[RC] Definition of Murmurs and Arrhythmias from the Merck Vet Manual. - Katrina Mosshammer
Murmurs:
Heart murmurs are audible vibrations
emanating from the heart or major blood vessels and generally are
the result of turbulent blood flow or vibrations of cardiac
structures such as part of a valve leaflet or chordal structure.
Murmurs are typically defined relative to timing, intensity, and
location, but can also be characterized by frequency (pitch),
quality (eg, musical), and configuration (eg,
crescendo-decrescendo). A systolic murmur occurs during
systole and is typically either ejection (crescendo-decrescendo) or
regurgitant (holosystolic, plateau). Ejection systolic murmurs
demonstrate the greatest intensity during mid-systole and appear
diamond-shaped on phonocardiography. They can be produced by
stenotic lesions at the semilunar valves (eg, pulmonic stenosis or
subaortic stenosis). Regurgitant systolic murmurs demonstrate a
constant intensity throughout systole and can be caused by mitral or
tricuspid regurgitation (eg, myxomatous degeneration of the mitral
valve). Diastolic murmurs are typically decrescendo
(decreasing in intensity through diastole) and a result of aortic or
pulmonic insufficiency (such as that caused by aortic valve
infective endocarditis). Continuous murmurs are most commonly
a result of patent ductus arteriosus (a congenital cardiac defect)
and occur throughout systole and diastole. Continuous murmurs vary
in intensity over time, typically being most intense at the end of
ventricular ejection and decreasing in intensity through diastole. A
to-and-fro murmur occurs in patients that demonstrate both a
systolic murmur and a diastolic murmur and can occur in patients
with a ventricular septal defect and aortic valve insufficiency or
in a patient with subaortic stenosis and aortic
insufficiency.
In horses, early systolic and
diastolic murmurs can be noted in the absence of heart disease or
anemia. The point of maximum intensity is typically located over the
left heart base. A short, high-pitched, squeaking, early diastolic
cardiac murmur is sometimes seen in healthy young horses.
Occasionally, systolic murmurs are noted in some cats secondary to
an increase in right midventricular flow velocity without
significant structural heart disease. Innocent cardiac murmurs are
also commonly noted in immature cats and dogs (<6 mo of age) as a
result of increased stroke volume.
Heart murmurs are classified as
follows: Grade I?the lowest intensity murmur that can be heard,
typically detected only while auscultation is performed in a quiet
room; Grade II?a faint murmur, easily audible, and restricted to a
localized area; Grade III?a murmur immediately audible when
auscultation begins; Grade IV?a loud murmur immediately heard at the
beginning of auscultation but not accompanied by a thrill; Grade V?a
very loud murmur with a palpable thrill, the loudest murmur that is
still inaudible when the stethoscope is just removed from the chest
wall; or Grade VI?an extremely loud murmur that can be heard when
the stethoscope is just removed from the chest
wall.
Arrhythmias:
Arrhythmias are abnormalities of the
rate, regularity, or site of cardiac impulse formation and are noted
during auscultation. Other terms such as dysrhythmia and ectopic
rhythm are also used to describe arrhythmias. The presence of a
cardiac arrhythmia does not necessarily indicate the presence of
heart disease; many cardiac arrhythmias are clinically insignificant
and require no specific therapy. Some arrhythmias, however, may
cause severe clinical signs such as syncope or lead to sudden death.
Numerous systemic disorders may be associated with abnormal cardiac
rhythms. (For discussion of specific arrhythmias, see Electrocardiography.)
