![]() ![]() With this therapy medications are used to increase the heart rate (such as bronchodilators). If signs are infrequent and disease is not severe, or if pacemaker therapy is not feasible, then medical management of SSS can be considered. The battery life in modern pacemakers generally lasts for years (with some lasting the life of the patient!). It is very important that animals are restricted from activity for the first 6 weeks after pacemaker placement. Potential complications can include lead fracture, lead migration or development of a blood clot on the pacemaker lead. Pacemaker therapy is well tolerated in animals and has been shown to improve the length and quality of lives in animals with SSS. A small pacemaker generator is attached to the lead and is placed under the skin in the neck region. The pacemaker is placed via a minimally invasive surgery by introducing a pacemaker lead through the vein in the neck (jugular vein) and passing it into the right ventricle. For dogs with significant disease and clinical signs (frequent fainting – some dogs with SSS have been noted to faint over a dozen times per day!), a transvenous pacemaker is recommended. Once a diagnosis of SSS is made, treatment recommendations are based upon the severity of the disease and clinical signs. For those animals having both bradycardia and tachycardia contributing to episodes of fainting, therapy to address the bradycardia (pacemaker) is indicated before anti-arrhythmic therapy for the tachycardia is prescribed. Holters are also useful when dogs are fainting related to SSS to determine if the cause of their fainting is periods of bradycardia or tachycardia. Most dogs tolerate wearing a Holter monitor without issue. Echocardiography may be performed to rule out any structural heart changes that may be influencing the heart rhythm.Īn ambulatory ECG (called a Holter monitor – pictured to the right – these are the type of Holter monitors utilized by East Coast Veterinary Cardiology) is frequently used to evaluate dogs suspected to have SSS as it allows evaluation of heart rhythm over a full 24-hours. ![]() In animals with SSS, they typically have a suboptimal response to atropine or have no response at all. A normal atropine response test is when the heart rate doubles from the pre-treatment rates and any noted pauses resolve. This is when atropine is given to try to stimulate the SA node to assess its function. Generally, animals that are suspected to have SSS will also have an atropine response test. ![]() An ECG allows analysis of the rhythm of the heart and allows for determination of irregularities in the conduction system of the heart. SSS is diagnosed by performing an electrocardiogram (ECG). Some animals may be asymptomatic in the early stages of the disease and will be detected by a veterinarian during a routine physical examination. This further contributes to a slower than normal and irregular heart rate/rhythm.Īffected animals with SSS will typically present with signs of exercise intolerance, weakness, lethargy (sleeping more) and fainting. When the AV node becomes involved, the electrical signal is blocked and does not enter the ventricles leading to failure of activation of the ventricles. ![]() Affected animals may occasionally have periods of tachycardia (fast heart rates). Many animals with SSS will have a slower than normal heart rate with frequent pauses between heartbeats. As a result of this infiltration of the SA node it begins to depolarize haphazardly in an irregular fashion. The exact etiology is unknown, but it has been shown that in affected Schnauzers the pacemaker cells in the SA node are replaced largely by fibrous (scar) tissue. In animals with SSS there is dysfunction of the SA node and in some cases, the AV node is also involved. After the SA node depolarizes (fires), the electrical signal travels through the atria and enter the lower heart muscle chambers (ventricles) through the atrio-ventricular (AV) node. This is considered the pacemaker (command centre) of the heart and sets the rhythm and rate of the heartbeat. In a normal heart, the stimulus to cause the heart to contract originates from a collection of specialized cells called the sino-atrial (SA) node which is located within the right atrium. The Miniature Schnauzer, West Highland White Terrier and Cocker Spaniel are three breeds which are commonly diagnosed with SSS. Sick sinus syndrome (SSS) is an acquired disease of the conduction (electrical) system which is typically diagnosed in geriatric dogs. ![]()
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