Learning Objectives

Analyze the mechanical phases of the left ventricle and their correlation to ECG triggers. Identify heart sounds (S1–S4) and their underlying pathophysiology in volume vs. pressure overload. Interpret JVP waveforms to diagnose right-sided heart pathologies like tamponade or tricuspid regurgitation. Predict how preload, afterload, and contractility alter the Pressure-Volume (PV) loop.

Phases of the Left Ventricular Cardiac Cycle

The cardiac cycle is the foundation of hemodynamics. For clinical practice, you must correlate electrical triggers (ECG) with mechanical events (valvular motion and pressure changes).

Isovolumetric Contraction

This occurs immediately after the QRS complex. The Mitral Valve closes (S1). The ventricle is a closed chamber; pressure rises sharply while volume remains constant. This phase has the highest myocardial oxygen demand (MVO2).

Systolic Ejection:

Once LV pressure exceeds aortic pressure (~80 mmHg), the Aortic Valve opens. Blood is forced into the aorta. The volume remaining at the end of this phase is the End-Systolic Volume (ESV).

Isovolumetric Relaxation:

Following the T-wave, LV pressure drops below aortic pressure, causing the Aortic Valve to close (S2). The ventricle relaxes with both valves shut.

Ventricular Filling:

The Mitral Valve opens when LV pressure falls below atrial pressure. Filling occurs in three stages: Rapid Filling (80% of volume), Diastasis (slow filling), and Atrial Systole (the final 20% “Atrial Kick”).

Heart Sounds and Clinical Significance

• S1: Closure of Mitral and Tricuspid valves. Best heard at the apex. Marks the onset of systole.
• S2: Closure of Aortic and Pulmonary valves. Best heard at the base. Physiologic splitting occurs during inspiration due to increased venous return, delaying PV closure.
• S3 (Ventricular Gallop): Occurs during the rapid filling phase of diastole. It signifies volume overload and is common in HFrEF or Mitral Regurgitation.
• S4 (Atrial Gallop): Occurs during atrial contraction. It indicates blood striking a stiff, hypertrophied ventricle (e.g., Aortic Stenosis, Long-standing Hypertension).

Jugular Venous Pulse (JVP) Waves

• a wave: Right Atrial contraction. Lost in Atrial Fibrillation. Large “cannon” waves are seen in AV dissociation.
• c wave: Carotid transmission or Cusp bulging of the tricuspid valve during ventricular contraction.
• x descent: Atrial relaxation. This is absent or reversed in Tricuspid Regurgitation.
• v wave: Venous filling of the atrium against a closed tricuspid valve. Giant v-waves are seen in Tricuspid Regurgitation.
• y descent: Atrial emptying. Absent in Cardiac Tamponade; very rapid in Constrictive Pericarditis (Friedreich’s sign).

Pressure-Volume (PV) Loop Adjustments

Activity