Transcript Chapter 11 Slides

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Atrial Fibrillation
In atrial fibrillation (AF), chaotic and rapid atrial contractions cause an irregular
ventricular response,.
This impairs ventricular filling and cardiac output and thus can lead to a variety
of symptoms:
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Fatigue
Decreased exercise capacity
Pre-syncope, or syncope, falls
Stroke
Basic Pathophysiology
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• Atrial fibrillation is one of the most common cardiac arrhythmias, and it
occurs more frequently with advancing age.
• It is believed to be caused by multiple reentrant circuits within the atria.
• Atrial fibrillation often occurs with other cardiovascular conditions,
particularly chronic heart failure, cardiomyopathy, valvular disease,
coronary artery disease, hypertension, and hyperthyroidism.
• Some of these disorders may be underlying causes of AF, and in some cases
they may be manifestations of AF.
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Management and Medications
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Medical management of AF primarily involves two basic approaches:
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• Converting the heart back to normal sinus rhythm (convert the individual
back to sinus rhythm through electrical cardioversion, radiofrequency
ablation, or a surgical method - many individuals return to AF within 4 to 6
weeks.)
• Controlling the ventricular rate response [(Medicines used to control the
ventricular rate in AF include Digoxin, β-blockers (e.g., propranolol, sotalol,
metoprolol, atenolol, and Nondihydropyridine calcium channel blockers (e.g.,
diltiazem, verapamil)]
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AF patients are at a high risk for stroke and must be anticoagulated. The
irregular heart rhythm leads to small eddies of blood that don’t flush
through the chambers very well, which can lead to formation of a
thrombus that can be ejected from the heart and cause a stroke.
Antithrombotic therapy reduces the risk of stroke by up to ≈80%.
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Atrial Fibrillation
Effects on the Exercise Response
Patients with AF have a rapid, irregular ventricular rate.
• Heart rate is comparatively high at any level of exercise, in part to
compensate for the diminished stroke volume
• Maximal heart rate tends to be higher, although there is variability in
the maximal heart rate response (standard deviations up to 30
beats/min)
• The heart rate response is also affected by comorbid
conditions commonly associated with AF (e.g., coronary artery
disease, chronic heart failure)
• Stroke volume is reduced in AF (reduced atrial systolic function)
• Because of the variability in the diastolic filling period, determination
of systolic blood pressure can be difficult and is poorly reproducible
• Exercise tolerance is generally reduced in AF - this reduction is
typically about 20%, but it is highly dependent on the presence and
extent of underlying heart disease
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Atrial Fibrillation
Effects of Exercise Training
Insufficient scientific literature is available concerning the effects of exercise
training specifically in people with AF (typically a comorbid condition - AF
associated with CAD)
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The major concerns during exercise training are symptoms of AF due to
inadequate medical management (rate control)
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Atrial fibrillation can be very difficult to endure.
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• The trial of medical management, electrophysiology studies, and
pacemaker adjustment sounds simple, but in practice it often
takes months before there is successful and sustained rate control.
• Many patients with AF find this frustrating and can really benefit
from an exercise specialist who can help them through this period
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Atrial Fibrillation
Recommendations for Exercise Testing
• Maximal exercise testing can be safely used to measure the functional
capability of individuals with AF
• Exercise testing is also helpful in determining the effectiveness of ratecontrol therapy, and moderately incremented treadmill protocols are
warranted.
• The reduction in exercise capacity associated with AF is a direct function of
the underlying heart disease
• In the absence of other clinical indications for stopping, persons with AF
may be safely taken to fatigue or shortness of breath endpoints
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Contraindications to exercise testing in AF are mostly related to
comorbidities and other underlying conditions, such as the following:
• Instability of chronic heart failure
• Valvular disease
• Complex ventricular arrhythmias
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Atrial Fibrillation
Recommendations for Exercise Testing
Interpretation of the exercise electrocardiogram (ECG) is made more difficult
in AF because many individuals with AF take medications to control the rate
response and have underlying heart disease.
• Digoxin helps to control the ventricular response during exercise, but
it also has diffuse effects on the ST-segment response, including
false-positive (ECG) changes.
• Other AV nodal suppressants, including calcium channel blockers
and β-blockers, can mask ischemic changes, and β-blockers are likely
to reduce exercise capacity
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Atrial Fibrillation
Considerations for Exercise Testing in Atrial Fibrillation
• Digoxin: may control ventricular response; diffuse ST effects
• Verapamil: may mask ischemia and decrease heart rate response to exercise
• Diltiazem, verapamil: help control ventricular response; may improve exercise
capacity
• β-blockers: help control ventricular response; may reduce exercise capacity,
particularly with nonselective medications; decrease submaximal and maximal
heart rate and blood pressure
• Bundle branch block: common in people with AF; makes determination of
ischemia difficult
• Left ventricular hypertrophy: common in persons with AF; makes
determination of ischemia more difficult
• Age-predicted maximal heart rate targets: not valid
• Irregular ventricular response: may make blood pressure determination less
precise or more difficult
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Recommendations for Exercise Programming
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Major factors to consider in exercise programming for individuals with AF:
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• Daily variation in ventricular rate
• In some cases, the intermittent nature (presence or absence)
of AF
• Inherent unreliability of the pulse rate for prescribing exercise
intensity
• Adequacy of anticoagulation in those on anticoagulation
therapy
• Concomitant or underlying heart disease
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Since AF is frequently accompanied by underlying cardiac disease,
exercise programming for these conditions is the major consideration
in selecting goals and rate of progression.
Atrial fibrillation can have day-to-day variations in ventricular response
that can lead to symptoms of low cardiac output (pre-syncope, syncope).
This assessment is an important precaution before beginning every
exercise session
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Recommendations for Exercise Programming
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Because AF has a variably irregular ventricular response rate, exercise intensity
cannot be based on heart or pulse rate but should be prescribed based on work
rate and perceived exertion.
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Frequency, duration, intensity, and progression of exercise are similar to those
for individuals in normal sinus rhythm and can follow standard ACSM Guidelines.
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AF can be intermittent. The rhythm should therefore be determined every day.
This influences the patient’s heart rate response to exercise, exercise
tolerance, and level of fatigue.
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It is also important to note that AF has varied effects; some patients
experience fatigue while others do not.
Finally, many people with AF are elderly, and one must consider comorbid
conditions such as osteoporosis, coronary disease, diabetes, and obesity
when developing the exercise program.
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Recommendations for Exercise Programming
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Several precautions should be considered during exercise programming:
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• Longer sampling of the pulse may be needed to reliably measure heart rate.
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• Atrial fibrillation has varied effects; some people experience fatigue, while
others do not.
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• Atrial fibrillation is frequently intermittent, so ascertain rhythm daily.
Many with AF are elderly, so consider comorbid conditions.
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