Pit Bull 101: Heart Conditions: ArrythmiaApr 27 2014
What can cause these abnormally rapid heart rates?
Some dogs have abnormally rapid heart rates, which can be caused by an extra connection between the upper chambers (the atria which receive blood from the body) and the pumping chambers (ventricles), by an abnormally firing focus within the upper chambers, by an abnormal electrical circuit within those upper chambers, or by an extra pathway within the normal conduction system. The abnormally rapid heart rate does not allow the pumping chambers to efficiently fill with blood; therefore, less blood is pumped to supply the needs of the tissues. If the abnormal rhythm is sustained, heart failure and secondary heart muscle disease can result. Both of these complications are potentially reversible with adequate rhythm control. Another problem can occur if an extra connection (accessory pathway) is able to conduct in a forward direction. The heart’s normal conduction system imposes a delay in the passage of an impulse from the receiving chambers to the pumping chambers. If the upper chambers develop a rapid rhythm, the normal conduction system will not allow the ventricles to go as rapidly. An accessory pathway typically does not have this built-in mechanism to slow conduction. The pumping chambers could therefore be driven rapidly by an abnormal atrial rhythm.
What is an electrophysiology study?
General anesthesia is used throughout the study and ablation so that your animal experiences no discomfort. Your dog will be shaved over the neck, both groins, and back to prepare them for a sterile procedure. Small squares on each limb and a section across the chest will be shaved for application of ECG electrodes to monitor their electrocardiogram throughout the procedure. The neck and groin sites will be prepared with antiseptic solutions. Catheters will be introduced through the large veins in the neck and groin. These catheters will be positioned at key locations within the heart to “map” the abnormal rhythm. In order to do this, we must induce the rapid rhythm in your dog during the procedure. Various areas of the heart will be paced through the catheters in order to start and stop the abnormal rhythm prix viagra officiel france. Drugs will also be given to try to induce the arrhythmia before and/or after ablation. If the abnormal connection lies on the left side of the heart, we will need to introduce a catheter through the artery in the groin.
What is radiofrequency catheter ablation?
Radiofrequency energy for this procedure is delivered through a special cardiac system with special frequencies and characteristics for the heart. When a site believed to be the accessory pathway is found, energy is delivered through a special ablation catheter for a short period. If the abnormal rhythm is disrupted and no ill effects are observed, energy delivery is continued. After what appears to be a successful ablation, we test for 1 hour to make certain that the abnormal rhythm does not reappear during this early follow-up.
When is it best to do an ablation?
Early in the process after your dog has been diagnosed with an abnormal, rapid heart rhythm is the best time to do an electrophysiology study and ablation. We have certainly done these procedures in dogs who have had rhythm problems for years and failed multiple medications. The risk of anesthesia, however, is notably higher in those animals that have gone on to develop heart muscle disease.
What are the benefits of the procedure?
This procedure is unique in that it offers a cure for certain abnormal rhythms, rather than simply trying to decrease the number of episodes of rapid rhythm. All rhythm medications can be stopped if the ablation procedure is successful. Dogs who have heart muscle disease and heart failure secondary to their rapid rhythm are typically able to be weaned off their heart failure medications over the first 2 months after successful ablation. This procedure has the highest success rate in dogs for accessory pathways. The success rate for atrial tachycardias is considerably lower, due to the lack of safe accessibility to a large portion of the left atrium in the dog.
What are the risks of the procedure?
Complications during this procedure are rare, but can occur. Electrophysiologic studies are performed under general anesthesia, which carries the risk (albeit small) of airway irritation and even death. The likelihood of poor tolerance to anesthesia increases the worse the heart’s mechanical function becomes. Hematomas (bruises) can form at the sites where catheters are introduced into large vessels. This is more likely if the artery must be used. Excessive blood loss, which has been reported in rare human cases, could be life-threatening. If an accessory pathway or abnormal focus in the upper chamber lies near the normal conduction system, there is the possibility that the normal conduction system may be damaged during radiofrequency energy delivery. If the conduction system is damaged, a pacemaker may be needed, if permanent damage occurs. Every possible precaution is taken to avoid this complication; however it remains a possibility of which you should be aware. Other potential complications encountered very rarely in human ablation cases (not seen to date but a very rare potential in veterinary cases) are: perforation of a part of the heart with a catheter, damage to a coronary artery (resulting in the equivalent of a “heart attack”), and clot formation within a portion of the heart.