6th Lecture 2024.pdf

Medical Instrumentation Y ECTS - B.Sc. in Biomedical Engineering LESSON 6 The Arrhythmias Prof. Carlo Ricciardi– Prof. Alfonso Maria Ponsiglione HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIV...

Medical Instrumentation Y ECTS - B.Sc. in Biomedical Engineering LESSON 6 The Arrhythmias Prof. Carlo Ricciardi– Prof. Alfonso Maria Ponsiglione HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Coronary artery disease Coronary artery disease is a common heart condition that involves atherosclerotic plaque formation in the vessel lumen. This leads to impairment in blood flow and thus oxygen delivery to the myocardium. Classification of coronary artery disease is typically done as under: Stable ischemic heart disease (SIHD) Acute coronary syndrome (ACS) o ST-elevation MI (STEMI) o Non-ST elevation MI (NSTEMI) o Unstable angina HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  1 Ischemia The capacity of coronary blood vessels to supply nutrients and oxygen to the contractile heart muscle decreases in presence of ischemia. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY 2 ST-segment leveling HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Heart Rate Heart rate is the number of beats per minute (bpm). The normal heart rate of a healthy adult man is approximately 70 bpm. A slower rate is called bradycardia (< 60 bpm). A fast rhythm is called tachycardia (> 100 bpm). An “abnormal” rhythm is an arrhythmia. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY Bradycardia and tachycardia https://www.youtube.com/watch?v=ZMLyRdhcidQ HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY 1 Cardiac arrhythmias Cardiac arrhythmias are due to pathological changes in the cardiac impulse generation or conduction system. There are many mechanisms that generate these phenomena. Impulse generation disorders result in a change in sinus rhythm. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY 2 Cardiac arrhythmias Cardiac arrhythmias are due to an electrical instability associated with abnormal mechanical activity of the heart Arrhythmias can interfere with the normal circulation of oxygenated blood in the body, and, in some particular cases, block this circulation with fatal consequences. The arrhythmia can be treated in many cases with the administration of drugs, with surgery, or with impulsive electrical stimulation. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  3 Physiological conduction We recall that a normal cardiac cycle begins in the SA node where the "Pacemaker" cells give rise to an atrial depolarization front that produces the mechanical contraction of the atrium with consequent filling of the ventricle. The excitation wave arrives in the ventricle through the AV node, where, due to the low conduction velocity, it is delayed before passing into the bundle of HIS and from there to the two branches (right and left) until it reaches, through the fibers Purkinje, the ventricular heart muscle, which contracts to expel blood. During normal depolarization the two branches are activated simultaneously, producing a narrow QRS complex of approximately 60-80 ms. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY 4 Ectopic pacemakers The intrinsic rhythm of ectopic pacemakers comes into play (under abnormal conditions) when: their frequency has increased the fastest pacemakers are depressed the conduction system from the SA node is interrupted ectopic focus is activated. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY 5 Ectopic beats Ectopic beats are generated by parts of heart tissue with abnormal self-excitation abilities. They can be generated from "focal" points in the atria or ventricles. The ectopic beats that are generated in the atria generally produce altered P waves, due to different excitation pathways and therefore to the different activation sequence of the myocardial fibers (QRS complexes are instead normal). The ectopic beats that are generated in the ventricles, necessarily premature, produce very strange waveforms, due to the widely different paths of excitation and activation. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  6 Site of the ectopic focus If a depolarization wave originates in a site other than the sinus node, an arrhythmia is generated. When the origin of the beat is in the atrium but not in the sinus node, it is called atrial arrhythmia. The shape of the QRS complex generated by a depolarization wave originating in the atrium outside the sinus region is usually similar to that of a QRS complex generated by a depolarization wave originating in the sinus node, although it may appear prematurely and is preceded by a P wave that has a different shape than normal. When the source of the beat is in the atrium and near the atrioventricular node, the resulting arrhythmia is also called supraventricular (atrial arrhythmia is a subgroup of supraventricular arrhythmias). If the point of origin of the depolarization is in the ventricles, the arrhythmia is called ventricular. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  7 Cardiac arrhythmias and cardiac output A ventricular or supraventricular arrhythmia with an abnormal PR interval very often leads to a reduction in cardiac output. Obviously, a single ectopic beat has a small effect on mean cardiac output, but frequent and repeated ectopic beats can considerably reduce or in some cases block blood circulation. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY 8 «Return» phenomenon Among the phenomena responsible for arrhythmias, the return should be mentioned. When the excitation wave branches in multiple paths along the cardiac fibers, the excitation coming from opposite directions stops (annihilation) because the cells, just excited by one wave, cannot immediately be excited by the other. Similarly, the excitation is stopped in the bidirectional block. When a one-way block situation occurs in a path for which the retrograde impulse is delayed at least as long as the refractory period of the action potential, a premature activation occurs. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY «Return» phenomenon A: normal path with annihilation along path C B: block of the action potential in that path C: delay in the right side (due to the block) with respect to the left one => asimmetric conduction D: partial block in the right side => the action potential come back and originates a premature contraction HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Cardiac arrhythmias Due to abnormalities in the origin of the heartbeat HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY Sinus arrhytmia It is an accentuation of the normal heart rhythm variability, often related to coronary artery disease. The impulses originate in the sinus node (hence the sinus attribute). The P - QRS - T waves of each cycle are usually normal and identical in location and morphology, but the succession of cycles is very irregular. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY Migrant pacemaker It is a variable rhythm due to the change in the location of the pacemaker. In this situation, activity shifts from one ectopic focus to another. P waves have a different morphology depending on the site of pacemaker activity. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Premature atrial systole Premature atrial systole are contractions of the atria that are triggered by the atrial myocardium but have not originated from the SA node. It causes the appearance of an abnormal and anticipated P wave. Atrial premature systole originates in an ectopic focus in the atrium, thus giving to the P waves a different morphology. The ectopic impulse depolarizes the other sites in the same way as a normal impulse, so that the AV node receives and transmits the impulse in turn, thus having a normal QRS. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Nodal premature systole It originates from an ectopic discharge of the AV node, which is activated before the SA node begins a normal cycle. Therefore, it is possible to detect the appearance of a normal QRS, which occurs well in advance, and is generally not preceded by a P wave. Nodal ectopic beats can also lead to retrograde stimulation of the atria, so the P wave can be negative, or displayed shortly after the QRS complex. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  1 Premature ventricular contraction It originates from an ectopic focus in a ventricle. The ectopic ventricular impulse, like all other premature impulses, occurs much earlier in the cycle. The resulting premature ventricular contraction, usually known as PVC, it is easily recognizable in the electrocardiographic tracing. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  2 PVC A PVC does not follow the usual conduction system of bundle branches of His, so the conduction is slowed down (very wide QRS). Indeed, the heartbeat is initiated by the Purkinje fibers rather than the SA node. Everywhere the impulse of the PVC originates in the myocardium, the cells will conduct the stimulus very slowly. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  3 PVC (or extra-systole) The PVC has the following ECG features: Broad QRS complex (≥ 120 ms) with abnormal morphology Premature — i.e. occurs earlier than would be expected for the next sinus impulse Discordant ST segment and T wave changes. Usually followed by a full compensatory pause Retrograde capture of the atria may or may not occur HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Interpolated Beats - Bigeminy and Trigeminy The PVC may occasionally be associated with one or more normal cycles, and this behavior will occur many times. The interpolated beats are PVC interposed between two normal beats; they are not followed by a compensatory pause and do not modify the basic rhythm. When a PVC is associated with a normal systole, we speak of bigeminy. A PVC associated with two normal systoles is called trigeminy. And, similarly, for quadrigeminism. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Atrial fluctuation/flutter In atrial fluctuation, an ectopic focus located in the atria is activated at a frequency of 250-350 beats per minute, causing a rapid succession of atrial depolarizations, each morphologically identical to the others, but which in reality are not P waves but fluctuation waves. Only occasionally the atrial stimulus will stimulate the AV node, so that some wave fluctuations appear in series before there is a QRS complex. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Atrial fluctuation/flutter ECG features of the atrial fluctuation are the following: Undulating saw-toothed baseline F (flutter) waves Atrial rate 250-350 beats/min Regular ventricular rhythm Ventricular rate typically 150 beats/min (with 2:1 atrioventricular block) 4:1 is also common (3:1 and 1:1 block uncommon) HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY 1 Atrial fibrillation Atrial fibrillation is due to the activation of multiple foci in the atria. No single impulse can completely depolarize the atria, and only occasionally does an impulse reach the AV node; no true P wave can be found. A few waves of fluctuation appear in series before there is a QRS complex. ECG features of the atrial fibrillation are the following: P waves absent; oscillating baseline f (fibrillation) waves Atrial rate 350-600 beats/min Irregular ventricular rhythm Ventricular rate 100-180 beats/min HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY 2 Atrial fibrillation HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY 3 Atrial fibrillation HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Ventricular fluctuation Ventricular fluctuation is determined by a ventricular focus that discharges electrical stimuli at a rate of 200-300 per minute; extremely high frequency and very dangerous. ECG features of ventricular fluctuation are the following: Very broad complexes (>160ms) Absence of typical RBBB or LBBB morphology Extreme axis deviation (“northwest axis”) AV dissociation (P and QRS complexes at different rates) Ventricular fluctuation evolves into fatal arrhythmias. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  1 Ventricular fibrillation A true ventricular fluctuation almost invariably progresses to ventricular fibrillation (chaotic ventricular depolarization) requiring cardiopulmonary resuscitation and defibrillation. ECG features of ventricular fibrillation are the following: Fibrillation waves of varying amplitude and shape. No identifiable P waves, QRS complexes, or T waves Heart rate anywhere between 150 to 500 per minute HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  2 Ventricular fibrillation Arrhythmias originating from the ventricular myocardium or His- Purkinje system are grouped under ventricular arrhythmia. This includes a subset of arrhythmias such as ventricular tachycardia, ventricular fibrillation, PVC, and ventricular flutter. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Cardiac arrhythmias Due to blockages in the electrical conduction system HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  I, II and III degree blocks First-degree AV block is characterized by a slow propagation of the AV node, P-R interval greater than 0.20 s. (1) First-degree AV block is present when the P-QRS-T sequence is normal, but the P-R interval is increased. Second-degree AV block is present when there are 2 or more atrial pulses (and corresponding P-waves on the ECG tracing) for each ventricular response (QRS complex) 2:1 (2a) or 3:1 block (2b). In third-degree AV block, the atrial rate (P waves) and ventricular rate (QRS) are independent. (3) This behavior is called AV dissociation. The ventricles, without stimulation, establish their own rate (30-40/minute), or are stimulated by the AV node. (1) (2b) (3) (2a) HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Branch block When bundle branch block is present, either the right or left ventricle may activate delayed, depending on the site of the block. Ventricular depolarization of both is of normal duration. The physiologic electrical conduction system of the heart, specifically in the His-Purkinje system, is altered or interrupted. The result is the enlarged aspect of the "QRS" depending on the non-simultaneous activation. Since the "widened QRS" is due to asynchronous depolarization of both ventricles, two R waves can usually be seen. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY Cardiac blocks HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY Treatment of arrhythmias The need for treatment of arrhythmias depends on the symptoms and severity of the arrhythmia. Possible interventions: antiarrhythmic drugs; pacemaker - in case of arrhythmias that lower the rhythm; defibrillator (provides an electric shock that "resets" the electrical system of the heart) - useful in case of flutter or fibrillation; ablation of the areas where ectopic foci arise (with internal catheter); a combination of the above-mentioned. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Ablation Transcatheter ablation is a minimally invasive procedure during which small portions of the heart are eliminated, "burned". Doctors insert a thin, flexible tube (catheter) into blood vessels and maneuver it into the heart, disrupting the abnormal electrical pathways in the heart tissue. It is mainly adopted in the event that the patient is affected by atrial fibrillation not controlled by drug therapy. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY 1 Pacemaker If the cardiac electrical stimulus conduction system malfunctions, an artificial heart stimulator (pacemaker) can take over the function of controlling the heartbeat. Pacemakers are able to "feel" the electrical activity of the heart and, when this is absent, they deliver electrical stimuli. A pacemaker is a titanium device about a few centimeters in size that is implanted under the skin in the chest. Inside the casing are the battery and the electronic device. The pacemaker is connected to the myocardium via a probe. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  2 Pacemaker The types of pacemakers are identified by 3 to 5 letters, which represent: which heart chambers are stimulated (A, V, D=double) which heart chambers are “felt” (A, V, D) how the pacemaker responds to a felt event - inhibits or activates stimulation (O=none, I=inhibits, T=trigger, D) if the pacemaker is able to increase the pacing rate - frequency modulation (O=not programmable, R=programmable) if the stimulation is multisite (O, A, V, D) - in both atria - in both ventricles - more than one lead in a single chamber HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY Pacemaker HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY Defibrillators Defibrillators are devices used to deliver high-intensity, short-duration electrical shocks through the patient's chest, to restore the normal heart rhythm. HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Defibrillator Normal heart rhythm (a), with a beating frequency within the range necessary for the heart to get enough blood into the circulation. Ventricular fibrillation (b), the electrical activity is asynchronous and due to the contraction of many ventricular fibers: the cardiac output is insufficient. The defibrillator is also used for the correction of arrhythmias related to myocardial hyperexcitability: atrial fibrillation (c) flutter (d) paroxysmal tachycardias (e). HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY Defibrillator: electrodes positioning HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY  Defibrillation “Defibrillation depends on the successful selection of energy to generate sufficient current flow through the heart (trans-myocardial current) to achieve defibrillation, while causing minimal damage to the myocardium". American Heart Association. Circulation. 2000:1029(suppl I):I-90-I-94. Ready?... Go!!! HÁSKÓLINN Í REYKJAVÍK | REYKJAVIK UNIVERSITY