Cutting Edge Cardiology: Five State-of-the-Art Developments

Ashley B. Saunders, DVM, Diplomate ACVIM (Cardiology), Texas A&M University

Making a difference in the diagnosis and management of dogs and cats with heart disease—Dr. Saunders highlights 5 developments in veterinary cardiology: Digital radiography, cardiac biomarkers, smartphone apps and devices, cardiac medication, and interventional procedures.

Veterinary practitioners strive to provide patients and owners with state-of-the-art preventive, diagnostic, and therapeutic care. This article highlights 5 developments in veterinary cardiology that have made a difference in the diagnosis and management of dogs and cats with heart disease. These developments encompass:

• Diagnostic tests
• Technology
• Cardiac medications
• Other cardiac therapies.

1. DIGITAL RADIOGRAPHY

Digital radiography is now used in many veterinary practices, and thoracic radiographs are an integral part of a cardiac evaluation. Improvements in technology and image quality produce radiographic images that are undoubtedly helpful in:

• Diagnosing and monitoring cardiac disease and congestive heart failure (CHF)
• Identifying noncardiac causes of cough (eg, mainstem bronchial compression, tracheal collapse, inflammatory airway disease).

The benefits of current digital technology include:

• Rapid acquisition of images and ability to make contrast adjustments that improve image quality without having to change settings and retake images, as required when using standard film.
• Post processing software that allows the clinician to zoom in on specific structures of interest or take measurements (Figure 1). For example, vertebral heart size measurement establishes baseline heart size and can be used to trend patient data.
• Digital files of radiographic images that can be stored, retrieved, and transmitted immediately to colleagues, clients, or specialists. The ability to rapidly share digital images allows practitioners and specialists to work together seamlessly, enhancing patient care.

2. CARDIAC BIOMARKERS

A biomarker is a measure of a biological or pathologic process that can be used to:

• Detect disease
• Monitor disease progression
• Potentially determine treatment approach
• Predict prognosis.

Cardiac biomarker measurement is not a stand-alone test, but rather part of a diagnostic evaluation that includes thoracic radiographs, electrocardiography, and echocardiography; these collective diagnostics determine the clinical picture for each patient. Numerous studies in dogs and cats have been performed over the past decade to determine which cardiac biomarkers are most useful, and how best to interpret measurement results.

Cardiac Troponin I

The serum level of cardiac troponin I, a protein involved in cardiac muscle contraction, is a sensitive and specific marker of myocardial damage. High-sensitivity cardiac troponin I assays (ADVIA Centaur TnI-Ultra Assay, medical.siemens.com; validated and available at vetmed .tamu.edu/gilab/service/assays/cardiac-troponin) have a lower detection limit than standard assays, which allows the former to detect lower circulating levels of cardiac troponin I. Elevations denote myocardial injury but do not indicate the specific cause of the damage, similar to alanine aminotransferase as a blood-based indicator of hepatic cellular damage.

Some cardiac troponin I release from myocardial cells occurs with age, often resulting in measurable concentrations. Significant elevations can indicate:

• Isolated insult or continuous myocardial damage, depending on whether values decrease or remain persistently elevated
• Myocarditis caused by infectious or parasitic agents, such as Chagas’ disease
• Noncardiac diseases, including gastric dilation volvulus and sepsis (eg, pyometra).

N-Terminal Pro–B-Type Natriuretic Peptide

Natriuretic peptides are released in response to stretch or damage to the heart, and are elevated in the most commonly diagnosed acquired (versus congenital) heart diseases (Table 1). In dogs and cats, specific indications for measuring N-terminal pro–B-type natriuretic peptide (NT-proBNP) include:²

• Detection of heart disease in suspect animals of predisposed breeds or families
• Presence of physical examination findings or clinical signs of heart disease
• Differentiation of respiratory from cardiac causes of breathing difficulty.

As noted in the last bullet, elevations in NT-proBNP can increase veterinary practitioners’ confidence in distinguishing heart failure from respiratory disease in cats with respiratory signs.³

More recent data suggests that elevated NT-proBNP values in Doberman pinschers indicate additional testing with echocardiography to aid in detection of occult dilated cardiomyopathy (DCM).⁴ This is of particular interest because occult DCM can be challenging to identify and, if therapy is initiated early in the disease process, patients may experience significantly extended time to clinical signs and survival.

3. SMARTPHONE APPS & DEVICES

Technological advances have allowed smartphones to be valuable tools in the diagnosis and monitoring of heart disease.

AliveCor Products

The AliveCor heart monitor device (alivecorvet.com), which is compatible with the iPhone 4/4S/5/5S/5C, wirelessly communicates with the free, downloadable Veterinary AliveECG app that provides instant, high-quality electrocardiograms (ECGs) and heart rate data in dogs, cats, and other species (Figure 2).

The device can be attached to the phone as a case, or used in proximity to the phone, which can be particularly useful for anxious, panting, or small pets. The ECG is recorded as a rhythm strip, with the ability to annotate with patient information as well as adjust recording speed, duration, and sensitivity settings. ECGs can be saved, stored, and transmitted as PDF files.

Resting Respiratory Rate App

Involving owners in monitoring their pets’ heart disease can promote successful patient management and improve quality of life. The Resting Respiratory Rate app (yourdogsheart.com) for both iPhone and Android smartphones provides a mechanism for owners to record resting respiratory rate (RRR) and allows the data to be transmitted from owner to veterinarian.

Once an owner is properly instructed and a normal at-home respiratory rate for the pet is determined, respiratory rates acquired at home, while the pet is resting or sleeping, can be incredibly useful when monitoring CHF. For example, most dogs have a RRR less than 35 breaths/min, and many dogs have rates that are much lower—in the mid-teens to mid-twenties. Owners who report clinical signs of heart failure (Table 2) can be advised to administer additional diuretic therapy and seek medical attention. It can be used in cats with heart disease as well.

4. CARDIAC MEDICATION

Pimobendan (VETMEDIN, vetmedin.com) is a phosphodiesterase-3 inhibitor and calcium sensitizer classified pharmacologically as an inodilator because it exerts combined positive inotropic and vasodilatory effects. Pimobendan:

• Has proven efficacy in managing heart failure in dogs with DCM5 and degenerative mitral valve disease (DMVD)⁶
• Is currently recommended as standard of care for managing heart failure in dogs, along with furosemide and an angiotensin-converting enzyme (ACE) inhibitor.

Degenerative Mitral Valve Disease

In DMVD, pimobendan significantly improved survival by a median of 267 days (approximately 8.9 months) in dogs with heart failure.⁶

In 2009, the American College of Veterinary Internal Medicine published guidelines for the diagnosis and treatment of DMVD that advocate the use of pimobendan in stages C (past or present signs of heart failure) and D (refractory or end-stage heart failure).⁷ This consensus statement and associated staging system provide veterinary practitioners with the tools to diagnose, stage, and schedule recheck evaluations that help owners manage their dogs’ heart disease.

The use of pimobendan in preclinical DMVD is currently being investigated.

Dilated Cardiomyopathy

The benefits of pimobendan, and indications for its use, continue to expand as the results of clinical trials are published. In preclinical DCM in Doberman pinschers, pimobendan prolonged the time to onset of clinical signs of CHF or sudden death and extended survival compared with placebo.⁸

Other Cardiac Diseases

Pimobendan may be included in the management of heart failure in dogs with other diseases, most notably pulmonary hypertension and congenital heart disease, such as patent ductus arteriosus (PDA).

Retrospective evaluation suggests pimobendan appears to be safe and well tolerated in cats with heart failure and cardiomyopathy,^{9, 10} especially when characterized by systolic dysfunction.⁹ Prospective evaluation is currently in progress.

5. INTERVENTIONAL CARDIOLOGY

Interventional procedures use minimally invasive techniques in the diagnosis and treatment of congenital and acquired cardiovascular disease. The number and type of procedures performed in veterinary medicine continue to expand and increase.

Pet owners have become familiar with minimally invasive options for themselves and, when appropriate and if given the option to have surgery or a catheter-based procedure, many prefer a minimally invasive procedure for their pets to avoid the incisions and recovery time associated with surgery.

Patent Ductus Arteriosus

Catheter-based procedures are a well-established treatment option for occluding PDA, one of the most common congenital heart diseases in dogs. Without ductal closure, most dogs with a PDA have a shortened life span and develop signs of left heart failure in the first year of diagnosis. Therefore, the diagnosis and closure of a PDA is important with regard to maintaining a dog’s long-term health.

Minimally invasive closure of a PDA is made with an appropriately sized device, such as an embolization coil, Amplatzer vascular plug, or Amplatz canine ductal occluder (ACDO) (infinitimedical.com), typically via the right femoral artery. The ACDO is the first device developed specifically for dogs (Figure 3), and is a preferred method of PDA closure, resulting in shorter procedure times and higher ductal closure rates compared to other devices.¹¹

Surgical ligation via thoracotomy is recommended for:

• Small dogs weighing less than 2.5 kg, due to issues with vascular access
• If the anatomy of the PDA is not amenable to device closure.

Figure 3. Images obtained with fluoroscopy in a dog with a patent ductus arteriosus (PDA). An angiogram was performed with contrast through a catheter in the descending aorta to confirm location and anatomy of the PDA (A). A second injection followed the deployment and release of an Amplatz canine ductal occluder to document complete occlusion of the PDA (B). A measuring catheter is present in the esophagus in both images.

Other Cardiac Conditions

Interventional vascular procedures are also available for:

• Occlusion of atrial and ventricular septal defects, portosystemic shunts, and arteriovenous malformations in various locations
• Balloon valvuloplasty of pulmonic valve stenosis, cor triatriatum, and subaortic stenosis
• Heartworm extraction through the jugular vein for dogs, cats, and ferrets with heartworm disease and high heartworm burdens, especially if caval syndrome or hemolysis is present.

Interventional procedures are performed by specialists with appropriate training, and require specialized equipment, including fluoroscopy, a range of catheters, wires and devices, and imaging capabilities. Contact a local cardiologist for additional information regarding therapeutic options, cost, and prognosis.

SUMMARY

• Digital radiography has enhanced the ability to acquire, store, and transmit thoracic radiographic images, and is a valuable diagnostic tool when performing a cardiac evaluation.
• Biomarker results are a component of a diagnostic evaluation, and additional testing (eg, thoracic radiographs, electrocardiography, echocardiography) helps determine the clinical picture in each patient.
• Technological advances have allowed smartphones to become valuable tools in the diagnosis and monitoring of heart disease.
• Pimobendan is now part of standard heart failure therapy in dogs with DMVD and DCM. The benefits of pimobendan and indications for its use continue to expand as the results of clinical trials are published.
• Interventional cardiology provides minimally invasive treatment options for a variety of acquired and congenital heart diseases.

ACDO = Amplatz canine ductal occluder; ACE = angiotensin-converting enzyme; CHF = congestive heart failure; DCM = dilated cardiomyopathy; DMVD = degenerative mitral valve disease; ECG = electrocardiogram; NT-proBNP = N-terminal pro–B-type natriuretic peptide; PDA = patent ductus arteriosus; RRR = resting respiratory rate

Disclosure Statement

Dr. Saunders has received research funding and programmatic support from Boehringer Ingelheim Vetmedica (manufacturer of VETMEDIN) and IDEXX Laboratories (providers of Cardiopet proBNP Test).

References

1. Hezzell MJ, Boswood A, Chang YM, et al. The combined prognostic potential of serum high-sensitivity cardiac troponin I and N-terminal pro–B-type natriuretic peptide concentrations in dogs with degenerative mitral valve disease. J Vet Intern Med 2012; 26(2):302-311.
2. Oyama MA. Using cardiac biomarkers in veterinary practice. Vet Clin North Am Small Anim Pract 2013; 43(6):1261-1272.
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6. Haggstrom J, Boswood A, O’Grady M, et al. Effect of pimobendan or benazepril hydrochloride on survival times in dogs with congestive heart failure caused by naturally occurring myxomatous mitral valve disease: The QUEST study. J Vet Intern Med 2008; 22(5):1124-1135.
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8. Summerfield NJ, Boswood A, O’Grady MR, et al. Efficacy of pimobendan in the prevention of congestive heart failure or sudden death in Doberman pinschers with preclinical dilated cardiomyopathy (The PROTECT Study). J Vet Intern Med 2012; 26(6):1337-1349.
9. Gordon SG, Saunders AB, Roland RM, et al. Effect of oral administration of pimobendan in cats with heart failure. JAVMA 2012; 241(1):89-94.
10. MacGregor JM, Rush JE, Laste NJ, et al. Use of pimobendan in 170 cats (2006–2010). J Vet Cardiol 2011; 13(4):251-260.
11. Gordon SG, Saunders AB, Achen SE, et al. Transarterial ductal occlusion using the Amplatz® canine duct occluder in 40 dogs. J Vet Cardiol 2010; 12(2):85-92.

Ashley B. Saunders, DVM, Diplomate ACVIM (Cardiology), is an associate professor of cardiology in the Department of Small Animal Clinical Sciences at Texas A&M University College of Veterinary Medicine and Biomedical Sciences. Her interests include interventional cardiology and advanced imaging, heart failure management, and educational technology. She is the recipient of multiple teaching awards and is a Montague Center for Teaching Excellence Scholar.