4.1 Cardiac Anatomy & Physiology Refresher

Why this matters for the NPTE-PTA

The Cardiovascular and Pulmonary Systems content area is one of the larger system blocks on the NPTE-PTA: the Federation of State Boards of Physical Therapy (FSBPT) 2024 content outline assigns it roughly 20-27 items (data collection 5-8, diseases/conditions 7-9, interventions 8-10) out of the 180-question exam, about 11-15% of items. The full exam is 180 multiple-choice questions (150 scored, 50 unscored pilot items) delivered in a single 4-hour Prometric session, and you need a scaled score of 600 on the 200-800 scale to pass.

Mastering the cardiac plumbing first makes the monitoring and stop-exercise items later in this chapter almost automatic.

Coronary Anatomy

The heart is fed by two main coronary arteries branching off the aorta:

• Left main coronary artery divides into the Left Anterior Descending (LAD) and the Left Circumflex (LCx). The LAD supplies the anterior wall and most of the interventricular septum and is the most common site of large myocardial infarctions (MIs) - the 'widow-maker.' Anterior MIs threaten pump function and ejection fraction.
• Right Coronary Artery (RCA) typically supplies the right ventricle, inferior wall, the sinoatrial (SA) node, and the atrioventricular (AV) node in most people. Inferior MIs (RCA) frequently produce bradycardia and heart block because the conduction nodes lose their blood supply - watch for an HR that fails to rise during PTA-led activity.

The Cardiac Cycle in One Pass

1. Diastole - ventricles relax and fill (the longer phase at rest; shortens as HR climbs).
2. Atrial kick - atria contract and top off ventricular filling (lost in atrial fibrillation, dropping CO by up to 20-30%).
3. Isovolumetric contraction - all four valves closed, pressure builds.
4. Ventricular ejection - aortic and pulmonic valves open; blood leaves the heart.
5. Isovolumetric relaxation - aortic/pulmonic valves close (the dicrotic notch), then mitral/tricuspid valves open and diastole restarts.

Cardiac Output and Ejection Fraction

Cardiac Output (CO) = Heart Rate (HR) x Stroke Volume (SV). Resting CO is about 4-8 L/min and can climb to 20-25 L/min in trained athletes. During exercise HR rises first; SV plateaus around 40-60% of maximal effort. When HR cannot rise - beta-blockers, sick sinus syndrome, an RCA infarct - CO climbs slowly and the patient fatigues early, so you must lean on perceived exertion rather than an HR target.

Ejection Fraction (EF) = Stroke Volume / End-Diastolic Volume. A normal EF is about 55-70%.

Normal Adult Resting Vital Signs

Calculating a Training Heart Rate

Two methods appear on the NPTE-PTA, and the exam loves to test whether you remember to add resting HR back in.

Percent of HR Maximum (HRmax)

HRmax (estimate) = 220 - age. Target HR = HRmax x intensity percent. This ignores resting HR and conditioning, so it underestimates the true workload needed for a deconditioned patient.

Karvonen (Heart Rate Reserve)

Heart Rate Reserve (HRR) = HRmax - Resting HR. Target HR = (HRR x intensity percent) + Resting HR. Karvonen is preferred in cardiac rehabilitation because it personalizes the prescription to the patient's resting HR.

Worked example: a 60-year-old (HRmax = 160) with a resting HR of 80 prescribed 60% intensity has a Karvonen target of (160 - 80) x 0.60 + 80 = 128 bpm. The simpler percent-of-HRmax method gives 0.60 x 160 = 96 bpm - far too low to drive a conditioning response. Always show the +resting-HR step when you check your work.

Pressures, Preload, and Afterload

Three more concepts surface in NPTE-PTA exercise-physiology items. Preload is the volume stretching the ventricle at end-diastole; by the Frank-Starling mechanism, more preload produces a stronger contraction and a larger stroke volume, up to a point. Dehydration or major blood loss lowers preload and stroke volume, so the patient compensates with a higher resting HR. Afterload is the resistance the ventricle must overcome to eject - chiefly the systolic blood pressure and aortic valve.

High afterload (uncontrolled hypertension, severe aortic stenosis) makes the heart work harder for the same output, which is why those conditions appear on the absolute-contraindication list later in this chapter.

Contractility is the intrinsic strength of the squeeze, independent of preload and afterload; it falls after a large MI or in dilated cardiomyopathy and is reflected by a low ejection fraction. When you read a chart, connect the dots: a low EF means low contractility, which means the patient relies heavily on raising HR to keep cardiac output up during your session - exactly the patient who fatigues fast and needs frequent rests.

Practical Takeaway for the PTA

Because cardiac output is the product of HR and stroke volume, anything that caps either factor caps the patient's exercise ceiling. Beta-blockers, pacemakers, and conduction-system MIs cap HR; heart failure, valve disease, and hypovolemia cap stroke volume. When the exam describes one of these, expect the right answer to involve lower-intensity starts, perceived-exertion monitoring instead of HR targets, and closer vital-sign surveillance rather than aggressive progression.