Why do we take a right-sided lateral X-ray for calculation of VHS?
Reading Document
Medical Text Search
VHS vertebral heart score right lateral radiograph positioning rationale
Medical Image Search
VHS vertebral heart score lateral chest radiograph measurement
GradeResponse
GradeResponse
The database didn't return text results on this specific topic, so I'll answer from established veterinary radiology knowledge, supplemented by the image retrieved.
Why Is a Right Lateral (Right Recumbent) Radiograph Used for VHS?
The Vertebral Heart Score (VHS) — originally described by Buchanan & Bücheler (1995) in dogs — standardizes cardiac size by expressing the sum of the heart's long axis (LA) and short axis (SA) in vertebral body units, measured from T4 on a lateral thoracic radiograph.
The right lateral recumbency is the standard because of several anatomical and physiological reasons:
1. Cardiac Position and Sternal Contact
When the animal is in right lateral recumbency, the heart falls toward the sternum and lies in a more consistent, reproducible position within the thorax. In left lateral recumbency, the heart tends to rotate and shift more freely away from the sternum (since the left side is now "up"), introducing positional variability in the cardiac silhouette that makes measurements less reproducible.
2. Reduced Cardiac Rotation
The interventricular septum and the cardiac apex have a natural orientation that is better aligned and less rotated in right lateral recumbency. This means:
- The long axis (base to apex) is more truly representative of the actual long axis of the heart.
- The short axis (widest perpendicular dimension) is less affected by oblique projection artifacts.
3. Lung Inflation is More Consistent
In right lateral recumbency, the left (upper) lung is better inflated because it is non-dependent. Better lung inflation means:
- Greater contrast between the heart and the surrounding lung parenchyma.
- A cleaner, sharper cardiac silhouette that allows more precise axis measurements.
4. Standardization for Normative Data
The reference ranges and normative VHS values (e.g., 9.7 ± 0.5 vertebrae in dogs) were established from right lateral radiographs. Using a left lateral would yield slightly different measurements and make comparison to published norms invalid. Consistency is essential for VHS to be clinically meaningful across institutions and over time for the same patient.
5. Minimal Positional Artefact of the Caudal Vena Cava
The caudal vena cava (CVC), which is sometimes assessed alongside VHS, is also better visualized in right lateral recumbency due to its anatomical relationship to the diaphragm and liver.
Summary Table
| Reason | Right Lateral | Left Lateral |
|---|---|---|
| Heart position | Stable, against sternum | More mobile, variable |
| Cardiac axis alignment | More reproducible | Subject to rotation artifact |
| Lung aeration (upper lung) | Better (left lung up) | Variable |
| Matches normative database | ✅ Yes | ❌ No |
| CVC visualization | Better | Suboptimal |
In practice, if only a left lateral is available, VHS can still be estimated, but the result must be interpreted cautiously and not directly compared to right-lateral normative values, as the measurements can differ by ~0.5–1 vertebral unit.
how frequently can u administer ivermectin to dogs
Medical Text Search
ivermectin dosing frequency administration dogs
GradeResponse
The retrieved result covers human pharmacology only. I'll answer from established veterinary pharmacology knowledge.
Ivermectin Dosing Frequency in Dogs
The frequency depends entirely on the indication, since ivermectin is used at very different dose levels for different conditions.
1. Heartworm Prevention
- Dose: 6–12 mcg/kg orally
- Frequency: Once monthly
- This is the most common use (e.g., Heartgard). Monthly dosing is sufficient because it acts as a "pulse" that eliminates L3/L4 larvae deposited in the previous 30 days.
2. Generalized Demodicosis (Demodex canis)
- Dose: 300–600 mcg/kg orally (daily dose, titrated up gradually)
- Frequency: Once daily until two consecutive negative skin scrapings (typically weeks to months of treatment)
- Dose escalation is recommended — start at 100 mcg/kg/day and increase by 100 mcg/kg every 1–2 weeks to reduce the risk of toxicity.
3. Sarcoptic Mange (Sarcoptes scabiei)
- Dose: 200–400 mcg/kg orally or SC
- Frequency: Every 1–2 weeks, typically for 3–4 treatments
4. Ear Mites (Otodectes)
- Dose: 200–400 mcg/kg SC or orally
- Frequency: Repeat in 2 weeks (two doses total)
5. Microfilaricide (after adulticidal therapy)
- Dose: 50 mcg/kg orally
- Frequency: Single dose, given 3–4 weeks after adulticide treatment to clear circulating microfilariae
⚠️ Critical Safety Notes
| Concern | Detail |
|---|---|
| MDR1/ABCB1 mutation | Collies, Australian Shepherds, Shelties, and related breeds may carry the ABCB1-1Δ mutation, making them highly sensitive to ivermectin toxicity even at standard doses. Genetic testing is recommended before use. |
| Toxic dose | Neurological signs (ataxia, tremors, blindness, coma) occur at doses ≥2,500 mcg/kg in normal dogs, but much lower in MDR1-affected dogs. |
| Heartworm-positive dogs | Do NOT use ivermectin at microfilaricidal doses in dogs with high microfilarial burden without proper pre-treatment — risk of anaphylactoid reaction. |
| Puppies | Use with caution in puppies under 6 weeks; blood-brain barrier is less mature. |
Quick Reference
| Indication | Dose | Frequency |
|---|---|---|
| Heartworm prevention | 6–12 mcg/kg | Monthly |
| Demodicosis | 300–600 mcg/kg | Daily |
| Sarcoptic mange | 200–400 mcg/kg | Every 1–2 weeks |
| Ear mites | 200–400 mcg/kg | Once, repeat in 2 weeks |
| Microfilaricide | 50 mcg/kg | Single dose |
Always confirm the ABCB1 genotype in susceptible breeds before initiating any ivermectin regimen beyond monthly heartworm prevention doses.
What about if I use it for tvt
Medical Text Search
ivermectin TVT transmissible venereal tumor dogs treatment
GradeResponse
No results retrieved — answering from veterinary oncology knowledge.
Ivermectin for TVT (Transmissible Venereal Tumor) in Dogs
Ivermectin has been investigated as an adjunct or alternative treatment for TVT, primarily based on its reported antitumor and immunomodulatory properties at higher doses.
Dosing Protocol
- Dose: 200–600 mcg/kg orally or SC
- Frequency: Once weekly
- Duration: Typically 4–8 weeks, assessed by tumor response
Some protocols report weekly administration continued until complete tumor regression, confirmed by cytology or biopsy.
Important Context
Ivermectin is not a first-line treatment for TVT. The gold standard remains:
| Treatment | Protocol | Response Rate |
|---|---|---|
| Vincristine (VCR) | 0.5–0.7 mg/m² IV weekly × 4–6 doses | >90% complete remission |
| Ivermectin | 200–600 mcg/kg weekly | Variable; used where vincristine is unavailable |
| Doxorubicin | Reserved for vincristine-resistant cases | High efficacy |
| Radiation therapy | Used for resistant/extragenital TVT | Effective |
Ivermectin is most relevant in resource-limited settings where vincristine is not accessible, or as an adjunct when conventional chemotherapy is not feasible.
Mechanism (Why It May Work Against TVT)
- Inhibits P-glycoprotein (P-gp/MDR1), potentially reversing multidrug resistance in tumor cells
- Induces mitochondrial dysfunction and apoptosis in neoplastic cells
- Modulates the immune microenvironment around the tumor
⚠️ Safety Reminder
The weekly dosing used for TVT is significantly higher than heartworm prevention doses. The MDR1/ABCB1 mutation risk in susceptible breeds still applies — screen before use. Monitor for signs of ivermectin toxicity (mydriasis, ataxia, hypersalivation, tremors) after each dose.
Bottom line: For TVT, ivermectin is given once weekly for 4–8 weeks, but vincristine remains the preferred treatment where available due to its superior and well-documented efficacy.
This is a shared conversation. Sign in to Orris to start your own chat.