Cardiovascular · 3 min read
Cardiac A&P and Hemodynamics
The heart functions as a dual pump with four chambers. The right side receives deoxygenated blood from the systemic circulation and pumps it to the lungs; the left side receives oxygenated blood from the pulmonary circulation and pumps it to the body. Cardiac output (CO) = heart rate × stroke volume, and stroke volume depends on preload, afterload, and contractility.
Conduction System
The sinoatrial (SA) node is the primary pacemaker, firing at 60–100 beats/min. Impulses travel through internodal pathways to the atrioventricular (AV) node, which delays conduction so the atria can empty before ventricular contraction. The bundle of His, the right and left bundle branches, and the Purkinje fibers then distribute the impulse rapidly through the ventricles.
Coronary Circulation
The left main coronary artery bifurcates into the left anterior descending (LAD) and circumflex arteries. The right coronary artery (RCA) supplies the inferior wall, the right ventricle, and in most people the SA and AV nodes. Coronary perfusion occurs mainly during diastole, so tachycardia (which shortens diastole) reduces myocardial oxygen supply while increasing demand.
| Artery | Myocardium Supplied | ECG Leads | Watch For |
|---|---|---|---|
| LAD | Anterior wall, anterior septum | V1–V4 | Pump failure, heart failure, bundle branch blocks |
| Circumflex | Lateral wall, posterior wall | I, aVL, V5–V6 | Posterior MI (ST depression V1–V3) |
| RCA | Inferior wall, RV, SA and AV nodes (most people) | II, III, aVF | Bradycardia, AV blocks, RV infarction |
Determinants of Cardiac Output
| Parameter | Normal Value | Reflects |
|---|---|---|
| Cardiac output (CO) | 4–8 L/min | Global pump performance |
| Cardiac index (CI) | 2.5–4.0 L/min/m² | CO adjusted for body size |
| CVP / right atrial pressure | 2–6 mmHg | Right-sided preload |
| PA pressure | 20–30 / 8–15 mmHg | Pulmonary vascular pressure |
| PAOP (wedge) | 8–12 mmHg | Left-sided preload |
| SVR | 800–1,200 dynes·s/cm⁵ | Left ventricular afterload |
| SvO₂ / ScvO₂ | 60–75% / above 70% | Oxygen supply–demand balance |
| MAP | 70–105 mmHg (target 65 or higher) | Organ perfusion pressure |
- MAP = (SBP + 2 × DBP) ÷ 3. A MAP of at least 65 mmHg is the usual perfusion target.
- Low CO with high SVR and high PAOP = cardiogenic pattern. Low PAOP with high SVR = hypovolemic pattern.
- Inferior MI (RCA) is the classic cause of bradycardia and heart block in ACS.
Finished reading?
Lock it in with a quick Cardiovascular quiz.