A 52-year-old woman with a 10-year history of hypertension presents with progressive dyspnea on exertion and orthopnea. On examination, BP is 162/98 mmHg, HR 92/min (regular), with a prominent S4 gallop and no peripheral edema. Echocardiography shows a thick-walled left ventricle with normal cavity size, normal ejection fraction (LVEF 55%), and impaired early diastolic filling. Cardiac catheterization reveals elevated left ventricular end-diastolic pressure (LVEDP 28 mmHg) with a steep rise in diastolic pressure. Which of the following best explains the mechanism of reduced cardiac output and pulmonary congestion in this patient?

Explanation

## Diastolic Dysfunction and Cardiac Output Regulation **Key Point:** This patient has **diastolic heart failure (HFpEF — Heart Failure with preserved Ejection Fraction)**. The primary defect is impaired ventricular relaxation, not contractility loss. ### Pathophysiology of Diastolic Dysfunction **High-Yield:** In diastolic dysfunction: - **Systolic function is NORMAL** (LVEF 55%) - **Diastolic function is ABNORMAL** (impaired relaxation, increased stiffness) - The ventricle cannot relax and fill adequately during diastole ### Mechanism of Reduced CO and Pulmonary Congestion ```mermaid flowchart TD A[Chronic Hypertension]:::outcome --> B[LV Hypertrophy]:::outcome B --> C[Increased Myocardial Stiffness]:::outcome C --> D[Impaired Diastolic Relaxation]:::outcome D --> E{Ventricular Filling}:::decision E -->|Reduced| F[↓ Preload/EDV]:::outcome E -->|Requires Higher Pressure| G[↑ LVEDP]:::outcome F --> H[↓ Stroke Volume]:::outcome G --> I[Pulmonary Venous Congestion]:::outcome H --> J[↓ Cardiac Output]:::urgent I --> K[Dyspnea, Orthopnea]:::urgent ``` ### Clinical Findings Explained | Finding | Mechanism | |---------|----------| | **S4 gallop** | Atrial contraction against stiff ventricle (hallmark of diastolic dysfunction) | | **Elevated LVEDP (28 mmHg)** | Ventricle requires high filling pressure to achieve adequate preload | | **Steep diastolic pressure rise** | Loss of normal diastolic compliance; pressure rises sharply with small volume increases | | **Normal LVEF (55%)** | Systolic contraction is preserved; ejection fraction remains adequate | | **Orthopnea + dyspnea on exertion** | Pulmonary venous congestion from elevated filling pressures | | **No peripheral edema** | Primarily pulmonary congestion; systemic venous congestion less prominent | ### Why Cardiac Output is Reduced **The Frank-Starling Mechanism in Diastolic Dysfunction:** $$SV = f(EDV, \ Contractility, \ Afterload)$$ In this patient: - **EDV is reduced** because the stiff ventricle cannot fill adequately at normal diastolic pressures - **Contractility is normal** (LVEF preserved) - **Afterload is elevated** from hypertension (modest additional effect) Result: **Reduced preload → Reduced stroke volume → Reduced CO** **Clinical Pearl:** The elevated LVEDP is a **compensatory mechanism** to overcome the stiffness and achieve adequate filling. This comes at the cost of pulmonary venous congestion. ### Mnemonic: DIASTOLIC DYSFUNCTION - **D**ecreased relaxation (isovolumetric relaxation time prolonged) - **I**ncreased stiffness (myocardial fibrosis from chronic hypertension) - **A**dequate systolic function (normal EF) - **S**troke volume reduced (due to low preload) - **T**hick-walled ventricle (concentric hypertrophy) - **O**rthopnea and dyspnea (pulmonary congestion) - **L**eft ventricular hypertrophy (from chronic hypertension) - **I**ncreased filling pressures (LVEDP elevated) - **C**ardiac output reduced (despite normal contractility) ### Contrast with Systolic Dysfunction | Feature | Diastolic Dysfunction | Systolic Dysfunction | |---------|----------------------|----------------------| | LVEF | **Normal (>50%)** | **Reduced (<40%)** | | LV Size | Normal or small | Dilated | | S4 Gallop | **Present** | Absent | | S3 Gallop | Absent | **Present** | | Diastolic Filling | **Impaired** | Normal or hyperdynamic | | Contractility | **Normal** | **Reduced** | | LVEDP | **Elevated** | Elevated | | Mechanism of Low CO | Low preload (stiffness) | Low contractility | **Warning:** Do NOT confuse diastolic dysfunction with reduced contractility. The ejection fraction is normal; the problem is that the ventricle cannot fill adequately to generate sufficient stroke volume.