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Effect of CCBs on Pulse Rate

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1. Dihydropyridines (DHPs) - Increase Pulse Rate

• DHPs bind preferentially to L-type calcium channels in vascular smooth muscle, causing potent peripheral arterial vasodilation with minimal direct cardiac effect.
• The sudden drop in systemic vascular resistance triggers baroreceptor-mediated reflex sympathetic activation.
• This reflex leads to increased heart rate (reflex tachycardia) and maintenance or even increase in cardiac output.

• Reflex sympathetic activation with slight tachycardia maintains or increases cardiac output in most patients.
• Short-acting nifedipine produces the most pronounced reflex tachycardia and is associated with increased cardiovascular risk - it should NOT be used for hypertension unless the patient is already on a beta-blocker.
• Long-acting formulations (e.g., amlodipine) cause less pronounced tachycardia due to a slower, more gradual onset of vasodilation.
• In overdose, as toxicity becomes severe, tachycardia may eventually transition to bradycardia.

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2. Non-Dihydropyridines (Non-DHPs) - Decrease Pulse Rate

• Both verapamil and diltiazem block L-type calcium channels in the myocardium AND vascular smooth muscle.
• This depresses SA nodal automaticity (negative chronotropy) and AV nodal conduction (negative dromotropy).
• Net effect: slowed heart rate (bradycardia) and reduced cardiac output.

• Verapamil has the greatest cardiac depressant effect and causes the most heart rate slowing.
• Diltiazem has intermediate effects - less cardiac depression than verapamil, less vasodilation than DHPs.
• Both are used for rate control in atrial fibrillation and SVT precisely because of their AV nodal slowing effect.
• Contraindicated in combination with beta-blockers due to synergistic depression of SA/AV nodal conduction and risk of complete heart block.
• Contraindicated in heart failure with reduced ejection fraction (HFrEF).

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Summary Table

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Clinical Application

• When a patient on a dihydropyridine has bothersome palpitations or tachycardia, a beta-blocker is often added - this is why the combination of DHP + beta-blocker is a standard angina regimen.
• Diltiazem is the preferred non-DHP CCB in ACS (non-ST elevation) for patients who cannot tolerate beta-blockers, as it slows heart rate and reduces ischemia.
• In overdose, all CCBs can eventually cause bradycardia, AV block, and cardiovascular collapse, regardless of subclass.

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Approach to Bilateral Lower Limb Swelling

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Pathophysiology of Edema

1. Increased capillary hydrostatic pressure - e.g., heart failure, venous obstruction
2. Decreased plasma oncotic pressure - e.g., hypoalbuminemia (liver disease, nephrotic syndrome, malnutrition)
3. Increased capillary permeability - e.g., inflammation, allergy
4. Increased interstitial oncotic pressure - e.g., myxedema (hypothyroidism)
5. Lymphatic obstruction - e.g., lymphedema

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Step 1: Determine Distribution (Pivotal Point)

"Although there are some local diseases that can present with bilateral leg edema, the first step in such patients is always to look for systemic causes." - Symptom to Diagnosis, 4th Ed.

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Differential Diagnosis of Bilateral Lower Limb Swelling

A. Systemic Causes (most common)

1. Cardiovascular

2. Hepatic

• Cirrhosis - hypoalbuminemia + portal hypertension
• Key clues: jaundice, spider angiomata, gynecomastia, splenomegaly, ascites, flat/low JVP (distinguishes from cardiac)

3. Renal

• Chronic kidney disease - sodium and water retention
• Nephrotic syndrome - massive proteinuria (>3.5 g/day), hypoalbuminemia, hyperlipidemia; periorbital edema is characteristic
• Key test: urine albumin/creatinine ratio, BUN/creatinine

4. Nutritional / GI

• Malnutrition, malabsorption, protein-losing enteropathy
• Mechanism: hypoalbuminemia reducing plasma oncotic pressure

5. Endocrine

• Hypothyroidism (Myxedema) - non-pitting edema from increased interstitial glycosaminoglycans
• Note: true hypothyroid edema is typically non-pitting, so it will NOT respond to diuretics

6. Medications (common and often missed)

7. Hematologic

• Severe anemia - high-output state with peripheral vasodilation

B. Local / Vascular Causes

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Step 2: History

• Onset and duration - acute (DVT, acute HF) vs. chronic (venous insufficiency, cirrhosis)
• Diurnal variation - worse by evening = venous/gravitational; worse in morning = cardiac/renal
• Associated symptoms:
  • Dyspnea, orthopnea, PND → Heart failure
  • Abdominal distension, jaundice → Cirrhosis
  • Frothy urine → Nephrotic syndrome
  • Fatigue, cold intolerance, constipation → Hypothyroidism
• Drug history - especially CCBs, steroids, NSAIDs, thiazolidinediones
• Risk factors - alcohol use, viral hepatitis exposure, malignancy, immobility, cardiac disease, diabetes, hypertension
• Family history - lymphedema (Milroy disease, Meige disease)

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Step 3: Physical Examination

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Step 4: Investigations

First-line (all patients)

Second-line (selected patients)

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Diagnostic Flowchart

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Step 5: Management Principles (cause-directed)

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• Always check bilateral vs. unilateral first - bilateral = systemic until proven otherwise.
• JVP is one of the most useful bedside signs to distinguish cardiac (elevated) from hepatic/renal (normal or low) causes.
• Non-pitting edema = lymphedema or myxedema - diuretics will not help.
• A thorough drug history will identify a reversible cause in many patients.
• When no systemic cause is found after workup, consider venous insufficiency, lymphedema, or lipedema.