![]() This is characterized by a tachycardia where the P wave configuration differs from the sinus P waves. Supraventricular Tachycardia (SVT)-Atrial or Junctional The QRS complexes are narrow upright complexes in lead II and look similar to the sinus complexes. The P waves may be positive, negative or hidden in the QRS complexes. These are supraventricular complexes that occur early and arise from a focus in the atria or the AV node junctional area rather than from the sinus node. Supraventricular Premature Complexes (SVPC) Animals in pain or with pyrexia may also show a persistent sinus tachycardia.ĭisturbances of Supraventricular Impulse Formation Animals with incessant tachycardia may well have underlying congestive heart failure with high sympathetic drive. Sinus tachycardia is probably the most common rhythm detected in small animal cardiac patients due to the excited state of most patients. The recommended protocol is to record an ECG trace, then administer atropine (0.04 mg/kg by subcutaneous injection) and after 30 minutes record a further ECG trace. If these bradyarrhythmias are genuinely related to high vagal tone, they should be easily abolished by the administration of atropine. It may also be recognised in patients with hypothermia, hyperkalaemia, CNS lesions, or drug related, e.g., digoxin, opioids, beta blockers, calcium channel antagonists. Periods without evidence of any sinus node activity may be prolonged enough to result in syncope. It is usually recognised in dogs with high vagal tone such as brachycephalic dogs or dogs with underlying respiratory disease. Sinus arrest is a period where there is no evidence of atrial activity for a period in excess of the two preceding R-R intervals, and implies that there is a depression in automaticity within the sinus node. This lecture will focus on the identification of arrhythmias and the treatment options. In patients with sick sinus syndrome, or complete or high-grade AV block, a permanent pacemaker is indicated.Arrhythmia can be divided into disturbances in impulse formation and impulse conduction which may result in bradyarrhythmias or tachyarrhythmias. In the pediatric population, persistent symptomatic junctional tachycardia is an indication for percutaneous radiofrequency ablation. If a patient is refractory to these pharmacologic treatments and goes into junctional tachycardia, intravenous phenytoin can be administered in a monitored setting as these patients can develop hypotension. In the setting of digoxin toxicity, a patient must be treated with atropine and digoxin-specific antibody. Otherwise, healthy individuals who have junctional rhythm and are asymptomatic need no medical management as the rhythm is usually a result of their increased vagal tone suppressing the SA node intrinsic automaticity. Therefore, before establishing a management plan for patients presenting with a junctional rhythm, an underlying etiology must be determined first. In circumstances where the junctional rhythm is a result of underlying sinus node dysfunction that is leading to asystole or bradycardia, it should not be terminated, for it is maintaining the heart rate. ![]() Treatment of a junctional rhythm primarily depends on the underlying cause of the rhythm. The terminology used to identify the type junctional rhythm depends on its rate and is as follows: This electrical activity then travels through the atria to the AV node from where it reaches the Bundle of His from where the electrical signals travel to the ventricles through the Purkinje fibers. Generally, in sinus rhythm, a heartbeat is originated at the SA node. A junctional rhythm is where the heartbeat originates from the AV node or His bundle, which lies within the tissue at the junction of the atria and the ventricle. The first septal perforator of the left anterior descending artery also supplies blood to the AV node. The blood supply to the AV node is from the AV nodal branch of the right coronary artery (90%) or the left circumflex artery (10%) depending on the right or left dominant blood supply to the heart. The sinoatrial nodal artery supplies blood to the sinoatrial node, it branches off the right coronary artery in 60% of cases, whereas in 40% of cases, it comes from the left circumflex coronary artery. This anatomic region is also commonly referred to as the triangle of Koch. It sits within an anatomic region bordered posteriorly by the coronary sinus ostium, superiorly by the tendon of Todaro, and anteriorly by the septal tricuspid valve annulus. The atrioventricular node (AV) is a subendocardial structure situated in the inferior-posterior right atrium. ![]() The sinoatrial node (SA) is the default pacemaker and is located subepicardially and is crescent in shape.
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