Understanding Normal and Abnormal Heart Rhythm
Learning Objectives: Heart Rhythm
- Practice ausculting the cadence of the normal heart rhythm
- Palpate precordium and arterial pulse simultaneously to detect any pulse deficits
- Auscult the heart and palpate arterial pulse simultaneously to detect any pulse deficits
- Detect a sinus arrhythmia, if present in your group’s dog.
Cardiac Arrhythmias
- Isolated premature beats or pairs or short bursts of premature beats result in disturbances to the cadence of the heart rhythm.
- Normal rhythm is interrupted, and there can be a pause after the abnormal beat.
- These premature beats can arise from the atrial or ventricular regions, and an ECG would be necessary to determine the origin of the abnormal beats.
- Arrhythmias can cause increased or decreased heart rates.
- Pulse deficits are a good indicator that an arrhythmia is present.
Syncope – An important clinical concept:
“Syncope” is a loss of consciousness due to lack of cerebral blood flow. If an arrhythmia interrupts normal cardiac function enough to interrupt this blood flow, syncopal events can occur. Exercise intolerance and weakness can also be observed in patients with reduced blood flow secondary to impaired cardiac function. Events that excessively slow the heart rate can cause syncope. Additionally, sustained tachycardia (that does not allow for heart chamber filling before ejection of blood) can also result in syncope. Syncope can be difficult to differentiate from seizures. One differentiating feature is that animals usually do not have changes before or after the syncopal event (in contrast to seizures, in which patients often have “pre-ictal” & “post-ictal” phases which are times before / after the seizure characterized by changed behaviour and other features).
Cardiac disease other than arrhythmias can also cause syncope – examples include heart changes that do not allow for adequate filling of the heart and/or adequate pumping of blood forward. Specific examples include hypertrophic cardiomyopathy in cats, dilated cardiomyopathy in dogs. These concepts will be emphasized later in the curriculum.
Respiratory sinus arrhythmia:
- Normal or physiological phenomenon detected in some patients.
- Heart rate speeds up in when patients breathes in; heart rate slows down when patient breathes out.
- A regular rhythm, usually in synchrony with respiration.
- Occurs at normal heart rate, tends to disappear when heart rate increases.
- Not associated with pulse deficits. Intensity of pulse can vary.
Examples of Audio Clips:
Other Heart Sounds:
Gallops:
- Result in a tripling or quadrupling of the heart sounds, resembling the canter of a horse
- Best heard with the bell of the stethoscope
- May be an early finding in ventricular failure
Clicks:
- Abnormal sounds
- Very high frequency sounds
- Most commonly associated with mitral valve disease
- Uncommon finding overall in small animals, but mainly found in dogs, not cats