The Irish Wolfhound Foundation

Cardiac Lessons from the Lifetime Cardiac Study Data

Posted Jun 01, 2016 - written by Mariellen Dentino MD.

In 1986 a group of breeders invited Dr. Serena Brownlie to record EKGs on Irish Wolfhounds at shows and at kennels in the United Kingdom. She found an overall 11% incidence of atrial fibrillation in the tested population and a very high prevalence of other electrocardiographic abnormalities.

In 1992 Phillipa Crowe helped Dr Neil Harpster begin EKG testing of American hounds at the National Specialty.

A total of 821 Ekgs were done at the National from 1992-2000. The population tested was asymptomatic hounds traveling to the National and overall 8.9% of these hounds were in atrial fibrillation with 22% having
some abnormality on their EKG.

There was a striking rise in the incidence of afib with increasing age. Only 3.9% of hounds 2-3 years (often breeding age) were in afib and only 17% had any EKG abnormality. In the 7 year old hounds 29.2% were in afib and 50% had some abnormality on their EKG.

In humans many of these EKG abnormalities have clinical significance but their importance was unknown in Iws. Thus many EKG abnormalities were identified in the hounds but there was no advice to offer owners and breeders.

Lifetime Cardiac Study

In 2000 enrollment for the Irish Wolfhound Lifetime Cardiac Study opened. The Framingham Study which had enrolled citizens of a small NE community and followed them for their lifetime was providing new insights on cardiovascular disease for humans at an astonishing rate and it was hoped this could be accomplished for Irish Wolfhounds.

Owners were asked to complete an entry questionnaire and EKG and to provide a yearly EKG and report for each entered hound. Entry closed with 1242 entries. Unfortunately the questionnaire was lengthy and many hounds had “gap years” in their data. There was at least intermittent follow up and cause/date of death data available for 819 hounds.

Prognosis of EKG Abnormalities in Irish Wolfhounds

There are many EKG abnormalities of conduction (a quirk in the way the beat travels through the heart). Hounds with these abnormalities were followed through their lifetime and did not develop cardiomyopathy or have a shorter life span. The only non-arrhythmia EKG abnormality that led to cardiac disease was AVBlock. Hounds with this abnormality were more likely to develop atrial fibrillation.

OF ALL THE ABNORMALITIES SEEN ON EKGS ONLY ARRHYTHMIAS WERE PREDICTORS OF ANY CARDIAC DISEASE AND ONLY ATRIAL FIBRILLATION PREDICTED IW CARDIOMYOPATHY.

Arrhythmias of Concern

VPCs are beats that occur early and originate in the pumping chamber of the heart. This is a sporadic  arrhythmia and thus the incidence is uncertain. In screening studies they have been reported to occur in 2.6-4.8% of asymptomatic Iws. In Boxer/Doberman they are associated with progressive DCM and sudden death. In the IW (when they are the only rhythm abnormality) they are not associated with progressive cardiomyopathy. However the incidence in sudden death in hounds with VPCs is twice that of the overall population. Please see the Summer 2015 Focus for in depth report of VPCs. (Past issues can be viewed on the IWF web site).

APCs are beats that occur early and originate in the top part of the heart (atria). These are also intermittent and the incidence is not known. Fifty eight percent of hounds with these beats on an EKG progressed to atrial fibrillation and in both the English and our population they are felt to be precursors to atrial fibrillation.

The most important arrhythmia in the IW is atrial fibrillation. This is the only EKG abnormality that leads to IW cardiomyopathy. Normally the heart beat begins in the atria or top part of the heart and progresses to the ventricle or pumping chamber of the heart in an orderly manner. In atrial fibrillation the beats from the top part of the heart are sporadic and often very fast with not all of the beats reaching the ventricle to cause contraction of the pumping chambers. If the rate of the abnormal beats in the atria is slow the hound may tolerate this well although the overall efficiency of the cardiac output is decreased. In the LCS population of 819 IWs 164 or 20.02% were affected with atrial fibrillation.

Characteristics of hounds with Afib

In the LCS data the mean age of onset of afib in males was 5.14 years and females 5.64 years- usually after breeding age.

61.7% had a known close relative with afib.

55.3% were on treatment for their cardiac disease.

All hounds with afib need rate control. Dr Jan Bright (Colorado State University) using LCS study hounds showed the heart rate at the study site and at home (using 24 hour holter monitoring) did not correlate thus making it important for owners of afib hounds to monitor heart rates.

As cardiomyopathy progresses other meds are helpful.

42.6% of hounds with afib died of cardiomyopathy thus about 10% of hounds overall die of cardiomyopathy.

Mean survival time after the diagnosis of afib in the males was 2.64 years- but the range was 1-6 years. Mean survival for bitches after diagnosis of afib was 2.80 years with range 1-7 years. 

Over half (57.4%) of hounds diagnosed with afib died of non cardiac related ailments.

The mean survival time for these hounds after the diagnosis of afib was 2.33 years (range 1-8 years). Most of the hounds dying less than 2 years after the diagnosis of afib were 7 or older when the diagnosis of afib was made. Certainly the afib may have played a role in the non cardiac deaths, ie: surgery complications for bloat, decreased stamina, and muscle strength in rear weakness. However the diagnosis of afib did not condemn all hounds to a death from progressive cardiomyopathy.

Note that the hounds with atrial fibrillation actually live longer than the population with normal EKGS. 

Eighty percent of hounds were euthanized and this may help to explain the difference in life span.

The trigger for euthanasia may be different for hounds with cardiomyopathy. Medications are effective, well tolerated, and usually affordable. Hounds with normal EKGs die mainly from cancer and fear of poorly tolerated treatments and pain for the hound may trigger earlier euthanasia.

Atrial fibrillation and cardiomyopathy do not result in a reduced life span for the IW.

EKG /Echo Screening in Asymptomatic North American Irish Wolfhounds

After years of following IW EKGs we had seen very few hounds with symptomatic heart disease without previous atrial fibrillation. In most giant breeds dilated cardiomyopathy develops and afib comes later. This did not seem to be the case in the IW.

To determine if the EKG (less expensive and more easily available) was an adequate screening test for heart disease in the IW 576 different hounds were screened with simultaneous EKG and Echocardiogram.

Remember the EKG will diagnose rhythm problems but an echo is needed to see if the chambers of the heart are enlarged or weakened or if heart valves are malfunctioning. This study included hounds brought to the National or Regional Specialties and was sponsored by the IWF.

After official publication a more detailed summary of this important data will be in Focus.

IW cardiomyopathy begins with atrial fibrillation and then progresses to enlargement of the left atria and then the left ventricle. The left ventricle initially retains fairly preserved pumping performance- unlike the usual Dane/ Doberman dilated cardiomyopathy.

In the hounds evaluated in this study only one had the usual giant breed heart disease and had an abnormal echo without atrial fibrillation. We do have outside data of two other such hounds- so it does occur- but is very infrequent.

Atrial fibrillation as a predictor of IW cardiomyopathy showed a sensitivity of 98.7% (low false negatives) and a specificity of 97.05% (low false positives). Thus in the IW an EKG is an adequate screening test for IW Cardiomyopathy. Very few hounds will have cardiomyopathy with a normal EKG.

Insufficient closing of the mitral valve is very common in hounds with atrial fibrillation. Non pathological valve abnormalities are very common in normal hounds. Significant valve disease was infrequent but was found in a small number of hounds.

Summary

Although the population screened was small, results of the EKG/ECHO study showed the EKG to be an adequate screening test for IW cardiomyopathy. Because of the increase in atrial fibrillation with age the EKG needs to be done yearly. If the EKG is normal an echo is not needed to diagnose occult DCM in the Irish Wolfhound.

IW cardiomyopathy is not the same as the DCM in most large/giant breeds.

There were some hounds with clinically significant valve abnormalities and hounds need at least one auscultation by a cardiologist and an echo if a non trivial murmur is heard.

One in four north american IWs has some abnormality on screening EKG. Of all these abnormalities only the arrhythmias were of concern.

Atrial fibrillation is the only arrhythmia that predicts IW cardiomyopathy.

There was a 20% overall incidence of atrial fib in the LCS study.

The average age of onset of atrial fib is 5 years.

Hounds with atrial fib do not have shortened life span.

Only half of these afib dogs die of cardiac disease, living 1-8 years after diagnosis.

The incidence of death from cardiac disease has decreased in the last 10 years.

There is a male preponderance of cardiac death which is most marked in young hounds.

More than 60% of hounds with atrial fib have a known close relative with afib. Thought to be a autosomal dominant trait with varied expression and modifiers.

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