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Originally appeared as Ask the Vet by Dr. Shawn Ashley in Pug Talk Magazine (May/June/93 & July/Aug/92) Heatstroke is defined as a hyperthermic condition resulting in direct thermal injury to tissues. At risk are animals participating in strenuous activity or those confined in hot humid environments with decreased ventilation and limited access to water; conditions common in the southern United States. Other predisposing factors include obesity, cardiovascular disease, central nervous system disease, extremes of age, and prior heatstroke episodes. Drugs such as tranquilizers, hormones, and heart medications can also predispose to thermoregulatory difficulties. Brachycephalic breeds (which includes Pugs) are prone to heatstroke due to physical characteristics that impair ventilation and beat dissipation. Hyperthermia occurs with acute rectal temperatures of 109.4F (43C) or persistent temperatures of 106F (41C). At these temperature heatstroke ensues with destruction of cell membranes leading to organ failure. Dehydration leads to thickening of tbe blood (hemoconcentration) and sludging of blood. This sludging of blood causes tissue hypoxia, platelet dysfunction and bleeding disorders. The sequellas of this cellular destruction, organ hypoxia, and circulatory insufficiency include muscle necrosis, liver damage, gastrointestinal tract destruction, kidney failure, and finally disseminated intravascular coagulation (a terminal bleeding disorder due to loss of clotting factors and platelets). Kidney, liver and bleeding disorders may occur within hours or several days later. The above can all lead to cerebral edema or swelling of the brain causing neuronal/brain damage, blindness, hemorrhages, convulsions and fatal seizures. Clinical signs of heatstroke include panting, stupor, convulsions, tachycardia, vomiting, diarrhea, and bright red injected gums. Treatment includes decreasing the body temperature slowly by cold water baths, mists, ice packs, and fans. The body temperature must be monitored closely or hypothermia may be induced. Ancillary therapy will be don on an emergency basis by your veterinarian. It includes intravenous fluids and drugs to control cerebal edema, shivering, shock, secondary bacterial infections, kidney failure, liver, muscle damage, and DIC. Periodic bloodwork will be necessary to monitor organ functions as the hypoxia and bleeding disorders sensitize them to problems in the immediate to long term future. In summary, heatstroke is a complex cascade of events affecting several body systems; it is medical emergency that requires proper prompt treatment.
ATRIOVENTRICULAR HEART BLOCK The heart, muscles, whole body run off electrical impulses from the brain through various pathways to the responsive organs. One such pathway is located in the heart. The cardiac conduction system consists of the sino-atrial node (SA Node) which triggers the atria of the heart to beat, to the atrioventricular node (AV Node) to the Bundle of His terminating in the Purkinje fibers, all of which regulate the beating of the ventricles of the heart. If there is any interruption in the electrical impulses the rhythm of the heart is disrupted. Clinical signs vary with the level and degree of this disruption. Sick sinus syndrome is a disruption at the level of the SA Node and is characterized by long pause between heartbeats, which lead to syncope (fainting). SA block results in very slow heart rates of 40 beats per minute or less. Sudden death resulting from arrhythmia is uncommon, but has been reported in Pugs. Atrioventricular heart block occurs at the level of the AV Node between the atria and ventricles. There are three degrees of AV Block depending on the severity. Clinical signs consist of weakness, lethargy, exercise intolerance, and other signs of congestive heart failure. Rhythm disturbances are usually seen in middle-aged or older dogs as sequelas of bacterial mendocarditis, infiltrative myocardial disease, hypertrophic cardiomyopathy, hyperkalemia, or with digitalis intoxication. First degree or mild AV block are often caused by increased vagal tone which is common in brachycephalic dog breeds. Complete heart block has also been reported as a congenital defect of Pugs. Heart blocks may be auscultated but usually are only detected by an electrocardiogram. If there is concern of a heart conduction problem it is recommended an ECG be run prior to sedation or anesthesia. Certain sedative, tranquilizers, anesthetics, and other drugs can be hypertensive and/or produce arrhythmias, thus aggravating this condition. The treatment of choice with severe heart block is an artificial pacemaker implantation after extensive diagnostics have been performed. |