L&J Chi 26 Pathophysiology, Ax Management of Patients with CV Disease Flashcards
What are conditions associated with pressure overload?
Subaortic Stenosis
Pulmonic stenosis
Consequences of SAS
- Chronic systolic pressure increase in left ventricle
- Results in increased wall tension, compensatory increase in ventricular wall thickness (concentric hypertrophy)
Consequences of PS
- Chronic systolic pressure increase in right ventricle
- Results in increased wall tension, compensatory increase in ventricular wall thickness (concentric hypertrophy)
Consequences of concentric hypertrophy of L/R ventricle associated with SAS and PS?
Increase in ventricular muscle mass and increase in myocardial work required to generate increased systolic pressures –> increased demand for coronary blood flow and myocardial oxygen delivery
When is the resulting risk for ischemia the greatest?
-During periods of tachycardia –> myocardial necrosis, replacement fibrosis, development of ventricular arrhythmias
In young dogs with severe SAS
- Risk for syncope, sudden arrhythmogenic death is high
- Left-sided congestive failure only seen in much older dogs
Which is tolerated better?
Right concentric hypertrophy, even in cases of severe PS, appear to be better tolerated than cases of LV hypertrophy
In which condition (SAS or PS) is CHF more common?
PS
Chronic medical management of severe SAS, PS
Often involves beta blockers to reduce HR and myocardial oxygen demand
Echocardiography
-Useful to assess severity of SAS, PS lesion and extent of ventricular hypertrophy
Utility of Holter/24hr ECG in SAS, PS
- Evaluation of cardiac rhythm
- Detection of elevation/depression of ST segments which can be suggestive of myocardial ischemia
What drugs should be used with caution in SAS, PS patients?
Arterial vasodilators
-Decrease in arterial blood pressure increases the pressure gradient across stenotic valve –> can increase myocardial work, severe hypotension, and decreased coronary perfusion pressure
How common is PS?
Third most common heart defect in dogs
Pathophysiology of PS
- Obstruction to RV outflow tract increases resistance to injection so have a proportional increase in ventricular systolic pressure
- Concentric hypertrophy of RV occurs in an attempt to normalize wall stress (LaPlace’s Law)
- During systole, blood ejected from the RV accelerates as it travels the obstructive orifice –> blood velocity increases –> becomes turbulent as it travels through the obstructive orifice
- Poststenotic dilation develops in the main PA as turbulent jet flow decelerates and expends some of the kinetic energy against the wall
Consequences of RV Concentric Hypertrophy
- Reduces right ventricular diastolic compliance, which impairs ventricle’s ability to fill –> can result in increased RA pressure
- Tricuspid regurgitation from progressive ventricular dilation +/- valvular dysplasia can contribute to further increases in atrial pressure
- As RA pressure approaches 15 mm Hg, see signs of R CHF
What are clinical signs of R CHF?
Jugular distention
Ascites
Pleural effusion
Classifications of PS Severity
Mild
Moderate
Severe
What happens with dogs >125 mm Hg?
Frequently develop secondary tricuspid regurgitation, heart failure, exertion scope, serious cardiac arrhythmia
Mild
PG <50 mm Hg
Moderate
PG 50-80 mm Hg
Severe
PG >80 mm Hg
What are the types of PS?
Subvalvular, Valvular (A, B, Mixed), supravalvular
Valvular PS: Type A
- Most frequent
- Normal annular size with various degrees of valve leaflet thickening, incomplete separation of valve commissures to almost complete fusion
- Causes systolic doming of the valve
- Post-stenotic dilation of pulmonary trunk present with various degrees of severity
Valvular PS: Type B
- Hypoplastic osmium with various degrees of valvular leaflet thickening and immobility but little commissural fusion
- Main pulmonary trunk often hypo plastic –> rarely presents post-stenotic dilation
Valvular PS: Mixed type
A + B
Anesthetic Considerations for PS
- Poor ventricular compliance
- Avoid tachycardia to limit myocardial oxygen deficit
- Afterload is elevated but remains fixed due to stenosis at level of the valve so VD/reductions in vascular tone do very little to address after load so end up reducing preload, reduce coronary perfusion pressure
- Critically important to maintain adequate preload
Why is it important to maintain adequate preload in PS patients?
Maintaining adequate venous return by insuring a full intravascular volume to fill the non-compliant ventricle chamber will help optimize diastolic filling and CO
How is the severity of the obstruction accurately quantified?
- Peak velocity of blood flow jet recorded on spectral Doppler tracing acquired with continuous wave Doppler beam in parallel alignment with direction of flow
- Modified Bernoulli equation: P=4V^2
- Relates instantaneous pressure gradient across an obstruction to the peak velocity of the jet distal to the obstruction
What is important to remember about Doppler-derived gradients?
- 40-50% higher than the gradient measured during cardiac catheterization
- Doppler studies performed in awake dogs –> transvalvular flow considerably higher in these circumstances
Dilated Cardiomyopathy
- Idiopathic systolic dysfunction –> accompanied by eccentric dilation, volume overload
- Decrease in heart’s generation of normal forward stroke volume
- Resulting LV dilation –> dilation of MV annulus –> secondary MR that contributes to volume overload
DCM Breeds
-Large breed dogs –> Irish Wolfhound, Doberman Pinscher, Great Dane
Is DCM common in cats?
No, relatively uncommon since recognized taurine deficiency
–can see taurine deficiency in dogs fed grain-free diet
What see with DCM
- Mostly L CHF (pulmonary edema), sometimes R CHF (pleural effusion, ascites)
- Ventricular arrhythmias that can cause activity tolerance, syncope, sudden death
How diagnose, stage severity
ECG, echo, TXR
Also perform Holter monitoring to screen at-risk dogs for ventricular premature beats, which is an early sign of disease
Chronic DCM Therapy
- Reduction of preload - diuretics (furosemide, spironolactone)
- Reduction of afterload - ACEIs, pimobendan
- Increased contractility - positive inotropes (pimo, digoxin)
Acute DCM Anti-Arrhythmic Therapy
Lidocaine
Procainamide CRI
Chronic DCM Anti-Arrhythmic Therapy
Sotalol, amiodarone
Why use caution with beta blockers as anti-arrhythmic therapy with DCM?
Negative inotropic effects but use with caution in animals with severe systolic dysfunction or active CHF
AF and DCM
Common in Great Danes, Irish Wolfhounds, Mastiffs, other giant breeds
Consequences of AF
- Rapid ventricular rate associated with AF increases myocardial oxygen demand
- Reduces CO as diastolic filling time decreases
Treatment for AF
- Reduction of AV nodal conduction
- Slowing ventricular HR
- Drugs: Ca channel blockers (diltiazem), beta blocks, digoxin
Occult DCM
Asymptomatic
See unexplained VPCs before/during anesthesia that do not resolve
