Using radiography to diagnose heart enlargement : Mild to moderate heart enlargement indicates mild to moderate progression of mitral regurgitation MR , with the heart compensating for the effects of mitral regurgitation by enlarging. Usually the dog displays no outward signs or symptoms of MVD when moderate to severe heart enlargement develops, until the dog reaches the stage of heart failure. VHS measurements to detect enlargement: Cardiologists use x-rays to evaluate the size and shape of the heart in order to assess the severity of MVD. Since the dog's own vertebrae are used for comparison, each VHS vamue is normalized to the dog's overall body size.
See this YouTube video for details. A diagram showing how the VHS is calculated is here. James W. Buchanan , a pioneer in the research of MVD in cavaliers, in See his article. It's purpose is to enable veterinarians to more accurately determine enlargement of the heart called cardiomegaly or dilatation or dilation and the progression at which the enlargement is occurring, which usually is due to MVD. See for example, the x-ray at left, which shows that the VHS measurements entirely miss the bulbous enlarged LA in the upper right corner of the heart.
Image from Hezzell, Technically, the measurement is described as:. The investigators compared these x-ray measurements with echocardiographic measurements of the left atrium of each dog, using two standard echo images of the LA: a left atrium-to-aortic root ratio acquired from short-axis LA:AoSx and b long-axis LA:AoLx.
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They conclude:. Radiographic Left Atrial Dimension RLAD : In a December article , a team of European cardiology researchers report having devised an addendum to the verterbral heart size VHS method of measuring heart size using x-rays in order to measure just the size of the left atrium. See Figure 1, rght. They performed these measurements on the x-rays of 77 dogs, 31 in group 1 of which had no left atrial enlargement and included one cavalier King Charles spaniel , and 46 mixed breed dogs in group 2, all of which reportedly did have enlargement of the left atrium.
They concluded:. Subjective analysis of x-rays of MVD-affected hearts: A more subjective method of determining heart enlargement from x-rays is to compare the shape of the left artium LA and left ventricle LV to the known customary shapes of normal canine hearts, particularly of the same breed. The cardiologists look for a more rounded appearance, bulging, and other deviations from the typical normally shaped heart, and whether the heart is impacting the trachea, in addition to the size of the heart.
For moderate LAE, that bump would be clearly enlarged but not huge. For severe LAE, the bump would appear to be huge on the x-rays. Commonly used criteria for LAE include what are called "Roentgen signs" named after the discoverer of the x-ray. These signs are: 1 elevation of left mainstem bronchus, 2 loss of curvature of the caudal heart, 3 straightening of the caudodorsal margin of the cardiac silhouette, 4 increased height of cardiac silhouette, 5 divergence of mainstem bronchi, 6 double opacity LA, and 7 enlarged bulging left atrium.
Instead, the enlarged LV is more rounded than a flatter, normal sized LV. In the x-ray above Fig. In the x-ray at right, the severely enlarged heart is in the center of the photo, beneath the horizontal spinal column. The LA is the bulging upper right corner. The LV is the rounded portion on the right side, beneath the LA. To compare x-rays of the left ventricle LV in a better perspective, here at the left are computer-designed models of a normal sized LV on the left and an enlarged LV on the right.
Note that the healthy LV is flatter elliptical , and the enlarged LV is wider and rounded globular. Image from Ljungvall, et al. John Bonagura has described the appearance of an enlarged LV as a "squashed mushroom".
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Quality and standardization of x-rays : A downside of relying upon x-rays to detect heart enlargement is the necessarily subjective analyse of the films. Even experienced board certified cardiologists will argue over whether a single set of x-rays shows left side enlargement or not, and if so, its degree. This usually is due to poor positioning of the dog during the x-rays, which is not uncommon.
Two x-rays of the same dog, even taken at the same session, can vary the appearance of the heart. Variations can be due to 1 the stage of the dog's respiration inhaling versus exhaling , 2 the stage of the heart's contraction, 3 the centering of the x-ray beam, and 4 the position of the dog on the x-ray table, among a few causes. Ideally, all x-rays should be taken as close to the dog's peak inhalation of its breath as possible. This may be very difficult when the x-rays are taken digitally, because there may be a delay between pushing the button and the actual x-ray beam.
Even with perfect timing, the heart size changes with each beat -- systole contraction and diastole relaxation. Standardization of x-rays of MVD-affected dogs is very important to assure that when two sets of x-rays of the same dog are compared, the cardiologist is looking at the same position and timing of the dog's heart. Maybe a board certified cardiologist can tell from x-rays alone that the LA or LV is enlarged, but as noted above, even they will disagree from time to time, and especially if the positioning of the dog even flexing the neck can cause misleading shadowing and quality of the films are less than perfect, or the dog was inhaling in one view and exhaling in another or sedated in one and not in the other.
See also, this November article , which concluded:. Baseline and periodic x-rays : Baseline x-rays are a set of radiographs taken either before or immediately after an MVD murmur is detected. The baseline x-rays are used to compare to later sets to determine if the heart as enlarged. Periodic x-rays of the cavalier's heart, showing the rate of its enlargement, are viewed by many cardiologists as an effective way to anticipating the onset of heart failure HF. The series of x-rays at left shows the increase in heart size of one cavalier over 5 years.
The amount of enlargement of the left atrium mild, moderate, or severe enlargement usually correlates with the degree of mitral regurgitation MR -- mild, moderate, or severe MR. A formula used by cardiologists to predict when onset of heart failure will occur, is to determine the change in the vertebral heart scale between two x-rays taken within a year of each other, divided by the number of months between those two x-rays.
If that number is equal to or higher than 0.
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However, this formula is not error-proof and should not be the sole determining factor in predicting or diagnosing the onset of heart failure. Mark A. Oyama and by the authors regarding this study. See also this November article which focused specfically on the Dachshund.
Diagnosing pulmonary edema: Chest x-rays also are the only diagnostic imaging modality that can accurately tell if the MVD-affected dog has pulmonary edema fluid building up in the lungs , meaning has reached the point of congestive heart failure. Using radiography to diagnose heart failure: X-rays can identify pulmonary edema or pleural effusion.
Identifying pulmonary edema on an x-ray alone does not confirm a diagnosis of heart failure, because pulmonary edema may have other causes. Therefore, to confirm heart failure as the cause of the edema, there must also be mitral valve regurgitation and enlargement of the left side of the heart. Pulmonary edema is shown on x-rays as an in the interstitial density of the lungs. The more severe the edema, the more dense will be the interstitial markings.
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Angiography and Angiocardiography: Angiocardiograms are x-rays made while a radioactive fluid is inected and is circulating through the heart. The fluid is injected through a catheter into the left ventricle, to observe regurgitation through the affected valve. This procedure has been utilized in MVD-affected dogs since the mids. See this January article authored by Dr.
See this comparison between a standard x-ray of a dog's heart at leftand an angiogram of the same heart at right, below. The CTR is calculated as the percentage of the cardiac silhouette related to the thoracic area. The CTR was proposed in a September article by a team of Brazilian researchers, using a scheme previously proposed by others for assessing human heart enlargement. Using the "dorsoventral" x-ray of the dog's heart see the photo at right here, from the article , the CTR is calculated by adding the largest distance from the heart's vertical center line to the right side of the heart MR and the largest distance from that line to the left side ML.
Then divide that combined amount by the greatest thoracic diameter MTD. In a January article , Romanian researchers reported that the CTR method can discriminate the normal from modified heart size, diagnosed according to the VHS score, in small breed dogs. Manubrium Heart Score MHS : In a February article , researchers proposed assessing cardiac enlargement based upon comparing the length of the dog's manubrium the handle-shaped, broad upper part of the sternum, from which the clavicles and first ribs extend.
The manubrium of the sternum was selected because, the article stated, "it is a relatively prominent, regularly elongated, bullet-shaped or rectangular bone segment that is easily identified and can be readily measured on lateral thoracic radiographic views.
Dexmedetomidine often is used to sedate dogs before heart x-rays and echocardiographs. In a January report , researchers examined the effects of dexmedetomidine on six heart-healthy dogs undergoing chest x-rays and echocardiograms to determine if the sedative caused any changes in the resulting measurements. They found that the x-rays and echos performed after dosing dexmedetomidine resulted in significantly higher measurements of the vertebral heart score and cardiac size, and that moderate to severe mitral regurgitation and mild pulmonary regurgitation occurred in all six dogs.
An ever increasing respiratory rate called tachypnea , while the dog is asleep, which approaches or exceeds 30 breaths per minute, is an indication that the dog is approaching heart failure. Once a dog is diagnosed with MVD and the disease has been progressing, the treating veterinarian may ask the dog's owner to periodically count the number of breaths the dog takes per minute while asleep, and to keep a record of those counts. In an October study , researching cardiologists found that healthy adult dogs generally have mean sleeping respiratory rates SRR of less than 30 breaths per minute and rarely exceed that count.
While the dog is sound asleep but not showing signs of dreaming , count the number of breaths the dog takes in 15 seconds. A rise inhale and fall exhale of the chest count as one full breath or respiration. Then multiply that number by four to get the number of breaths per minute. If that respiratory rate increases by more than 20 percent over 2 to 3 days, or regularly exceeds 30 breaths per minute, many treating veterinarians would advise the dog's owner to report to them.
In a study which compared the effectiveness of a respiratory rate, b natriuretic peptide concentration, and c echocardiogram, in predicting heart failure, the respiratory rate count was more accurate than both of the other procedures. The researchers stated:. Every cavalier owner can and should learn this very simple procedure of how to count the breaths of their MVD-affected dogs while they are sleeping.
An excellent YouTube video shows when and how every cavalier owner can count the breaths of their MVD-affected dogs while they are sleeping or at rest.
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