Sick Sinus Syndrome (SSS) in Dogs

Sick Sinus Syndrome (SSS) in Dogs

Sick Sinus Syndrome (SSS) is a condition where the sinus node (normal pacemaker of the heart) is diseased and not responding normally to the body’s needs.  

This disease is often a result of fibrosis/scarring of the sinus node or surrounding tissue, which prevents the signals from forming or being conducted.  

Affected patients can range in severity from mild (no clinical signs) to severe (collapse, lethargy, weakness – especially with excitement).  Often, the sinus node stops suddenly and a long pause occurs, followed by a ventricular escape beat.  

This condition carries the risk of sudden death.  

Medications may be attempted to increase the sinus rate; however, these are often ineffective or only effective in the short-term.  A permanent pacemaker is usually required to ensure the heart rate does not drop below the minimum programmed rate.

3rd Degree Atrioventricular (AV) Block in Dogs

3rd Degree Atrioventricular (AV) Block in Dogs

3rd Degree Atrioventricular (AV) Block is a condition where the signals for the heart rate from the sinus node are not received or allowed through the AV Node.  

This is usually a result of scarring/fibrosis of the AV Node where the conductive tissue is no longer allowing the signals to travel through this region.  

This results in a rhythm called a ventricular escape rhythm that is enough to keep the patient alive, but is very slow (typically 30-40 beats per minute).  Affected patients often collapse and have extreme exercise intolerance because their heart rates are not appropriate for higher activity levels.  

This condition is typically incurable; however, this can be treated with a pacemaker, which ensures the heart rate never drops below the minimum programmed value.  

Until a pacemaker can be implanted, medications can be attempted to increase the ventricular rate slightly.  

These medications are typically effective for only a short time, if at all.

2nd Degree Atrioventricular (AV) Block in Dogs

2nd Degree Atrioventricular (AV) Block in Dogs

2nd Degree Atrioventricular (AV) Block is a condition where the AV Node allows only some sinus-initiated beats to travel through the node into the ventricle, while others are blocked.  

This can range in severity from mild (occasional blocked beats) to severe (High-Grade 2nd Degree AV Block).  

The mild forms are often a result of higher vagal (parasympathetic) tone and rarely if ever cause clinical signs.  

Commonly, this is associated with intracranial (neurologic), gastrointestinal, respiratory, bladder, or ocular disease.  

An atropine response test will differentiate vagal from primary nodal causes.  Mildly affected patients should be monitored for any evidence of progression.  

The severe forms (High-Grade 2nd Degree AV Block) can result in collapse, weakness, exercise intolerance, and lethargy.

This condition is almost always due to a fibrosis/scarring of the AV Node that prevents signals from conducting through appropriately.  

In severe cases, a permanent pacemaker is required to ensure the heart rate does not drop below the minimum programmed heart rate.

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) in Dogs

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) in Dogs

Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC) is a condition that most frequently occurs in boxer dogs.  

This condition consists of the right ventricle being infiltrated with a fatty or fibrofatty tissue that destroys the normal myocardium.  

This leads to the development of severe ventricular arrhythmias (VPCs and Ventricular Tachycardia) that can be life-threatening.

While there is no cure for this disease, antiarrhythmic therapy is utilized to attempt to reduce the risk of sudden death.  

It is typically impossible to eliminate all arrhythmias and sudden death remains a possibility regardless of therapy.  

24 hour Holter Monitor examinations are the best possible way to evaluate the arrhythmia frequency and grade.  

With this information, we can further direct antiarrhythmic therapy.

Ventricular Premature Complexes in Dogs

Ventricular Premature Complexes in Dogs

Ventricular Premature Complexes or Ventricular Tachycardia is an electrical disturbance, where the ventricular myocardium depolarizes at incorrect times.

These may be due to numerous etiologies, which include; cardiac disease, pericardial effusion, metabolic disease and electrolyte disturbances, tickborne disease, fever, pain, anemia, altered autonomic tone, trauma, sepsis, DIC, gastric dilatation with/without volvulus, splenic disease, hepatic disease, gastrointestinal disease, and pheochromocytoma.  

The primary risk with this condition is an R-on-T phenomenon that can cause 

ventricular fibrillation and sudden death.  Antiarrhythmic therapy is utilized in certain cases to reduce the frequency of these abnormal beats.

Addressing the underlying condition is the best possible strategy; however, this still may not eliminate all abnormal activity.  

Follow up electrocardiograms and 24 hour Holter Monitor examinations are necessary for patients with this arrhythmia to continue to optimize medical therapy.

Atrial Premature Complexes in Dogs

Atrial Premature Complexes in Dogs

Atrial premature complexes are often the result of atrial dilation (left or right); however, additional considerations would be mechanical irritation (perihilar lymph node enlargement, atrial/auricular mass, heart base tumor, pericardial disease, etc.), infectious/tick-borne disease, metabolic disturbances, or potentially altered autonomic tone (sympathetic/parasympathetic imbalance).  

This rhythm is fortunately not considered fatal in itself.  

If atrial dilation is the underlying etiology, your pet may go into atrial fibrillation in the future.  Antiarrhythmic therapy may be indicated based on the frequency and grade of atrial arrhythmias noted on the ECG.

Atrial Fibrillation in Dogs

Atrial Fibrillation in Dogs

Atrial fibrillation is a condition where the atrium (top chambers of the heart) are no longer allowing organized electrical activity.  

Rather, there is a random oscillation of electrical waves that do not allow the atrium to contract as they should.

 The Atrioventricular Node (AV Node) responds to this haphazard electrical activity in a very irregular and rapid pattern, causing a very irregular, rapid heart (pulse or ventricular response) rate.  

This condition is typically the result of severely dilated chambers.  

This condition can rarely be corrected; however, the ventricular response rate can be lowered to a reasonable level with medications, frequently the combination of Digoxin and Diltiazem.

Continued rechecks and monitoring for adequate heart rate control are essential to ensure these patients remain at an optimal heart rate and do not develop congestive heart failure (fluid in the lungs).

Ventricular Septal Defect (VSD) in Dogs

Ventricular Septal Defect (VSD) in Dogs

A Ventricular Septal Defect (VSD) is a congenital cardiac disease, causing communication between the left and right ventricle.  

These can occur in numerous locations and the changes to be expected depends on the exact location.  

The development of left-sided (most common in veterinary medicine) or right-sided congestive heart failure is possible.  

Based on the precise findings, we will discuss appropriate management options.  Some cases require monitoring, others medical management, and some surgical intervention.

Congenital Mitral Valve Dysplasia in Dogs

Congenital Mitral Valve Dysplasia in Dogs

Congenital Mitral Valve Dysplasia is a condition where the mitral valve (separating the left atrium and left ventricle) did not form correctly at birth.  As a result, the valve does not close (coapt) normally.

This poor coaptation allows reverse blood flow (left ventricle into left atrium), which is termed regurgitation or insufficiency.  

This disease is progressive in that the chambers will continue to dilate, but the valve structure likely will not change.  

Routine rechecks are required to monitor for any changes to the left atrium or ventricle that may warrant additional testing or direct medical management of this disease.  

Eventually, this disease can lead to the development of congestive heart failure (fluid in the lungs), which is a medical emergency that makes breathing very difficult.

Tricuspid Valve Dysplasia in Dogs

Tricuspid Valve Dysplasia in Dogs

Tricuspid Valve Dysplasia is a congenital disease where the tricuspid valve did not form properly in utero.  

This condition allows tricuspid regurgitation (backwards blood flow) which causes a volume overload to the right heart.  

The long-term prognosis is difficult to predict, but often favorable.  Life-long medications and recheck appointments are often necessary.  

Affected patients may eventually progress into right-sided congestive heart failure.  

Clinical signs of right-sided congestive heart failure may include abdominal swelling (ascites) and/or pleural effusion (fluid inside the chest, around the lungs).  

This may make breathing difficult and additional therapy will be required.

Pulmonic Valvular Stenosis in Dogs

Pulmonic Valvular Stenosis in Dogs

Pulmonic valvular stenosis is a congenital condition wherein the valve did not form properly in utero.

This valve does not open completely and makes the right ventricle work very hard to eject the blood volume.  

Over time, this causes severe hypertrophy (thickening) of the right ventricle. Medications may help reduce this severe gradient.  The recommended surgery for severe disease is a pulmonic 

stenosis balloon valvuloplasty to open the abnormal valve.  

This is an endovascular surgery, where a small incision is made over the jugular vein and the balloon is passed through the blood vessels to the pulmonic valve.  

The goal of this procedure is to reduce the pressure gradient by 50% or more. As long as dogs are within the mild to moderate categories (less than 80mmHg), their quality of life and life expectancy is typically good to excellent.  

Without surgery, patients with severe disease may eventually go into right sided congestive heart failure (fluid accumulation in the belly or thoracic cavity), develop life-threatening arrhythmias, or display weakness or collapse.

In some cases, the pulmonic valve annulus is also reduced (annular hypoplasia), which complicates or limits surgical options.  

In severe cases, it may preclude a surgical option and we must manage these patients with medications alone.

In some breeds, an abnormal right coronary artery (R2A anomaly) can be present, which may make surgery difficult or potentially impossible.  

An angiogram (contrast injected into the blood vessels) is necessary to investigate this prior to the valvuloplasty being performed.

Equivocal Subaortic Stenosis in Dogs

Equivocal Subaortic Stenosis in Dogs

Equivocal Subaortic Stenosis is a “grey zone” where we cannot tell if the patient has mild disease (affected) or no disease.  

When patients are beyond one year of age, this is highly unlikely to progress or change.  

Recheck echocardiograms beyond two years of age may be helpful to determine if there is progression, but often no follow up is required.

Subaortic Stenosis in Dogs

Subaortic Stenosis in Dogs

Subaortic Stenosis is a condition where the aortic outflow tract is narrowed.  

Most frequently, this a result of a partially or fully encircling fibrous ring just below the aortic valve.  

This can make it very difficult for blood to exit the left ventricle, causing marked elevation in left ventricular pressures.

In moderate to severe cases, this will then cause severe left ventricular hypertrophy (thickening).  This disease is “fixed” (non-progressive) after 1 year of age.  

Patients with this condition (even mild) are at increased risk for infective endocarditis (infection of the heart valves).  

Any suspicion of infection (urinary tract, respiratory, tooth root abscess, skin infection, etc.) should be immediately diagnosed and treated based on the results of a culture and sensitivity profile.  With severe disease, these 

patients may develop ventricular arrhythmias and may have a higher incidence of sudden death.

Recheck physical examinations and electrocardiograms (ECGs) are recommended to monitor for any abnormal electrical activity that may require treatment.

Reverse Patent Ductus Arteriosus (rPDA) in Dogs

Reverse Patent Ductus Arteriosus (rPDA) in Dogs

A right to left Patent Ductus Arteriosus (Reversed PDA or rPDA) is a congenital defect where the ductus arteriosus (fetal vascular connection) remains present after birth.  

The pulmonary pressures rise dramatically due to a problem within the lungs (Eisenmenger’s Physiology), causing blood to flow from the main pulmonary artery into the descending aorta.  

This high concentration of deoxygenated blood causes a high degree of deoxygenated blood to flow to the back half of the body, particularly the kidneys.  

This is seen clinically as differential cyanosis (blue/purple caudal membranes, pink cranial membranes).  A rPDA results in severe elevations of the hematocrit (PCV or HCT) as the kidneys respond to the deoxygenated blood by signaling for more red blood cell production.  

Affected patients will typically become neurologic (seizures, altered mentation, weakness, collapse, inappetance, or trembling) as the hematocrit rises.  

These patients are also at risk for sudden death due to arrhythmias, neurologic conditions (embolic events or seizures), or potentially right-sided congestive heart failure.

There is no cure for this condition.  Therapy is directed towards lowering the pulmonary pressures, thus reducing the degree of shunting and therapeutic phlebotomy (blood draws) as necessary to maintain the hematocrit around 60-65%.  

The prognosis is typically poor; however, some patients will live for many years with optimal medical management.

Patent Ductus Arteriosus (PDA) in Dogs

Patent Ductus Arteriosus (PDA) in Dogs

A Patent Ductus Arteriosus (PDA) is a congenital defect where the ductus arteriosus (fetal vascular connection) remains patent after birth.  

This allows blood to flow from the aorta into the main pulmonary artery.  

If left untreated, this allows severe fluid overload to the left side of the heart.  This causes severe left atrial and left ventricular dilation, eventually resulting in left-sided congestive heart failure (fluid on the lungs).  

Affected patients will typically progress into congestive heart failure by 1 year of age and most patients will die by 3 years of age.  

It is important to monitor these patients for the development of congestive heart failure as medications are required to control this condition and maximize life expectancy and quality of life.

Fortunately, with surgical correction, the life expectancy of patients with this condition is generally normal (unless advanced myocardial insult has happened before diagnosis).  

The surgical procedure typically recommended is a transvenous occlusion, but the size of your pet may impact surgical options.  

This is a minimally invasive surgery that is performed through a small incision in the rear limb.  

The catheter is passed across the PDA from the femoral artery and a device (coil, plug, or occluder) is placed within the PDA.  

This allows a blot clot to form that is eventually replaced with fibrous tissue, resulting in a permanent occlusion.

Physiologic Murmur in Dogs

Physiologic Murmur in Dogs

A physiologic murmur is common in large-breed dogs.  

This represents mild turbulence within the great vessels and is not the result of structural heart disease.  

No treatments or medications are required.

Pulmonary Arterial Hypertension in Dogs

Pulmonary Arterial Hypertension in Dogs

Pulmonary arterial hypertension is a state of high blood pressure within the lung (pulmonary) circulation.  

This condition can be due to heartworm disease and embolic disease (clots into the lungs); however, some cases are considered idiopathic (cause unknown).  

Many cases may also develop pulmonary arterial hypertension due to chronic airway disease (pulmonary fibrosis, cancer, or pneumonia).  

This disease process involves damage to the pulmonary arteries and thickening/constriction of these vessels, increasing resistance to flow.  

Medications are utilized to reduce the pulmonary arterial pressures and improve quality of life.  

No medications can return these pressures to normal; however, many patients display a significant improvement in their quality of life.

Systemic Hypertension in Dogs

Systemic Hypertension in Dogs

Systemic Hypertension is a state of high blood pressure within the body.

This means that the heart must work very hard to propel blood forward, which increases oxygen demands and can cause changes to the myocytes (muscle cells).  

In veterinary medicine, this condition is typically a result of chronic kidney disease, thyroid disease, or various other metabolic conditions.  In some cases, essential (idiopathic) hypertension may be suspected.  

This condition can cause severe end-organ damage to include the brain, heart, kidneys, and eyes.  

If an underlying condition can be identified, treatment is directed towards that condition and maintaining the systemic blood pressure at a reasonable level with medications.  

Frequent rechecks are required to optimize the dose of anti-hypertensive medications.

Heart Base Tumors in Dogs

Heart Base Tumors in Dogs

Heart Base Tumors are most frequently chemodectomas, which are benign, slow growing tumors of the aortic body chemoreceptors.  

These tumors can cause the accumulation of fluid within the pericardial sac (pericardial effusion), which can eventually be enough to cause cardiac tamponade (collapse of the chambers of the heart).  

This condition is typically best managed by surgical removal of the pericardium (pericardial window or subtotal pericardectomy) as the rate of fluid accumulation is typically very slow.  

These tumors are poorly responsive to chemotherapy and radiation given their very slow growth patterns.  

Recheck echocardiograms are warranted to monitor for any changes that may suggest a different tumor type, such as a carcinoma.

Right Auricular Mass in Dogs

Right Auricular Mass in Dogs

A right atrial/auricular mass is most likely a hemangiosarcoma.  

Other tumor types would include chemodectoma or carcinoma.  

The prognosis is typically poor; however, with chemotherapy and surgery (pericardectomy or pericardial window), these patients can typically have a high quality of life.

Their overall life expectancy is unfortunately short (typically 90-120 days).  Consultation with an oncologist is highly recommended to discuss potential treatment strategies and the associated survival times and quality of life with each potential chemotherapeutic option

Pericardial Effusion in Dogs

Pericardial Effusion in Dogs

Pericardial Effusion is a condition where there is a fluid accumulation within the pericardial sac.  

This causes the pressures outside of the heart to rise.  

When a critical pressure is reached, the chambers of the heart begin to collapse, a condition called tamponade.  

This is a life-threatening emergency and requires immediate medical attention as death will occur shortly after the development of tamponade.  

The fluid is often due to a tumor located in the heart base or right auricular region.

Recheck echocardiograms are necessary as some masses that bleed are very small and cannot be identified during the initial examination.

Surgical procedures such as a pericardial window or subtotal pericardectomy (removal of the sac) can prevent tamponade from returning; however, there is a risk of uncontrolled hemorrhage with these procedures.

A pericardiocentesis is a procedure where a needle is inserted into the pericardial sac and the fluid is removed.  This fluid is submitted for cytologic review

Dilated Cardiomyopathy in Dogs

Dilated Cardiomyopathy in Dogs

Dilated Cardiomyopathy is a primary myocardial disease wherein the heart muscle is damaged and becomes very weak.  

The left ventricle dilates and has a marked systolic dysfunction (pump dysfunction).  

This causes an elevation in left ventricular and left atrial pressures as the poorly pumping chamber continues to dilate.  

Eventually, this results in dilation of the left atrium and fluid accumulation within the lungs (congestive heart failure).  

This makes breathing difficult and requires urgent medical attention.

Unfortunately, there is no cure for this disease.  

Ongoing rechecks and medical management are utilized to maximize the quality of life for affected patients.  

The disease progression is variable, with some patients doing well for years and others progressing into congestive heart failure rapidly.  

This disease is also frequently associated with the development of arrhythmias (abnormal electrical beats) that can predispose affected patients to sudden death.

Additional diagnostics, such as 24 hour Holter Monitors, may be recommended based on our initial findings.  

If any clinical signs of arrhythmias such as a “dazed” appearance or collapse are noted, please contact your trusted veterinarian or your local emergency clinic immediately.

Chronic Valve Disease in Dogs

Chronic Valve Disease in Dogs

Myxomatous Mitral Valve Degeneration (i.e. Chronic Valve Disease or Endocardiosis) is a chronic, degenerative disease of the mitral valve (62% of affected patients have only mitral valve changes).

The normally thin and delicate valve leaflets are damaged and the tissue replaced with a thickened, non-pliable tissue.  

This causes the valve leaflets to become thickened, irregular, and have poor coaptation (closure).  

This poor coaptation allows reverse blood flow (left ventricle into left atrium), which is termed regurgitation or insufficiency.  

This disease is progressive and unfortunately, there is no cure.  

Routine rechecks are required to monitor for any changes to the left atrium or ventricle that may warrant additional testing or direct medical management of this disease.  

Eventually, this disease can lead to the development of congestive heart failure (fluid in the lungs), which is a medical emergency that makes breathing very difficult.  

This disease can also affect the tricuspid valve (right side of the heart) and cause similar problems.  

One study indicates 32.5% of cases have concurrent mitral and tricuspid valve degeneration.  This study indicated 1.3% of affected patients have only tricuspid valve changes.

Congestive Heart Failure in Dogs

Congestive Heart Failure in Dogs

Left-Sided congestive heart failure occurs when the pressure in the blood vessels in the lungs increases causing fluid to leak from the vessels into the surrounding lung tissue.  

Right-Sided congestive heart failure is a similar process where the fluid accumulates within the pleural space (around the lungs) or the abdomen (ascites).  

This condition makes it difficult to exchange oxygen causing difficulty breathing, increased respiratory rate or effort, coughing, cyanosis (blue color to gums or tongue), and/or weakness and/or collapse with exertion.  

Congestive heart failure in dogs is a life threatening condition and your pet should be evaluated as soon as signs are noted, which may require an emergency hospital visitation.