EKG Abnormalities Adapted from: http://www.bem.fi/book/19/19.htm Some key terms: Arrhythmia-an abnormal rhythm or sequence of events in the EKG Flutter-rapid depolarizations (and therefore contractions) of the heart muscle. While rapid, the contractions are still coordinated and effective. Fibrillation-rapid depolarizations and partial contractions of different parts of heart muscle at different times. This results in uncoordinated contraction of the heart muscle, leading to ineffective contraction, and no blood pumping. Pacemaker: A cell or group of cells that generate a rhythm of depolarization to cause the heart, or a certain region of the heart, to be excited/contract at a certain rhythm or pace. Ectopic foci: Cells other than those in the SA node that can generate their own rhythm, without input from the SA node. Remember that all cells in the electrical conduction system are autorhythmic: they can generate their own pace theoretically. However, they are usually controlled by the SA node since the SA node has a faster rate, typically. Ectopic foci are pacemaker cells whose rhythm is now faster than the SA node. Sinus rhythm: Any rhythm of electrical activity of the heart that originates in the sinus node in the right atrium (that is, the SA/sinoatrial node). Tachycardia: Faster heart rate at rest (>100 bpm) Bradycardia: Slow heart rate at rest (<60 bpm) 1
Normal sinus rhythm Normal sinus rhythm is the rhythm of a healthy normal heart, where the sinus node triggers the cardiac activation. This is easily diagnosed by noting that the three deflections, P-QRS-T, follow in this order and are differentiable. The sinus rhythm is normal if its frequency is between 60 and 100/min.< 2
Sinus Arrthymias Sinus bradycardia 3
A sinus rhythm of less than 60/min is called sinus bradycardia. This may be a consequence of increased vagal or parasympathetic tone. Sinus tachycardia A sinus rhythm of higher than 100/min is called sinus tachycardia. It occurs most often as a physiological response to physical exercise or psychical stress, but may also result from congestive heart failure. 4
Respiratory Sinus Arrythmia Respiratory sinus arrhythmia (RSA) is a naturally occurring variation in heart rate that occurs during a breathing cycle. Heart rate increases during inspiration and decreases during expiration. Heart rate is normally controlled by centers in the medulla oblongata. One of these centers, the nucleus ambiguus, increases parasympathetic nervous system input to the heart via the vagus nerve. The vagus nerve decreases heart rate by decreasing the rate of SA node firing. This allows for the body to match blood flow to the lungs with the amount of oxygen being brought in. 5
6 Ectopic pacemakers
Atrial flutter When the heart rate is sufficiently elevated so that the isoelectric interval between the end of T and beginning of P disappears, the arrhythmia is called atrial flutter. The origin is also believed to involve a reentrant atrial pathway. The frequency of these fluctuations is between 220 and 300/min. The AV-node and, thereafter, the ventricles are generally activated by every second or every third atrial impulse (for example: 1 QRS is preceded by 2, or 3, p-waves. Atrial fibrillation 7 The activation in the atria may also be fully irregular and chaotic, producing irregular fluctuations in the baseline. A consequence is that the ventricular rate is rapid and irregular, though the QRS contour is usually normal. Atrial fibrillation occurs as a consequence of rheumatic disease, atherosclerotic disease, hyperthyroidism, and pericarditis. (It may also occur in healthy subjects as a result of strong sympathetic activation.)
Pre-mature ventricular contraction A premature ventricular contraction is one that occurs abnormally early. If its origin is in the atrium or in the AV node, it has a supraventricular origin. The complex produced by this supraventricular arrhythmia lasts less than 0.1 s. If the origin is in the ventricular muscle, the QRS-complex has a very abnormal form and lasts longer than 0.1 s. Usually the P-wave is not associated with it. Ventricular tachycardia Increased rate of ventricular contraction due to ectopic focus in the ventricle. The result is activation of the ventricular muscle at a high rate (over 120/min), causing rapid, bizarre, and wide QRS-complexes; the arrythmia is called ventricular tachycardia. The QRS complexes are wide because the depolarization is spreading very slowly through the ventricles as a result of the signal not traveling through the normal conduction pathway (bundle, purkinje fibers, etc.) 8
Ventricular fibrillation When ventricular depolarization occurs chaotically, the situation is called ventricular fibrillation. This is reflected in the ECG, which demonstrates coarse irregular undulations without discernible QRS-complexes. The cause of fibrillation is the establishment of multiple pacemakers in the ventricles, usually involving diseased heart muscle. In this arrhythmia the contraction of the ventricular muscle is also irregular and is ineffective at pumping blood. The lack of blood circulation leads to almost immediate loss of consciousness and death within minutes. The ventricular fibrillation may be stopped with an external defibrillator (AED) pulse and appropriate medication. 9
Delay at AV-node: AV node blocks First-degree atrioventricular block When the P-wave always precedes the QRS-complex but the PR-interval is prolonged over 0.2 s, first-degree atrioventricular block is diagnosed. Second-degree atrioventricular block If the PQ-interval is longer than normal and the QRS-complex sometimes does not follow the P-wave, the atrioventricular block is of second degree. 10
Third-degree atrioventricular block Complete lack of synchronism between the P-wave and the QRS-complex is diagnosed as third-degree (or total) atrioventricular block. The p-wave and the QRS complex occur at totally independent/different rhythms. The conduction system defect in third degree AV-block may arise at different locations such as: Over the AV-node In the bundle of His Bilaterally in the upper part of both bundle branches 11
One last weird one: Heart rhythms starting at AV node Junctional rhythm The heart rate should usually start at the SA node (this is called a sinus rhythm). If the heart rate begins at the AV node, this is called a junctional rhythm. The AV node beats more slowly than the SA node. For a junctional rhythm, the heart rate is slow (40-55/min), the QRS-complex is normal, the P-waves are possibly not seen. Because the origin is in the junction between atria and ventricles, this is called junctional rhythm. Therefore, the activation of the atria occurs retrograde (i.e., in the opposite direction). Depending on whether the AV-nodal impulse reaches the atria before, simultaneously, or after the ventricles, a P- wave will be produced before, during, or after the QRS-complex, respectively. If it reaches the atria after the ventricles, the P- wave will be superimposed on the QRS-complex and will not be seen. 12
Treatments Defibrillators are meant to cause all cells to immediately depolarize at same time and reset ectopic foci back to rhythm of SA node. So they de-fibrillate (undo fibrillation) Ablation/killing of ectopic foci using targeted radiofrequency waves can treat certain fibrillations or flutters. You re not resetting foci, you re KILLING off rogue autorhythmic cells 13