Sunday, July 24, 2011
Notes from July 2011 St. Louis AVMA Conference-Xrays and Echos
These are papers from the July 2011 St. Louis AVMA conference. I’ve edited them to delete some of the vet only jargon and for space considerations. If you see (…) that means that information has been deleted due to these considerations. The ones listed here include HCM, and other heart related papers, treatments, papers on x-rays and echos, thrombosis, kidney disease, idiopathic cystitis, pain management, anesthesia and cardiac disease, supplements and other hazards for pets, and some other basic information I hope is helpful.
Systematic Approach to Thoracic Radiographs: Why is this patient coughing?
Deborah M. Fine, DVM, MS, DACVIM (cardiology)
Coughing is a common presenting complaint seen with both respiratory and cardiovascular
disease. Coughing is a protective reflex mechanism that occurs when cough receptors located
throughout the respiratory tract (larynx, pharynx, and bronchi) are stimulated. The most
frequent causes of cardiogenic cough are left-sided congestive heart failure with pulmonary
edema, and left mainstem bronchial compression secondary to left atrial enlargement…
Congestive heart failure in the cat does not typically cause coughing. Coughing in feline patients is almost invariably due to underlying pulmonary or airway disease such as asthma or heartworm disease.
Non-cardiac causes of cough are much more numerous and include diseases of the upper and
lower airways, and pulmonary parenchyma. Upper airway diseases that can cause cough
include collapsing trachea, infectious tracheobronchitis, tracheitis, foreign body, or laryngeal
and tracheal masses. Lower airway causes of cough include feline asthma, as well as chronic
or eosinophilic bronchitis. Pulmonary parenchymal diseases include infectious and noninfectious
pneumonitis, neoplasia, non-cardiogenic pulmonary edema, and various interstitial
lung diseases such as pulmonary fibrosis…
A thorough physical examination will often provide clues to the underlying disease process.
Auscultatory findings of heart murmurs, abnormal heart sounds (gallops, clicks, split S1 or S2
heart sounds), or arrhythmias may suggest underlying cardiovascular disease. However,
abnormal heart sounds do rule-out primary respiratory disease as the cause of cough, as
these may be incidental distractions. Wheezing may suggest lower airway involvement, while
stridor may indicate upper airway involvement. Crackles can be due to heart failure or primary
pulmonary disease…The absence of tachycardia in a patient with coughing or respiratory distress,
regardless of the presence of a murmur, usually rules-out
heart failure. Thoracic radiography is an invaluable diagnostic test to help ascertain the cause
of cough. Additionally, serial thoracic radiographs are useful for determining response to
therapy and progression of disease.
THORACIC RADIOGRAPHIC INTERPRETATION
Technique and Positioning
Proper technique and positioning is vital to accurate interpretation…Magnification of the ventral lung fields
improves pulmonary parenchymal evaluation. For optimal visualization of pulmonary nodules,
all four orthogonal views should be obtained.
Although viewers often use the terms “heart” and “cardiac silhouette” interchangeably, it is
important to remember that this structure on a radiograph simply represents the overall size of
the pericardium and its contents. If the cardiac silhouette is interpreted as enlarged, then the
next question becomes “what is causing the enlargement”? Differentials would include an
actual increase in the size of the heart, presence of pericardial effusion, neoplastic mass, or
herniation of abdominal contents into the pericardium (peritoneal pericardial diaphragmatic
hernia). Frequently, additional imaging is necessary to make a final determination.
The size of the cardiac silhouette is evaluated relative to the thorax. In lateral projections, the
heart width typically spans 2.5 to 3.5 intercostal spaces. The height of the heart from apex to
the carina should occupy no more than 2/3 of the thoracic cavity. On DV or VD projections,
the maximal width of the heart should be no wider than the width of the hemi-thorax at the 9th
rib. A vertebral heart scale (VHS) system was developed in an attempt to provide a more
objective determination of cardiac size. Using the lateral view, the long and short axes of the
heart are measured. The measurements are then superimposed over the vertebral column,
both starting at the cranial edge of T4, and the number of vertebrae covered is then summed….Normal cats have a VHS of 7.2 to 7.8. …In cats, left atrial enlargement is best appreciated in DV and VD projections where it may result in a widening of the heart base, commonly referred to as a valentine-shaped heart…
Pulmonary Vascular Abnormalities
Evaluation of the pulmonary vasculature is crucial for distinguishing between causes of
respiratory signs. On the lateral projections, the pulmonary vasculature is best visualized in
the cranial lung fields. The pulmonary arteries are dorsal to the bronchus, and the veins are
ventral. On DV/VD projections, the pulmonary vasculature is clearest in the caudal lung fields
with the pulmonary arteries located lateral to bronchus and the veins medial. The pulmonary
artery and veins should be symmetrical, and on the lateral projection they should be equal in
diameter to the width of the 4th rib. On DV/VD views, the pulmonary artery and vein should be
equal to the width of the 9th rib.
Enlargement of the pulmonary arteries is implicative of pulmonary arterial hypertension.
Depending on the region of the country, heartworm disease should be at the top of your
differential list with this finding. Primary pulmonary disease (e.g. COPD, asthma, bronchitis,
pulmonary fibrosis, etc.) can also cause pulmonary hypertension with resulting arterial
enlargement. Enlargement of the pulmonary veins is a hallmark feature of congestive heart
failure and is the result of increased left atrial and left ventricular diastolic pressure.
Symmetrical enlargement of both the arteries and veins indicates the combination pulmonary
hypertension and increased left atrial pressure is present. In a young animal, this would be
most likely due to a left to right shunting cardiac defect. In an older animal, this is most likely
due to a combination of left heart failure, and either primary pulmonary disease or pulmonary
hypertension secondary to chronically increased left atrial pressure (e.g. chronic degenerative
mitral valve disease).
Pulmonary Parenchyma and Airways
Evaluating the pulmonary parenchyma and airways for specific lung patterns is vital in
distinguishing between cardiac and non-cardiac causes of cough. Abnormal radiographic lung
patterns are described as interstitial, alveolar, or bronchial. Frequently, a combination of
patterns is present in the same patient.
An interstitial pattern is recognized radiographically as an increase in the overall opacity of the
lungs. All of the normal structures are still visible, but the margins have a hazy quality.
Interstitial lung patterns appear as an increase in the opacity of the lung fields with indistinct or
hazy pulmonary vasculature…An alveolar pattern is characterized by complete loss of margins of the pulmonary vasculature, and the presence of air bronchograms. An air bronchogram is caused by fluid or cells filling
the terminal alveoli, which results in a uniform soft tissue opacity surrounding the radiolucent
bronchus. Alveolar patterns can occur with pulmonary edema, pneumonia, hemorrhage,
atelectasis, lung lobe torsion or from cellular infiltration of the alveoli. A bronchial pattern is
caused by thickening of the airways, either from inflammation or mineralization of the airways
themselves (e.g. asthma, bronchitis) or interstitial fluid tracking along the airway margins.
Radiographically this appears as “donuts” and “tramlines”.
Cardiogenic pulmonary edema initially appears as interstitial to bronchointerstitial. As heart
failure progresses the interstitium becomes saturated, causing the fluid to spill into the alveoli.
Cardiogenic pulmonary edema is typically bilaterally symmetrical. In the dog, edema is most
prominent in the caudodorsal and perihilar lung fields. In cats, cardiogenic pulmonary edema
is usually located in the ventral lung fields, although a patchy, diffuse distribution can also be
seen. Large volume pleural effusion as a manifestation of heart failure is much more common
in cats than in dogs…
Thoracic radiography in conjunction with a thorough physical examination is beneficial in
assessing the primary cause of a cough in veterinary patients. Radiographs can assist in
determining if the cough is cardiac or respiratory in origin and can be useful in following
progression and resolution of the disease process. Cases discussed in this session will provide
examples of how thoracic radiographs help distinguish whether coughing is due to primary
respiratory or cardiovascular disease and emphasize the common radiographic changes seen
in these disease processes.
References available upon request.
Electrocardiography: What's It Really Good For?
Deborah M. Fine, DVM, MS, DACVIM (Cardiology)
University of Missouri
A diagnostic ECG can provide information about the following:
1. Arrhythmias: the ECG is the gold standard for diagnosis of arrhythmias, and this is by far its
most important application.
2. Conduction system abnormalities: shifts in the mean electrical axis, (right- and left bundle
branch blocks, fascicular blocks, and right ventricular hypertrophy), or atrioventricular heart
blocks can signify serious underlying cardiac disease.
3. Enlargement of cardiac chambers can be suggested by the ECG: tall P wave = R atrial
enlargement, wide P wave = L atrial enlargement, tall R wave = L ventricular enlargement.
4. Electrolyte abnormalities (especially hyperkalemia): characteristic changes in ECG
morphology have been associated with some electrolyte abnormalities.
What is the difference between “monitoring” and “diagnostic” electrocardiography?
ECG monitoring is performed to check for heart rate and rhythm abnormalities during
anesthesia and in ICU patients. The ECG obtained using monitoring equipment is highly
filtered to provide a stable baseline and to reduce motion/electrical artifacts. Monitoring ECG's
are often recorded with patients and recording electrodes placed in "non-standard" positions.
Filtering and patient/electrode position can have a marked impact on the morphology of the
ECG complexes. Consequently, we cannot use monitoring ECG's to measure various
amplitudes, durations, etc. of complexes. Diagnostic ECG's are used to determine rate,
rhythm, mean electrical axis, and to measure the amplitude and duration of the complexes.
Diagnostic ECGs are obtained with equipment using much less filtering and are consequently
more sensitive. The trade-off is that it is much less forgiving in terms of motion and electrical
artifacts. The patient and leads must be in the standard positions for a diagnostic ECG.
What are the limitations of diagnostic electrocardiography?
An ECG provides no information about the mechanical or contractile status of the heart…An animal with advanced heart failure may have a normal ECG, and a perfectly normal animal may show non-specific electrocardiographic
abnormalities. Additional diagnostic procedures (e.g., thoracic radiographs, echocardiography)
are necessary for complete evaluation of a cardiology case…