Electrocardiographic Screening Statistics at the 1997 IWCA Specialty, 
Lake Placid, NY

by Neil K. Harpster, VMD

     In the non-adult classes, only a single ECG abnormality was defined. This consisted of frequent, singly occurring ventricular premature beats in a seven and one-half month old male puppy. This puppy's dam developed a uterine infection post-whelping and several puppies in the litter died. This puppy was clinically normal despite the arrhythmias.

     Among the adult Irish Wolfhounds, the incidence of ECG abnormalities was quite high with abnormalities or questionable abnormalities being present in 31.1 percent of the dogs examined (see Tables 1 and 2). The questionable abnormalities in Table 1 is the same group listed as LVH pattern in Table 2. This group of seven dogs, 5 females and 2 males, were distinguished by the presence of R waves in Lead V4 of greater than 3.8 millivolts (mV). Notice that the average R wave amplitude in V4 was nearly 2.0 mV higher than any of the other category averages (Table 1) and also that the amplitude of the R waves in Lead 2 for this group was significantly higher than in the other categories. While this ECG finding is generally associated with left heart enlargement, its significance in this group of dogs is unclear. Similar unclear conclusions can be stated for the left axis deviation and the right axis deviation categories in Tables 1 and 2. (Left axis deviation is associated with a shift of the mean electrical axis [MEA] of the electrocardiogram to the left [normal MEA in the dog ranges from +300 to +900], resulting in a MEA of +30.0^o counterclockwise to -90.0^o. These changes are usually associated with either left ventricular enlargement or a conduction abnormality involving the left ventricle. On the other hand, right axis deviation implies a shift in the MEA to the right, resulted in a plotted MEA ranging from +100.0^o clockwise to -90.0^o. This ECG pattern is commonly present with right ventricular enlargement or with conduction abnormalities affecting the right ventricle.) Our intent at the present time is to follow these dogs long term to see if they are at increased risk of developing more significant cardiac changes.

     The other ECG abnormalities listed in the Tables are the more significant ones and fall under the heading of cardiac arrhythmias. These include those listed under criterion as atrial fibrillation, supraventricular premature beats (SVP Beats), and ventricular premature beats (Vent. P Beats). Chronic atrial fibrillation was the initial arrhythmia recognized in the Irish Wolfhound breed that started us off on a search to define and better understand the "Heart of the Wolfhound". While it has become clear that the Irish Wolfhound does have a myocardial disease that is most likely genetically influenced, this disease is far less serious than many of the cardiomyopathies seen in other canine breeds.

     Atrial fibrillation was by far the most common arrhythmia recorded at this year's ECG screening, although this has not always been the finding. Of the fourteen dogs with atrial fibrillation, eight were males, and the average age was 4.21 years (range 1 to 6 years). Two of the dogs with atrial fibrillation also had ventricular premature beats. While the overall incidence of arrhythmias was comparable to the 1993 and 1995 studies, the complete absence of supraventricular premature beats was a first. A reason to explain this is unclear.

     The evolution of cardiac arrhythmias in the Irish Wolfhound, as I understand it, begins with supraventricular premature beats which are instigated by underlying myocardial disease and/or some degree of cardiac stress. In most instances the supraventricular premature beats are short lived, being replaced by atrial fibrillation. A small number of wolfhounds with atrial fibrillation also have or develop ventricular arrhythmias, and occasionally some wolfhounds have ventricular arrhythmias of varying severity without atrial fibrillation. Dogs in this latter group and those with atrial fibrillation and ventricular arrhythmias are at significant risk of sudden death, and must be monitored and followed closely.

     Based on our findings in Irish Wolfhounds over the past twenty-plus years, my current recommendations are as follows. All dogs being used for breeding MUST have a cardiac evaluation with an ECG recording a 6 to 12 month intervals, and ideally one to two months before mating.

     Echocardiographic studies are usually normal in mild to moderate disease, so an echocardiogram of a "Doppler study" is NOT a good screening tool. A long ECG tracing or a 24-hour Holter monitor study are the preferred methods for monitoring. Any dog with arrhythmias should be monitored closely and should NOT be used for breeding. Only by following this type of program along with DNA profiling, judicious breeding, cooperation and contribution to ongoing studies and complete honesty with one another can we expect to improve the "Heart of the Wolfhound" in the future.

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Abbreviations: A. Fib.=atrial fibrillation; BW=body weight in pounds; HR=heart rate; L.Axis Deviation=left axis deviation (frontal plane mean electrical axis [MEA] ranging from +30.0^o counterclockwise to -90.0^o, usually indicative of either left ventricular enlargement or the result of a conduction abnormality affecting the left ventricle); mV=amplitude of electrocardiographic deflections in millivolts; P. Beats=abnormal depolarization processes originating in either the aria of the ventricles; QRS=the electrocardiographic timing interval from the onset of ventricular depolarization to the completion of ventricular repolarization (includes both the QRS complex and the T wave); R. Axis deviation= right axis deviation (frontal plane MEA ranging from +100.0^o clockwise to -90.0o, usually suggestive of right ventricular enlargement or of a conduction abnormality involving the right ventricle); Right B.B. Block=right bundle branch block, which occurs when the major conduction pathway to the right ventricle is non-functional; R_ll=R wave amplitude recorded in Lead ll; RV₄=R wave amplitude recorded in precardial lead V₄.

Abbreviations: A. Fib.=atrial fibrillation; BW=body weight in pounds; HR=heart rate; L. Axis Deviation=left axis deviation (frontal plane mean electrical axis [MEA] ranging from +30.0^o counterclockwise to -90.0^o, usually indicative of either left ventricular enlargement or the result of a conduction abnormality affecting the left ventricle); LVH pattern=left ventricular hypertrophy pattern (this diagnosis is usually based on a finding of increase in R-wave amplitude in Lead II [i.e., >3.0 mV] or Lead V₄ [>3.8 mV], which supports a diagnosis of left ventricular hypertrophy); 1^st Degree AV Block=suggests a mild form of atrioventricular block characterized by a prolongation of the P-R interval in the scalar EGG; Q-T Int. Prolongation by definition is a prolongation of the combined ventricular repolarization processes (i.e., T wave), which has been shown in man to be a predisposing factor in the development of ventricular arrhythmias; R. Axis deviation=right axis deviation (frontal plane MEA ranging from +100.0^o clockwise to -90.0^o, usually suggestive of right ventricular enlargement or of a conduction abnormality involving the right ventricle); Right B.B. Block=right bundle branch block (this finding suggests complete interruption of the major conduction pathway to the right ventricle); SVP Beats=supraventricular premature beats (these are abnormal beats which occur earlier than expected and arise from the atria or upper chambers of the heart); and Vent. P Beats=ventricular premature beats (these are abnormal beats which arise from a focus in the ventricle and occur earlier than the normal cardiac pacemaker).