Cardiovascular Anatomy and Clinical Assessment

The movement of electricity is driven by depolarization (the stimulation of muscle fibers to contract via changes in electrolyte concentrations, specifically the entry of $Na^+$ and $Ca^{2+}$) and repolarization (the return to a resting state as $Na^+$ and $Ca^{2+}$ channels close and $K^+$ is pumped in).

The autonomic nervous system regulates this rhythm:

• Sympathetic Stimulation: Releases norepinephrine to increase heart rate and strengthen the force of contraction.
• Parasympathetic Stimulation: Acts via the vagus nerve to release acetylcholine (ACh), which slows the SA node firing rate and conduction through the AV node.

Cardiovascular Disease and Acute Syndromes

Cardiovascular disease (CVD) is a broad term for disorders of the heart and blood vessels. A specific and common subset is Coronary Heart Disease (CHD), which affects the coronary arteries.

When blood flow to the myocardium is abruptly reduced, it can lead to Acute Coronary Syndromes (ACS), which include unstable angina, NSTEMI, and STEMI. If the blockage causes myocardial tissue death, it is classified as a Myocardial Infarction (AMI). A complete cessation of mechanical cardiac activity is known as cardiac arrest.

Clinical Note: When assessing a patient, always treat the patient, not the monitor. Arrhythmias must be evaluated within the context of the patient's overall clinical condition.

Clinical Assessment Techniques

Primary Survey

In emergency settings, the primary survey follows the ABCDE sequence: Airway, Breathing, Circulation, Disability, and Exposure. However, if a patient is unresponsive and cardiac arrest is suspected, the order shifts to CABDE.

Physical Examination and History

A thorough history should investigate common complaints such as chest pain, dyspnea, fainting, palpitations, and fatigue. For patients experiencing palpitations, clinicians should ask about onset, frequency, and duration.

During the physical exam, clinicians should look for:

• Skin Condition: Pale, mottled, or cyanotic skin may indicate circulation problems, while flushed, warm skin may suggest other issues.
• Jugular Veins: Inspect for increased jugular pressure.
• Edema: Bilateral pitting edema may indicate right ventricular failure (RVF), whereas one-sided edema may suggest a localized blockage.
• Heart Sounds:
  • S1: Closure of tricuspid and mitral valves.
  • S2: Closure of pulmonary and aortic valves.
  • S3/S4: Abnormal sounds often associated with heart failure or myocardial infarction.
  • Murmurs: Caused by turbulent blood flow through irregular or constricted valves.

Vital Signs and Pulse Findings

Blood pressure (BP) and pulse assessments provide critical data regarding hemodynamic stability.

• Blood Pressure: Normal SBP is $<120$ and DBP is $<80$. In emergencies, an SBP $<90$ indicates hypotension or shock, while a widened pulse pressure can signal later stages of shock.
• Pulse Deficit: This is the difference between the apical pulse and the peripheral pulse.
• Pulsus Alternans: A beat-to-beat difference in the strength of the pulse.

Electrocardiogram (EKG) Interpretation

The EKG provides an electrical snapshot of the heart's conduction. A standard 12-lead EKG includes three limb leads, three augmented limb leads, and six precordial leads.

Key components of an EKG waveform include:

1. P-wave: Represents atrial depolarization.
2. PR-interval (PRI): The time required for the impulse to traverse the atria and AV junction (Normal: $0.12\text{--}0.20$ seconds).
3. QRS-complex: Represents ventricular depolarization (Normal: $<0.12$ seconds).
4. T-wave: Represents ventricular repolarization.

Exam Tip: When calculating heart rate using the 6-second method, count the number of QRS complexes in a 6-second strip and multiply by 10.

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Summary Table: Common Cardiac Rhythms