Herp Cardiology

Question 1

What embryonic aortic arches persist and what do they become?

What is the heart shape of chelonians, ophidians, lizards, and crocodilians?

Where is the heart positioned in snakes, chelonians, lizards, and crocodilians?

What species lack a gubernaculum cordis?

Answer 1

• Cardiac Anatomy and Physiology:
  
  • Noncrocodilians – Two atria, one ventricle.
    
    • Basic embryonic pattern common to reptiles, birds, mammals.
      
      • Six aortic arches – 3, 4, 6 persist in reptiles.
      • Right AA, left AA, and pulmonary trunk formed from ventral aorta.
      • Right and left systemic arches merge caudally to form common dorsal aorta.
      • These three efferent arterial trunks produce one pulmonary circuit and two systemic circuits, each arising independently from the heart.
  • Cardiac size, shape, and position.
    
    • Heart mass compared to total body mass 0.2-0.3%,,similar to amphibians.
      
      • Varies, larger in more athletic species.
    • Shape of heart is broad and globoid in chelonians, elongated in ophidians, ovoid in lizards and crocodilians.
    • Location of heart – most along axial midline, cranial within coelom.
      
      • Snakes variable. Marine and FW snakes, closer to middle of body.
      • Non-tree-dwelling snakes, about 25% snout-to-vent length, more cranial in arboreal spp.
        
        • A cranial heart position reduces hydrostatic pressure above heart, stabilizes variations in cephalic BP.
          
          • Arboreal and climbing snakes raise their heads often, have shorter vasculature between heart and head.
          • Reverse for aquatic spp with minimal gravity effect.
        • Heart adjacent to caudal tracheal rings, caudal to thyroid, cranial to bronchial bifurcation, close to cranial pole of lung(s), cranial to liver.
        • “Precordial tap” can be visualized externally.
      • Chelonians – located ventral midline at intersection of humeral, pectoral, and abdominal plastron scutes.
        
        • Bordered dorsally by septum horizontale and cranial lungs, laterally by liver lobes, and ventrally by coelomic membrane and plastron.
        • Displaced to the right in soft-shelled turtles due to long protractile neck which moves displacement of heart and liver to right and stomach to left when retracted.
      • Lizards – heart within pectoral girdle.
        
        • In tegus, Gila monsters, monitor lizards, heart located more caudally in coelom.
      • Crocodilians – location midway between pelvic and pectoral girdles.
        
        • Apex deep between right and left medial hepatic lobes, adjacent to liver isthmus.
        • Base extends slightly cranial to border of liver, within mediastinum ventral to primary bronchi and esophagus.
  • Pericardium.
    
    • Heart apex attached to pericardium by gubernaculum cordis.
      
      • Except snakes and varanids, free within pericardial sac.

Question 2

What are the two patterns of the reptilian heart?

Noncrocodilians

• How many chambers?
• What are the three subchambers of the ventricle?
• How many aortic arches are there?
• What are the two ventricular septa?
• How do these septa function during contraction?
• What are the two types of noncrocodilian cardiac morphologies? What species exhibit each?

Crocodilians

• How many chambers?
• The left ventricle ejects blood into which vessel? What about the right ventricle?
• What is the foramen of panizza?
• Where else do the R and L aortic arches connect?

Answer 2

• Heart Anatomy.
  
  • Two basic patterns:
    
    • Noncrocodialian heart (squamates, chelonians).
    • Crocodilian heart (crocodiles, alligators, gavials, caimans).
  • Noncrocodilians:
    
    • Three-chambered, two atria, one ventricle.
    • Ventricle partially partitioned by muscular ridges.
      
      • Contrast with four-chambered crocodilian heart with complete interventricular septum.
    • Ophidian heart.
      
      • Larger right atrium.
      • Three arterial trunks – left aortic arch, right aortic arch.
        
        • Right aorta (not left) branches off several major arteries including the carotids, fuses caudally with left aorta to form the common abdominal (dorsal) aorta.
        • Pulmonary artery later divides into L and R pulmonary arteries to supply left and (if present) right lung.
        • In spp with one predominant right lung i.e. most ophidians, left pulmonary artery is absent or vestigial.
    • Sinus venosus on dorsal heart, attached to dorsal wall of ventricle by dorsal ligament.
      
      • Contains pacemaker, contractile tissue.
      • Receives deoxygenated blood from two cranial VC and caudal VC drains into right atrium through a sinoatrial orifice with sinoatrial valves.
      • Some spp – hepatic vein or jugular vein also drains directly into the sinus venosus.
      • SV has a partial septum in most squamates.
        
        • SV sometimes considered an additional ‘chamber’, aka atypical four-chambered heart.
      • In squamates, LA generally smaller than RA, receives blood from two pulmonary veins.
        
        • Some spp have paired valves between pulmonary veins and atria.
        • Atria communicate with ventricle via atrioventricular funnels, separated from ventricle by monocuspid atrioventricular valves.
        • AV valve-complex – bell-shaped, concave side faces ventricle.
        • Fibrous strands similar to chordae tendinae join the AV valves to the ventricular musculature.
    • Ventricle subdivided into three subchambers – cavum pulmonale, cavum venosum, cavum ateriosum.
      
      • Cavum venosum and arteriosum are mostly dorsal (collectively aka cavum dorsale), and to the cavum pulmonale is ventral (aka cavum ventral).
    • L and R aortic arches arise from cavum venosum at two orifices with bicuspid valves (unlike tricuspids in mammals).
    • Pulmonary trunk is a continuation of the cavum pulmonale, base contains small semilunar valves.
    • In some spp of chelonians and squamates, foramen connects the R and L aortas, unknown significance. Both aortas arise from the cavum venosum.
    • Two ventricular septa.
      
      • Muscular ridge aka horizontal septum from apex to base of heart, incomplete at base.
        
        • Separates cavum pulmonale from cavum venosum/cavum arteriosum during ventricular systole.
          
          • Poorly developed in chelonians, except marine turtles and giant tortoises.
          • More developed in varanids and pythons.
          • The IV septum present in crocodilians and birds seems to have evolved from this ridge.
      • Vertical septum aka interventricular septum divides cavum dorsale into cavum arteriosum to left and cavum venosum to right, often joins muscular ridge at base.
        
        • Contributes to separation of pulmonary venous blood from systemic flow during ventricular diastole.
    • Another septum – bulbus lamelle, opposite muscular ridge.
    • Large interventricular canal connects cavum arteriosum and cavum venosum.
      
      • AV valves, when opened, compress toward midline and obstruct the IV canal.
      • Allows a functional separation of systemic and pulmonary circulation, with cavum pulmonale (cavum ventral) being the functional homologue to the mammalian, crocodilian, and avian right ventricle.
      • Cavum venosum and arteriosum (cavum dorsale) – functional homologue to mammalian, croc, and avian left ventricle.
      • Cavum venosum receives both oxygenated and deoxygenated blood during cardiac cycle.
    • Two kinds of cardiac morphologies in noncrocodilian reptiles:
      
      • Continuous single chamber, operates as a single pump during cycle.
        
        • Most chelonians and squamates, most lizards.
        • Muscular ridge relatively small, not well developed.
        • Right aortic and intraventricular pressures equal.
      • Varanid and python – large, well-developed muscular ridge.
        
        • almost forms complete ventricular septum, also visualized as asymmetric thick wall.
        • Also found in leatherback turtles.
        • Cavum arteriosum enlarged, cavum venosum reduced.
        • Cavum pulmonale becomes functionally separated from the cavum venosum and from the cavum arteriosum during systole.
          
          • Functions as a double pump, higher pressures in cavum venosum and systemic arches than in cavum pulmonale and pulmonary arteries.
          • This complete separation clearly shown in varanids, Burmese python, and ball python.
  • Crocodilians.
    
    • Four-chambered.
    • Complete interventricular septum.
    • Divides pulmonary and systemic blood flow.
    • Gubernaculums cordis – ligament from right ventricle (not from apex as in Testudines and Sauria), anchors heart to pericardium.
    • Sinus venosus reduced, partial septum internally.
      
      • Resembles an elongated pyramid, with base cranial and apex caudal.
      • L and R atria same size.
      • Both aortic arches remain.
      • LV ejects blood into right aorta, RV ejects blood into left aorta, pulmonary artery.
      • All three vessels similar diameter.
        
        • Cranially, both aortae and pulmonary artery bound together by CT sheath.
        • At base of each efferent artery is a bicuspid valve, medial cusp longer than lateral.
        • Foramen of panizza – connection between left and right aortic arches, shorly after exit from ventricles.
      • Bicuspid atrioventricular valves guard connection between atria and ventricles, composed of left septal and right marginal cusp.
      • Left AV valves membranous.
      • Marginal cusp of right AV valve is thick, liplike.
      • Pulmonary veins have no valves (same as mammals).
        
        • Right and left aortic arches anastomose at two locations – Foramen of Panizza and level of midcoelomic cavity by dorsal connecting artery.
        • Opening of the FOP is actively controlled.

Question 3

Describe the cardiac physiology of the reptile heart.

Do they have a Purkinje system?

Where do contractions originate?

How does temperature affect myocardial efficiency?

What other physiologic factors affect heart rate?

Answer 3

• Cardiac Physiology:
  
  • Pacemaker and HR.
    
    • No pacemaker nodes or Purkinje fibers.
    • Contractions initiated by cardiac muscle.
      
      • Originate in fibers within sinus venosus of RA, spread first to left and then toward apex caudally.
      • Ventricle depolarized starting at base, proceeding to left.
      • Repolarized from base, spreads symmetrically to right and left towards apex.
      • Specific areas of cardiomyocytes slow conduction, seen as delays on ECG.
        
        • Rapid systolic phase, far slower diastolic.
        • Myocardium of ventricle functions as medium for conduction and contraction.
    • Heart innervation – parasympathetic and sympathetic.
      
      • PS fibers in vagus nerve, cholinergic (inhibitory) control.
      • Sympathetic fibers – positive chronotropism, inotropism via adrenergic innervation.
    • HR – slower in reptiles.
    • Myocardial efficiency optimum in POTZ.
      
      • Tachycardia at higher temps, with peripheral vasodilation increases heat loss from cutaneous vascularization.
      • Lower temps stimulate bradycardia, peripheral vasoconstriction, reduce heat loss.
      • Regulated by cutaneous thermoreceptors.
        
        • HR proportional to metabolic level and inversely proportional to body size.
        • Hypovolemia may lead to tachycardia.
        • Bradycardia also observed during apnea as pulmonary resistance increases and blood flow to lungs decreases, effectively creating R to L cardiac shunt.
          
          • Other effects on HR – digestion, gravidity, sensory stimulations i.e. handling, postural, gravitational stress, methylatropine, certain anesthetics and sedative i.e. alpha 2 agonists

Question 4

Describe the flow of blood through the noncrocodilian heart during normal breathing?

What areas of the ventricle receive oxygenated blood, which receive deoxygenated blood?

How are they kept separate without a complete septum?

Compare that with the flow through the crocodilian heart during normal breathing.

Answer 4

• Blood flow during normal breathing:
  
  • Noncrocodilians.
    
    • Pulmonary and systemic flow separated and regulated by functional plasticity.
      
      • Ox and deox blood form aortic arches partially mixed, amount of mix determined by degree of evelopment of the muscular ridge and IV septum.
      • Early ventricular diastole – both AV valves open, block IV canal between cavum arteriosum and cavum venosum.
        
        • CV and pulmonale receive deox blood from RA, CA receives ox blood from LA.
      • Late ventricular diastole – blood flow from atria ceases, deox blood from cavum venosum flows into cavum pulmonale.
      • During ventricular systole – AV valves close, opens IV canal, allows blood from CA into CV.
      • Late systole – muscle ridge moves cranial, separates CV and CP.
        
        • Ox blood pumped from CV into L and R aorta, deox blood pumped from CP to pulmonary arterial trunk.
    • Due to diastolic BP being lower in pulmonary arches, blood flows through pulm arteries and then systemic arteries.
    • Ventricular systole is long, diastole short.
    • In varanids, puthons, muscular ridge nearly complete, produces more pronounced separation of flow and allows for higher BP.
      
      • Chelonians – cavum venosum much larger, more blood mixing occurs.
      • Unlike mammals, reptilian atria make an active contribution to ventricular filling.

SV -> RA -> CV -> CP -> Pulmonary Trunk -> LA -> CA -> IV Canal -> CV -> Aortic Arches

• Crocodilians.
  
  • In air, heart functions similar to mammals – separate systemic and pulmonary circulations
    
    • Blood pressures in L and R aorta equalized via foramen of Panizza (opens during ventricular diastole) and the dorsal connective artery.
      
      • Bicuspid valve of left aorta (exiting right ventricle) remains closed.
        
        • All blood in the right ventricle pumped into pulmonary circulation.
        • Blood in left ventricle goes into right aorta, as one of the valves guarding the right aorta folds back to cover the foramen of Panizza during systole.

Question 5

Descrbe the flow of blood through a noncrocodilian heart during a dive.

What is the difference between pressure shunting and washout shunting?

How does this differ with crocodilians?

Answer 5

• Blood Flow during Cardiac Shunting
  
  • Noncrocodilians
    
    • SV -> RA -> CV -> Aortic Arches
    • Pulmonary Flow -> LA -> CA -> IV Canal -> CV ->Aortic Arches
    • High parasympathetic tone (rest, fasting, diving, apnea, hibernation) causes vasoconstriction in pulmonary vasculature resulting in R->L shunt
    • Increased sympathetic tone (high temps, exercise, digestion) produces pulmonary vasodilation resulting in a L->R shunt
    • Both pressure difference and washout shunting occur in these species
      
      • Washout Shunting
        
        • Primarily washout mechanism for more developed python & varanids
        • During systole, most deoxygenated blood from CV goes to CP but some remains
          
          • When oxygenated blood from CA enters the CV it creates a R->L shunt
        • During diastole, deoxygenated blood from RA to CV & CP will mix with oxygenated pulmonary venous blood resulting in a L-R shunt
          
          • The degree of L->R shunting depends on the amount of blood coming back from the pulmonary vasculature
        • Depended on preload, contractility of the heart, and afterload
  • Crocodilians
    
    • During apnea, increased pressure in lung tissue & with valves at base of pulmonary artery increase pulmonary resistance
    • The pressure of the RV becomes greater than that of the LV
      
      • Blood from RV enters LAo & PA (mostly LAo)
      • Some blood from LAo goes to RAo through the FP resulting of mixing of oxygenated and deoxygenated blood

Question 6

What diagnostic methods (not imaging) are avialalbe to evaluate reptile hearts?

What are some common clinical signs of reptiles with heart disease?

What is the best way to auscultate a reptile?

How useful are blood pressure and pulse oximetry measurements in reptiles?

What values in bloodwork may be elevated in reptiles with heart disease?

Describe the proper placement of ECG leads on various species

Answer 6

• Diagnostic tools in reptile cardiology:
  
  • PE.
    
    • CS – swelling around cardiac region (cardiomegaly), cyanosis, peripheral/gular edema, pulmonary edema, ascites, and exercise intolerance.
    • Syncope, arrhythmias.
    • Brain anoxia secondary to heart failure and atherosclerosis may cause neurologic signs i.e. ataxia, head tilt.
    • Coughing not observed due to lack of diaphragm.
    • Heart failure:
      
      • Mammals – blood volume regulated by renal and GI systems.
      • Reptiles (esp lizards), additional osmoregulatory organs i.e. salt glands.
      • CS – pulm edema, coelomic effusion.
    • Major differences vs mammals – ability to shunt blood, having a single ventricle.
  • Auscultation.
    
    • Pressure-sensitive acoustic stethoscopes.
    • Doppler. Indicates blood flow, not valve closure.
    • Reptile should be in POTZ for assessment of HR.
  • BP/pulse ox.
    
    • Cuff and doppler not reliable.
    • Direct BP accurate but require surgical exposure of artery, impractical.
    • Pulse ox measures mammal hemoglobin, less useful in reptiles.
  • Clinical pathology.
    
    • CK, LDH may increase with cardiac conditions i.e. myocarditis or infarct.
    • Dyslipidemia i.e. hypercholesterolemia asssoc with atherosclerosis in beardies.
    • Hypocalcemia with nutritional disorders can affect cardiac muscle. ECG abnormalities.
    • Cardiac troponins – troponin 1 and troponin T both regulatory proteins that control the Ca mediated interaction between actin and myosin.
      
      • Dx myocardial infarction in mammals.
      • Have not been assessed in reptiles, may be useful.
  • ECG.
    
    • Widened QRS and lengthened QT interval in green iguana with aortic stenosis and AV dilatation.
    • Tall and wide QRS complexes in carpet python with AV valve insufficiency.
    • Main challenges – low electrical amplitudes, parameters not established.
      
      • Record electrode positions, ambient temps.
    • P, QRS, T.
      
      • SV wave represented by depol of sinus venosus. Before P.
      • Followed by sinusal contraction, P wave followed by atrial contraction, R wave followed by ventricular contraction.
      • T wave ventricular repolarization.
    • Normal – P wave pleomorphism, very reduced Q and S deflections, prolonged QT vs mammals.
    • Electrode placement.
      
      • Snakes – cranial limb leads two heart lengths cranial and caudal limb leads two heart lengths caudal to heart.
      • Negative lead can be placed on right side, one heart length cranial to heart.
      • Positive lead can be placed on left, 60-75% distance from the head.
      • Neutral or ground lead should be on right side, across from positive lead.
      • Lizards with heart in pectoral girdle – two cranial limb electrodes on cervical region instead of forelimbs. Caudal electrodes on lateral body wall, cranial to pelvis.
        
        • Heart caudal to pectoral girdle, cranial electrodes should be placed on forelimbs or cranial coelom, caudal electrodes on hindlimbs or torso.
      • Four-limb placement not appropriate in chelonians.
        
        • Low surface voltage.
        • Two cranial eletrodes should be placed in cervical region, lateral to neck and medial to forelimbs.
        • Caudal leads placed on cranial skin fold of stifles or caudally to pelvic limbs.

Question 7

Descibe the imaging modalities used to evaluate the reptile heart.

What are some of the challenges of using radiography?

Describe the placement of gel in reptiles to enhance echo imaging.

Where is the heart located in soft-shelled turtles and pancake tortoises?

What are the standard windows used to evaluate the heart?

Answer 7

• Diagnostic imaging.
  
  • Radiography.
    
    • Heart cannot be visualized in chelonians and crocodiles.
      
      • Obscured by pectoral girdle in lizards.
      • CT is better.
      • Rads can be used to evaluate the size of the cardiac silhouette in monitor lizards and snakes.
      • DV and horizontal beam recommended. Craniocaudal view in chelonians for lung fields.
      • Mineralization of great vessels may be observed if hypervitaminosis D3 or other metabolic disturbances.
  • CT, MRI.
    
    • CT better resolution, better for lung tissue and bone tissue.
    • MRI preferred for soft tissues i.e. CNS, liver, repro system, kidneys.
    • Not useful for visualizing moving cardiac structures.
      
      • Sedation/Ax generally required, may be contraindicated with heart failure.
  • Echo.
    
    • US/doppler most practical dx tool for antemortem evaluation of heart dz, visualization of blood flow within heart.
    • B-mode US, doppler, contrash echo described for ball pythons, Hermann’s tortoises, Russian tortoises.
    • Smaller reptiles will require higher MHz transducer.
      
      • Linear probe used in snakes and lizards, biconvex scanner recommended for chelonians due to small acoustic windows.
      • Apply get 10 min prior to exam to allow penetration between scales.
      • Shoft-shelled turtles and pancake cortoises, heart is more on the right side.
      • Can echo neonatal or juvenile chenonians and crocs when ventral scutes have yet to become mineralized.
      • Standardized 2D echo approach published for boid snakes and bearded dragons.
      • Some echo techniques reported in FW and terrestrial chelonians.
      • The chapter goes into a lot of detail about views, see images at end of this summary.
  • Endoscopy is limited, can evaluate surface of the heart and myocardium if pericardium transparent.
    
    • i.e. gout, neoplasia, or pericardial effusion.

Question 8

Describe the noninfectious cardiac diseases of reptiles?

What congenital abnormalities have been reported?

What cardiomyopathies have been reported?

What are some common pericardial diseases?

What neoplastic diseases occur in the heart?

Answer 8

• Cardiac diseases:
  
  • Reported – cardiomyopathy, septic endocarditis, valvular insufficiency, myocarditis, pericardial effusion, infarcts, atherosclerosis, aneurysms, gout, arterial calcification, thrombus, parasitic infestation, congenital heart defects, tumors.
  • Inadequate husbandry resulting in chronic stress, immune suppression, and malnutrition most likely predisposing factor for cardiovascular conditions in captive reptiles.
  • Noninfectious cardiac disease.
    
    • Congenital defects.
      
      • Rare.
      • Secundum atrial septal defect in Komodo dragon.
      • Snakes – ventricular mural hypoplasia with plasmacytic pericarditis, aortic valvular stenosis, enlarged/abnormal chambers, bifid ventricles, reduced muscular ridge with hemodynamic consequences.
      • Aortic and subaortic stenosis in iguanas, alligator.
    • Cardiomyopathies.
      
      • Described with CHF in variety of snakes.
      • Restrictive cardiomyopathy in carpet python.
      • Myocardial degeneration resulting from metabolic disorders i.e. gout, vit E and Se deficiencies.
      • Myocardial mineralization with excessive dietary Ca and vit D3. Aortic rupture assoc with aortic mineralization reported in lizards.
    • Noninfectious valvulopathies (valvulr endocardiosis).
      
      • No current evidence for primary degenerative endocardiosis in reptiles.
      • Might be a possibility, etiology not determined.
    • Pericardial diseases.
      
      • Visceral gout can lead to thickening with urate deposition.
      • Traumatic hemopericardium with hematoma in snakes following cardiac sampling.
      • Myocardial abscess in green iguana.
      • Pericardial effusion can be seen on US.
        
        • Small amount may be normal, volume measurement advised during necropsy.
    • Neoplasia.
      
      • Reported – cardiac rhabdomyosarcoma in a boa and king snake, cardiac hemangioma of LA in corn snake, hamangiosarcoma in copperhead and hognose snake, fibrosarcoma in viper, endocardial fibrosarcoma in retirulated python.
      • Mets to heart – metastatic chondrosarcoma, oviductal adenocarcinoma, MCT king snake, lymphoma loggerhead sea turtle, disseminated coelomic papillomas.
        
        • Disseminated coelomic papillomas affecting various organs, including the heart, were found in 39% of 255 stranded green turtles (Chelonia mydas) with fibropapillomatosis.

Question 9

Describe the infectious cardiac diseases of the reptile heart.

What bacterial organisms commonly infect the heart?

What parasitic organisms commonly infect the heart?

Answer 9

• Infectious cardiac disease.
  
  • Bacterial – endocarditis, myocarditis, pericarditis.
    
    • Commonly aerobic gram negative infection.
      
      • i.e. salmonella, Corynebacterium.
      • Salmonella arizonae, salmonella enterica.
      • Bacterial endocarditis can be observed with pneumonia.
      • Flavobacterium meningosepticum, vibrio damsel in myocardium.
      • Mycobacterium spp, chlamydophila spp.
      • Mycoplasma alligatoris – pericarditis, pheumonia and arthritis in American alligators.
    • Dx with US, hemoculture, post-mortem tissue culture (valves, myocardium, pericardium). Abx tx can be attempted.
  • Parasitic.
    
    • Encapsulated cestodes prevalence 5% in wild whiptail lizards.
    • Filarial nematodes can cause thrombosis, necrosis.
    • Macdonaldius oschei observed in fresh blood smears, myocardial histo.
    • Trematodes in heart chambers and major vessels of chelonians.
    • Green sea turtles – spirorchid flukes cause arteritis, endocarditis, thrombosis, aneurysms.
    • Spirorchid eggs and adult Learedius learei in heart of black sea turtles.
    • Besnoitiosis and sarcosporidiosis observed in histo of snake hearts.

Question 10

Describe the management of reptile cardiac disease.

What inotropes are commonly used in reptile heart disease?

What ACE inhibitors have been used?

Are diuretics still effective in reptiles?

Answer 10

• Treatment/management of cardiac disease:
  
  • Non-drug related management – reducing metabolic rates by maintaining lower end of POTZ, reducing stress, minimizing handling, separating from cage mates, do not overfeed (death in snakes with cardiomyopathy).
  • CHF – reduce volume of extracellular fluid and reduce preload.
    
    • Oxygen for dyspneic animals, may alter blood shunting.
  • Inotropes.
    
    • Alter force of muscular contractions.
      
      • Positive ionotropes enhance cardiac contractility.
        
        • Digoxin – positive ionotrope, negative chronotrope, positive lusitrope.
          
          • Increases cytosolic calcium concentration, inhibits Na/K ATPase pumps, increasing contractility. Used for afib.
        • Beta blockers i.e. atenolol and Ca channel blockers i.e. diltiazem – negative ionotropes for tx HCM in cats and SVT. Effect unknown in reptiles.
        • Atenolol significantly reduced resting HR and range of baroreceptor reflex in 15 iguanas. Did not affect the baroreceptor reflex function.
          
          • Upper HR plateau was lower after atenolol.
          • Methylatropine resulted in increased HR in same study, did not influence MAP.
            
            • Range of baroreceptor reflex substantially reduced.
      • ACE inhibitors.
        
        • Block formation of angiotensin 2, promotes venous and arterial asodilation, blocks aldosterone production and reduced preload and afterload through venous and arterial vasodilation.
          
          • Enalapril, benazepril in dogs and cats.
            
            • Enalapril inhibited angiotensin 1 conversion in alligators and was used briefly in a monitor with CHF.
  • Diuretics.
    
    • Increase water excretion and reduce fluid overload, decrease edema and effusions.
      
      • Reptiles have a metanephric kidney without a look of hendle.
        
        • However, furosemide has shown a diuretic effect in chelonians and ophidians.
        • Suggested mechanisms – species with a urinary bladder, Na:K pumps in the wall of the bladder are influenced by furosemide. Another hypothesis that furosemide may act on Na:K pumps in terminal colon and cloaca.
      • Use in caution in patients with renal disease, monitor ammonia, urea, uric acid during use.
      • Other diuretic use is lacking, personal comms.