diminishing of speed of slow diastolic depolarization, a) diminishing of speed of slow diastolic depolarization, b) hyperpolarization in a diastole and b) hyperpolarization in a diastole and c) the decreasing of critical maximum potential, as it is observed at c) the decreasing of critical maximum potential, as it is observed at

annoying a vagus nerve, are accompanied deceleration of generation annoying a vagus nerve, are accompanied deceleration of generation of impulses, and consequently - of impulses, and consequently -

The instability [fluctuation, variation] of tone of vagus nerve during The instability [fluctuation, variation] of tone of vagus nerve during the act of breathing predetermine respiratory arrhythmia (become the act of breathing predetermine respiratory arrhythmia (become more frequent palpitation at inhalation, deceleration - at exhalation). more frequent palpitation at inhalation, deceleration - at exhalation).

Children have respiratory arrhythmia in a normChildren have respiratory arrhythmia in a norm, sometimes it , sometimes it also observed for adults.also observed for adults.

Tachycardia developsTachycardia develops

Bradycardia developsBradycardia develops

Arrhythmias, related to violations of excitabilityArrhythmias, related to violations of excitability The main reason is appearance so-called ectopic hotbed of excitations which generate premature impulsespremature impulses.The most widespread arrhythmias of this group are:

a) extrasystole [beat] a) extrasystole [beat] and and b) paroxysmal [recurrent, reentrant] tachycardia.b) paroxysmal [recurrent, reentrant] tachycardia.

Extrasystole is a type of arrhythmias, which are stipulated violations of function of excitability which shows up the origin of premature contraction of heart or only ventricles. In dependence on localization of hotbed which an premature impulse goes out from, distinguish the followings types of extrasystole:

a) a) sinussinus (or nomotopic), (or nomotopic), b)b) atrial atrial, , c)c) atrio-ventricular atrio-ventricular and and d)d) ventricular [ventricular premature beats]. ventricular [ventricular premature beats].

As a wave of excitation, which arose up in an unusual place, spreads in the changed direction, it is reflected on the structure of the electric field of heart and finds a reflection on an electrocardiogram.

Extrasystoles Extrasystoles ((ESES))• When an action potential from a

supraventricular ectopic focus is transmitted to the ventricles (atrial or nodal extrasystole), it can disturb their regular (sinus) rhythm (supraventricular arrhythmia). An atrial ES can be identified in the ECG by a distorted (and premature) P wave followed by a normal QRS complex. If the action potential originates in the AV node (nodal ES), the atria are depolarized retrogradely, the P wave therefore being negative in some leads and hidden within the QRS complex or following it (1, blue frame). Because the sinus node is also often depolarized by a supraventricular ES, the interval between the R wave of the ES (= RES) and the next normal R wave is frequently prolonged by the time of transmission from ectopic focus to the sinus node (postextrasystolic pause). The intervals between R waves are thus: RES–R > R–R and (R–RES + RES–R) < 2 R–R ( 1 ). An ectopic stimulus may also occur in a ventricle (ventricular extrasystole → 2, 3). In this case the QRS of the ES is distorted. If the sinus rate is low, the next sinus impulse may be normally transmitted to the ventricles (interposed ES; 2). At a higher sinus rate the next (normal) sinus node action potential may arrive when the myocardium is still refractory, so that only the next but one sinus node impulse becomes effective (compensatory pause). The R–R intervals are: R–RES +RES–R = 2 R–R.

Ectopic Origin of Stimulus (1–5)

Abnormal Conduction (5)

Sinus extrasystoleSinus extrasystole• Sinus extrasystole arises up

as a result of premature excitation part of cells of sinus node. On ECG: shortening interval TP.

• As a result shortening of diastole and diminishing of filling of ventricles a pulse wave is diminished too.

Atrial Atrial extrasystolesextrasystoles

• Atrial extrasystolesAtrial extrasystoles are observed at presence of hotbed of ectopic excitation in the different areas of atrium and are characterized: a) change the form P-waveform P-wave (reduced, two-phase, reduced, two-phase,

negativenegative); b) at the stored complex QRS and c) some lengthening of diastolic interval after extrasystole (an incomplete compensate pauseincomplete compensate pause).

Atrio-Atrio-ventricular ventricular extrasystolextrasystol

ee

• Atrio-ventricular extrasystole is observed in case of occurring of additional impulse in atrio-ventricular node.

• The wave of excitation, which goes out from overhead and middle parts of node, spreads in two directions:

a) into ventricles - as normal b) into atrium - retrograde direct. Thus: a) the negative negative P-waveP-wave can be present before or lay before or lay on complex QRSon complex QRS; b) diastole interval after a extrasystole is a little prolonged. A extrasystole can be accompanied simultaneous beat of atrium and

ventricles. • At a atrio-ventricular extrasystole which goes out from lower part of

node, there is a compensate pause, the same, as well as at a ventricular extrasystole and P-wave is negative and situated after complex QRS.

Ventricular extrasystoleVentricular extrasystole

• Ventricular extrasystoleVentricular extrasystole are characterized presence of a complete complete compensate pausecompensate pause after premature heartbeat and deformation complex QRS.

• Next beat of ventricles arises up only Next beat of ventricles arises up only after arrival to them of duty normal after arrival to them of duty normal impulseimpulse.. That is why duration of a compensate pause equals duration of two normal diastolic pauses. However if reductions of heart are so rare that to the moment of arrival of duty normal impulse ventricles have time to go out from the state of adiphoria, a compensate pause is absent. Premature heartbeat gets in an interval between two normal and in this case called the inserted extrasystole.

• 1) Atrial ectopic beatsAtrial ectopic beats appear as early (premature extrasystoles) and abnormal P-waves in the ECG; they are usually followed by normal QRS-complexes. Following the premature beat there is often a compensatory interval. A premature beat in the left ventricle is weak because of inadequate venous return, but after the long compensatory interval, the post-extrasystolic contraction (following a long venous return period) is strong due the Starling´s law of the heart. - Adrenergic b-blockers are sometimes necessary.

• 2) Ventricular ectopic beatsVentricular ectopic beats (extrasystoles) are recognized in the ECG by their wide QRS-complex (above 0.12 s), since they originate in the ventricular tissue and slowly spread  throughout the two ventricles without passing the Purkinje system.  The ventricular ectopic beat is recognized by a double R-wave. The classical tradition of simultaneous cardiac auscultation and radial artery pulse palpation eases the diagnosis. Now and then a pulsation is not felt, and an early frustraneous beat is heard together with a prolonged interval. A beat initiated in the vulnerable period may release lethal ventricular tachycardia, since the tissue is no longer refractory.

Paroxysmal tachycardiaParoxysmal tachycardia• Paroxysmal tachycardiaParoxysmal tachycardia is arrhythmia, which is stipulated

violations of function of excitability, which shows up the origin of group of extrasystoles which fully repress a physiology rhythm.

• At paroxysmal tachycardia the normal rhythm of heart is normal rhythm of heart is suddenly brokensuddenly broken by attack of beats with frequency from 140 to 250 shots per minute.

• Duration of attack can be different - from a few secondsfew seconds to a few minutesfew minutes. It is suddenly stopped and recommences normal rhythm.

Paroxysmal supraventrical tachycardia

Paroxysmal supraventricular tachycardia: note accelerated rate and narrow QRS complexes.

Arrhythmias, related to violation of Arrhythmias, related to violation of conductivity of impulses conductivity of impulses

Select two groups of such arrhythmias: Select two groups of such arrhythmias: 1) Heart block. 1) Heart block. 2) Increased conducting of impulses – 2) Increased conducting of impulses – WPW-syndromeWPW-syndrome (Wolf-Parkinson- (Wolf-Parkinson-

White block) White block) Heart blocksHeart blocks are arrhythmias, conditioned are arrhythmias, conditioned deceleration or complete deceleration or complete

stopped conducting of impulsesstopped conducting of impulses on the conducting system. on the conducting system. ReasonsReasons: : a)a) the damage of conductive ways, the damage of conductive ways, b)b) worsening of other functional descriptions worsening of other functional descriptions, which is accompanied , which is accompanied

deceleration or complete stopped conducting of impulse.deceleration or complete stopped conducting of impulse. Violations of conductivity can Violations of conductivity can arise up: arise up: a)a) between a sinus node and atriums between a sinus node and atriums b)b) inwardly atriums, inwardly atriums, c)c) between atriums and ventricles and between atriums and ventricles and d)d) in one of legs of His' bundle. in one of legs of His' bundle. Followings types of blockades select: Followings types of blockades select: 1)1) intraatrial intraatrial; ; 2)2) atrio-ventricular; atrio-ventricular; 3)3) intraventricular intraventricular..

SA BLOCKSA BLOCK

Rate normal or bradycardia

P wave those present are normal

QRS normal

Conduction normal

Rhythm basic rhythm is regular*

Atrio-Atrio-ventricular ventricular

blockblock Four typesFour types of of

atrio-ventricular atrio-ventricular (AV)-block. From (AV)-block. From above above downwards: downwards:

First-degree AV-First-degree AV-block, block,

Second-degree Second-degree Mobitz I block Mobitz I block (Wenchebach), (Wenchebach),

Second-degree Second-degree Mobitz II block, Mobitz II block, andand

Complete AV-Complete AV-block.block.

Increase conducting Increase conducting

of impulsesof impulses

• WPW-syndrome – characterized the speed-up conducting of impulses from atriums to the ventricles, as a result there is premature excitation of the last, tachycardia develops, the interval of PQ diminishes on an electrocardiogram.

Re-entry mechanismRe-entry mechanism Under normal conditions, an Under normal conditions, an

electrical impulse is conducted electrical impulse is conducted through the heart in an orderly, through the heart in an orderly, sequential manner. The sequential manner. The electrical electrical impulse then dies out and does not impulse then dies out and does not reenter adjacent tissuereenter adjacent tissue because because that that tissue has already been depolarized tissue has already been depolarized and is refractory to immediate and is refractory to immediate stimulationstimulation. However, under certain . However, under certain abnormal conditions, an impulse can abnormal conditions, an impulse can reenter an area of myocardium that reenter an area of myocardium that was previously depolarized and was previously depolarized and depolarize it again. There three depolarize it again. There three conditions are the necessary for this conditions are the necessary for this mechanism beginning: mechanism beginning:

1 – two conductive ways are the 1 – two conductive ways are the functionally or anatomically functionally or anatomically disconnected; disconnected;

2 – some conductive way is 2 – some conductive way is blocked;blocked;

3 – the antegrade conductive way 3 – the antegrade conductive way is blocked, but the retrograde one is blocked, but the retrograde one is preserved.is preserved.

So, in that condition impulse (or So, in that condition impulse (or impulses) travels numerous through impulses) travels numerous through some area of conductive system and some area of conductive system and returns through another pathway to returns through another pathway to the reactivated myocardiocytes.the reactivated myocardiocytes.

Excitation in Electrolyte Disturbances

Hyperkalemia (> 6.5 mmol/L): Hypokalemia (< 2.5 mmol/L):

Hypercalcemia (> 2.75 mmol/L total calcium)

Hypocalcemia (< 2.25 mmol/L total calcium)

Arrhythmias with violation of functions Arrhythmias with violation of functions

of excitability and conductivityof excitability and conductivity 1) 1) atrial flutteratrial flutter (frequency of (frequency of

atrium beats - atrium beats - 250-400250-400 / / min).min).

2) 2) Atrial fibrillationAtrial fibrillation (frequency of impulses (frequency of impulses which arise up in atrium is which arise up in atrium is 400-600400-600 / min). / min).

► Atrial flutterAtrial flutter and and fibrillation have identical fibrillation have identical reasons of development reasons of development and can pass one to and can pass one to another. So, these two another. So, these two types of violation of types of violation of rhythm of heart combine rhythm of heart combine into one and called is into one and called is fibrillationfibrillation..

3) 3) ventricle flutterventricle flutter (frequency (frequency of ventricle beat is of ventricle beat is 150-150-300300/m)./m).

4) 4) FibrillationFibrillation of ventriclesof ventricles (frequency of impulses in (frequency of impulses in ventricles is ventricles is 300-500 300-500 / / min).min).

► Arrhythmias Arrhythmias which arise up as a result of simultaneous violation of functions which arise up as a result of simultaneous violation of functions of of excitability excitability and and conductivityconductivity. . To them belong:To them belong:

Even when the stimulus formation in the sinus

node is normal, abnormal ectopic

excitations can start from a focus in an

atrium (atrial), the AV node (nodal), or a

ventricle (ventricular).

ECGs (lead II) showing

abnormal rhythms

A:Respiratory sinus arrhythmia. B:Sinus arrest with vagal escape. C:Atrial fibrillation.D:Premature ventricular complex. E:Complete atrioventricular block.

Self-AssessmentSelf-AssessmentMultiple Choice QuestionsMultiple Choice Questions

I. Each of the following five statements have True/False options:I. Each of the following five statements have True/False options: Stem statement: The ventricular action potential isStem statement: The ventricular action potential isA.A.   initiated by rapid entry of Na+.   initiated by rapid entry of Na+.B.B.   characterised by slow Ca2+ -Na+- channels.   characterised by slow Ca2+ -Na+- channels.C.C.   characterised by closed K+- channels in phase 3.   characterised by closed K+- channels in phase 3.D.D.   dependent upon Ca2+-influx.   dependent upon Ca2+-influx.E. E.   independent of the Na+-K+ -pump in phase 4.   independent of the Na+-K+ -pump in phase 4. II. Each of the following five statements have True/False options:II. Each of the following five statements have True/False options:A.A. In myocardial cells, as in nerve and skeletal muscle cells,  K+ plays a minor role in In myocardial cells, as in nerve and skeletal muscle cells,  K+ plays a minor role in

determining the resting membrane potential.determining the resting membrane potential.BB. The impulse propagates from the sinus node via five bundles of internodal syncytial cells . The impulse propagates from the sinus node via five bundles of internodal syncytial cells

through the left and right atrial wall to the atrioventricular node.through the left and right atrial wall to the atrioventricular node.C.C. The long absolute refractory period of the ventricular cells,  covers the whole shortening The long absolute refractory period of the ventricular cells,  covers the whole shortening

phase of the contraction, where all the fast Na+-channels are voltage-inactivated. As a phase of the contraction, where all the fast Na+-channels are voltage-inactivated. As a consequence, no stimulus is sufficient regardless of size.consequence, no stimulus is sufficient regardless of size.

D.D. The fast Na+-influx causes phase 0 of atrial- , ventricular- , and Purkinje- action potentials. The fast Na+-influx causes phase 0 of atrial- , ventricular- , and Purkinje- action potentials. The fast Na+-channels are both voltage- and time-dependent.The fast Na+-channels are both voltage- and time-dependent.

E. E.  Noradrenaline activates a-adrenergic constrictor receptors in the coronary vessels,  Noradrenaline activates a-adrenergic constrictor receptors in the coronary vessels, whereas adrenaline activates b-adrenergic vasodilatator receptors. whereas adrenaline activates b-adrenergic vasodilatator receptors.

III.III. The following five statements have True/False options.The following five statements have True/False options.A.A. WPW-syndrome or Wolf-Parkinson-White block is caused by a short cut through an extra WPW-syndrome or Wolf-Parkinson-White block is caused by a short cut through an extra

conduction pathway from the atria to the ventricles.conduction pathway from the atria to the ventricles.BB. Atrial fibrillation is more malignant than ventricular fibrillation.. Atrial fibrillation is more malignant than ventricular fibrillation.C.C. All pacemaker abnormalities arise in the sinus node. All pacemaker abnormalities arise in the sinus node.DD. Premature beats are also called atrial ectopic beats.. Premature beats are also called atrial ectopic beats.EE. Only few cardiac arrhythmias can lead to atrial fibrillation and flutter.. Only few cardiac arrhythmias can lead to atrial fibrillation and flutter.

Try to solve Try to solve the problems the problems

before before looking up the looking up the

answersanswers

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