Electrical Stimulation & Circulation - PG Level

1. Basic Concept

• Vagal / autonomic stimulation (physiological)
• Transcutaneous electrical nerve stimulation (TENS)
• Cardiac pacing (temporary and permanent)
• Cardioversion and defibrillation
• Implantable devices (ICD, CRT)
• Spinal cord stimulation for ischemic pain

2. Physiological Basis: The Electrical Heart

• The SA node fires intrinsically at 60-100 bpm
• Sympathetic input (epinephrine, norepinephrine) increases rate via adrenergic receptors
• Parasympathetic (vagal) input slows the SA node by reducing the pacemaker depolarization rate and delays AV nodal conduction
• Cardiac output (CO) = Heart Rate (HR) × Stroke Volume (SV); circulation depends critically on maintaining this

"The discharge rate of the SA node is usually modulated by a balance of input from the sympathetic and parasympathetic nerves (i.e., the autonomic nervous system)." - Roberts and Hedges' Clinical Procedures in Emergency Medicine

3. Vagal (Parasympathetic) Electrical Effects on Circulation

"Vagal stimulation results in slowing of electrical activity, examples being termination of an SVT, slowing of the ventricular rate of AF (via the AV node), or simply producing a sinus bradycardia (via the SA node)." - Roberts and Hedges' Clinical Procedures in Emergency Medicine

4. Cardiac Pacing

A. Temporary Pacing

• Transcutaneous (external): Quickest option; electrodes placed on chest wall; uncomfortable due to pectoral muscle stimulation; ~20% of patients fail to achieve capture
• Transvenous: Lead placed percutaneously via internal jugular or subclavian into the right ventricular apex; more reliable

• Asystolic cardiac arrest
• Symptomatic bradycardia (hemodynamic compromise)
• Torsades de pointes suppression (rate kept 85-100 bpm until offending drug cleared)
• High-degree AV block in acute MI
• Bradycardia during interventional/surgical cardiac procedures
• Overdrive pacing to terminate sustained SVT or VT

• Set pacemaker rate ~10 bpm below intrinsic rate
• Gradually increase sensitivity (clockwise) until oversensing - this is too sensitive
• Reduce back to halfway between oversensing point and sensing threshold
• Final setting set at 2 mA above the threshold at which capture is lost
• Risk of "pulseless electrical activity" (PEA/electromechanical dissociation) must be recognized if spikes and LBBB pattern are present but no pulse

B. Permanent Pacemaker

• Pulse generator (battery + circuitry)
• 1-3 leads placed transvenously (axillary/subclavian/cephalic vein)
• Atrial lead: right atrial appendage
• Ventricular lead: RV apex, RV septum, or outflow tract ("active fixation" with helical screw)

"Pacemakers are implanted either to alleviate symptoms caused by bradycardia or to prevent severe symptoms in patients in whom symptomatic bradycardia is likely to develop." - Goldman-Cecil Medicine

5. Cardioversion & Defibrillation

Defibrillation

"Defibrillation is the therapeutic use of electricity in cardiac arrest to depolarize the entire myocardium to eliminate ventricular fibrillation or nonperfusing ventricular tachycardia so that coordinated contractions can resume." - Tintinalli's Emergency Medicine

• Mechanism: Non-synchronized shock depolarizes all myocardial cells simultaneously, rendering them refractory and allowing the SA node (or highest automaticity focus) to re-establish sinus rhythm
• Energy: 360 J (monophasic) or 200 J (biphasic)
• Indication: VF, pulseless VT only
• Defibrillation is NOT for asystole (it is not "jumpstarting the heart")

Cardioversion

• Mechanism: Electrical discharge synchronized to the R wave of the QRS complex (avoids the vulnerable T-wave period, which can trigger VF)
• Purpose: Convert tachyarrhythmias - AF, atrial flutter, hemodynamically unstable SVT, VT with pulse
• Key distinction from defibrillation: Synchronization to QRS prevents inducing VF

• Digitalis toxicity (absolute)
• Left atrial/appendage thrombus (unless TEE negative)
• Sick sinus syndrome (pacemaker must be in situ first)
• AF >48 hours without adequate anticoagulation (5% thromboembolic risk in first 2 weeks post-cardioversion)
• Large left atrial diameter (>4.5 cm) - low chance of maintaining sinus rhythm

Atrial Fibrillation Treatment (Guyton and Hall)

6. Effect of Electrical Stimulation on Peripheral Circulation

TENS (Transcutaneous Electrical Nerve Stimulation)

• Modulates pain via dorsal horn mechanisms (gate control), but also has secondary vasomotor effects
• Evidence for direct circulatory benefit is limited

Spinal Cord Stimulation (SCS)

• Electrode placed epidurally to stimulate dorsal columns
• Improves ischemic limb blood flow in peripheral vascular disease
• Strongest evidence: complex regional pain syndrome, ischemic pain (Goldman-Cecil Medicine)
• Conventional, high-frequency, and burst stimulation all effective; mechanism includes sympathetic inhibition causing vasodilation

Hemodynamic Effects of Tachyarrhythmias (and why electrical therapy restores circulation)

"CO begins to drop, mean arterial blood pressure (MAP) will decrease and cause hypoperfusion of the brain and other peripheral tissue (MAP = CO × TPR)." - Roberts and Hedges'

7. Implantable Cardioverter Defibrillator (ICD)

1. Antitachycardia pacing (ATP) - attempts to interrupt VT by pacing
2. Low-energy cardioversion
3. High-energy defibrillation
4. Bradycardic backup pacing

8. Summary Table

• Goldman-Cecil Medicine (International Edition), 2-Volume Set
• Roberts and Hedges' Clinical Procedures in Emergency Medicine
• Pfenninger and Fowler's Procedures for Primary Care, 3rd ed.
• Guyton and Hall Textbook of Medical Physiology
• Tintinalli's Emergency Medicine: A Comprehensive Study Guide
• Braunwald's Heart Disease, 15th ed.

Electrical Stimulation & Circulation

Basic MPT Level

1. What Is Electrical Stimulation?

2. How Electricity Affects Circulation - Basic Mechanisms

a) Direct Muscle Contraction (Neuromuscular Electrical Stimulation - NMES)

• The current depolarizes motor nerves → causes rhythmic muscle contractions
• Contracting muscles squeeze surrounding veins → acts like a muscle pump
• This increases venous return to the heart
• Important in immobilized or post-surgical patients to prevent DVT (deep vein thrombosis)

b) Axon Reflex / Vasodilation

• Sensory nerve stimulation triggers release of neuropeptides (substance P, CGRP)
• These cause arteriolar vasodilation and increased local blood flow
• Known as neurogenic vasodilation

c) Sympathetic Inhibition

• Certain ES modalities (e.g., TENS, SCS) inhibit sympathetic vasoconstriction
• Result: blood vessels relax → peripheral circulation improves

3. Modalities Used in Physiotherapy & Their Circulatory Effects

A. TENS (Transcutaneous Electrical Nerve Stimulation)

• Applied through skin electrodes
• Conventional TENS (high frequency, low intensity): primarily pain relief via gate control; mild local vasodilation via axon reflex
• Acupuncture-like TENS (low frequency, high intensity): stronger vasodilation via endorphin and neuropeptide release
• Clinical use: Ischemic pain, complex regional pain syndrome (CRPS), peripheral vascular disease pain
• Evidence supports short-term benefit for neuropathic pain

B. NMES / Faradic Stimulation

• Stimulates motor nerves to produce rhythmic muscle contractions
• Most important circulatory effect: augments venous return via the calf muscle pump
• Used post-surgery, in ICU patients, and in paralyzed limbs to prevent venous stasis and DVT
• Also maintains muscle bulk → preserves pumping capacity

C. Interferential Therapy (IFT)

• Two medium-frequency currents (typically 4000 Hz) cross in tissue, creating a low-frequency interference pattern (1-150 Hz) at depth
• Causes deeper muscle contractions than TENS
• Promotes increased local circulation, reduces edema, accelerates tissue healing
• Preferred when deeper penetration is needed (e.g., hip, shoulder girdle)

D. Galvanic Current (Direct Current)

• Anode (+): vasoconstriction, used to reduce acute bleeding/edema
• Cathode (-): vasodilation, increases blood flow to chronic ischemic areas
• Iontophoresis uses DC to drive anti-inflammatory drugs (e.g., dexamethasone) into tissue via local circulation enhancement

4. Electrical Stimulation & Venous Return - Key Concept for MPT

• Calf muscle contraction → compresses deep veins → propels blood proximally
• Calf muscle relaxation → venous valves prevent reflux → veins refill from superficial system

• Calf muscle pump fails → venous stasis → risk of DVT and pulmonary embolism

• Mimics the muscle pump action
• Maintains venous flow velocity
• Reduces stasis
• This is the primary circulation-related use of ES in physiotherapy

5. Spinal Cord Stimulation (SCS) & Peripheral Circulation

• Epidural electrodes at posterior dorsal columns
• Indicated for: peripheral vascular disease ischemic pain, CRPS, neuropathic limb pain
• Mechanism: sympathetic inhibition → arteriolar vasodilation → improved peripheral blood flow → reduced ischemic pain and tissue damage
• Effective for ischemic lower extremity pain due to peripheral vascular disease
• Used when conservative measures fail; 5-7 day trial first before permanent implant

6. Electrical Stimulation in Wound Healing & Microcirculation

• Promotes angiogenesis (new blood vessel formation) in chronic wounds
• Galvanic stimulation attracts macrophages, fibroblasts, and neutrophils by galvanotaxis
• Increases capillary density in wound beds
• Used in pressure ulcers, diabetic foot ulcers, and non-healing surgical wounds

7. Contraindications Related to Circulation

8. Quick Summary Table

Key Points to Remember (MPT Exam Focus)

1. NMES + calf muscle = venous pump - most tested circulatory application in physiotherapy
2. TENS causes vasodilation via axon reflex (sensory nerve stimulation → neuropeptides)
3. Cathode causes vasodilation; anode causes vasoconstriction in DC application
4. SCS improves peripheral circulation in PVD via sympathetic inhibition
5. DVT is an absolute contraindication - never apply ES over a known thrombus
6. IFT penetrates deeper than TENS for circulation effects in deeper structures

CRPS: Mechanism & How Electrical Stimulation Improves Circulation

Part 1: What Is CRPS?

Part 2: Clinical Features & Stages

Three Stages of Progression:

• Burning, throbbing pain localized to one limb
• Mild edema, increased skin temperature (warm, red)
• Vasomotor instability

• Edema spreads, skin thickens, muscle wasting begins
• Skin becomes cool, mottled
• Joint stiffness increases

• Irreversible trophic changes - waxy skin, brittle nails
• Severe limb contractures, flexor deformity
• Marked osteoporosis on X-ray
• Cold, cyanotic limb, severely impaired circulation

Part 3: Pathophysiology - The Mechanism of CRPS

Mechanism 1: Peripheral Sensitization & Neurogenic Inflammation

• Substance P and CGRP (Calcitonin Gene-Related Peptide): Cause neurogenic inflammation - vasodilation, plasma extravasation, mast cell degranulation
• Elevated CGRP levels are found systemically in CRPS patients
• These mediators sensitize peripheral nociceptors → hyperalgesia and allodynia
• Neurogenic edema forms from increased vascular permeability

"Increased systemic calcitonin gene-related peptide (CGRP) levels may contribute to neurogenic inflammation, edema, vasodilatation, and increased sweating. Elevated neuropeptide concentrations may lead to pain and hyperalgesia." - Bradley and Daroff's Neurology

Mechanism 2: Sympathetic-Afferent Coupling (Key Circulatory Mechanism)

1. Peripheral injury → upregulation of alpha-adrenergic receptors on nociceptors and blood vessel walls
2. Functional coupling develops between sympathetic efferent fibers and sensory afferent fibers
3. Norepinephrine from sympathetic terminals now directly excites pain fibers (sympathetically maintained pain)
4. Paradoxical circulatory changes:
   • Early: decreased sympathetic outflow → vasodilation → warm, red limb
   • Late: catecholamine hypersensitivity of upregulated alpha receptors → intense vasoconstriction → cold, cyanotic, ischemic limb

"There is decreased sympathetic outflow to the affected limb and autonomic manifestations previously ascribed to sympathetic overactivity are now thought to be due to catecholamine hypersensitivity." - Bradley and Daroff's Neurology

Mechanism 3: Central Sensitization

• Wind-up in dorsal horn → spinal cord sensitization
• Wide dynamic range (WDR) neurons become hyperexcitable
• Cortical reorganization in the primary somatosensory cortex (S1) - the affected body part representation shrinks or reorganizes
• Disinhibition of motor cortex → tremor, dystonia
• Brainstem and thalamic involvement → widespread pain spread (limb-to-limb spread of CRPS)
• Immunological contributions: Altered HLA expression, cytokines, interleukins → maintain inflammatory and edematous state

Mechanism 4: Immune-Inflammatory Component

• Autoantibodies against adrenergic and muscarinic receptors have been found in CRPS patients
• Pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) in local tissue
• These perpetuate neurogenic inflammation and microvascular changes

Part 4: Circulatory Disturbances in CRPS - Summary

Part 5: How Electrical Stimulation Improves Circulation in CRPS

Pathway 1: TENS - Inhibition of Sympathetic Vasoconstriction

• Activates large Aβ sensory fibers → dorsal horn gate control
• Reduces dorsal horn hyperexcitability → decreases central sensitization
• Diminishes sympathetic efferent output from the spinal cord → reduces vasoconstriction
• Result: improved arteriolar dilation and skin blood flow

• Activates Aδ fibers → hypothalamus releases endorphins and enkephalins
• Also triggers axon reflex → antidromic release of CGRP from C-fiber terminals
• CGRP is a potent vasodilator → direct arteriolar dilation
• Result: lasting improvement in skin microcirculation

Pathway 2: Spinal Cord Stimulation (SCS) - Most Evidence-Based ES for CRPS

1. Epidural electrode placed in posterior epidural space (usually T8-T10 for lower limb CRPS)
2. Dorsal column stimulation → activates large myelinated Aβ fibers
3. Antidromic activation reaches peripheral sensory terminals → releases vasodilatory neuropeptides (CGRP, VIP)
4. Inhibits sympathetic preganglionic neurons in the intermediolateral column of the spinal cord → reduces norepinephrine release → reduces alpha-adrenergic vasoconstriction
5. Supraspinal effects: Activates descending inhibitory pathways (serotonergic, noradrenergic) that modulate sympathetic tone
6. Net effect: sustained vasodilation of the affected limb's blood vessels, increased skin perfusion, reduced ischemic pain

"Spinal cord stimulation (SCS) may be effective for neuropathic pain, including sympathetically mediated pain... ischemic lower extremity pain due to peripheral vascular disease." - Morgan & Mikhail's Clinical Anesthesiology

• 5-7 day external trial → if >50% pain relief, proceed to permanent implant
• Paresthesia should cover the painful area
• Effective even for full-body CRPS spread
• "Unfortunately, the effectiveness of the technique decreases with time in some patients"

Pathway 3: NMES - Muscle Pump to Reduce Edema

• NMES causes rhythmic calf/limb muscle contractions
• Acts as a mechanical venous pump → clears edema fluid
• Reduces venous hypertension → improves capillary filling
• Allows better arterial inflow to the tissue

Pathway 4: Interferential Therapy (IFT) - Deep Tissue Circulation

• Medium-frequency carrier (4000 Hz) passes through skin easily
• Beat frequency (1-150 Hz) at the crossover point causes:
  • Vasodilation via local axon reflex
  • Rhythmic deep muscle contractions
  • Reduction of edema by improving lymphatic drainage
• Used when CRPS involves deep joints (shoulder, hip) where TENS penetration is insufficient

Pathway 5: Dorsal Root Ganglion (DRG) Stimulation

• Electrode placed at the DRG level
• More targeted than SCS - only covers the specific dermatome affected
• Modulates afferent signaling directly at the DRG → reduces nociceptor sensitization → decreases sympathetic reflex vasoconstriction
• Shown to be an effective alternative to SCS for CRPS and improves tolerance for physical therapy

"Dorsal root ganglion (DRG) stimulation has been shown to be an effective therapy and alternative to SCS to help treat CRPS in the lower extremities." - Morgan & Mikhail's Clinical Anesthesiology

Part 6: Summary Diagram - CRPS Mechanism & ES Intervention Points

TISSUE INJURY
      ↓
C-fiber / Aδ activation
      ↓
Neuropeptide release (Substance P, CGRP)
  → Neurogenic inflammation → Edema       ← [TENS reduces via gate control]
      ↓
Peripheral sensitization → Allodynia / Hyperalgesia
      ↓
Spinal cord sensitization (central sensitization)
  → WDR hyperexcitability                 ← [SCS interrupts dorsal horn]
      ↓
Sympathetic-afferent coupling
  → Upregulated α-adrenergic receptors    ← [SCS inhibits sympathetic outflow]
      ↓
Catecholamine hypersensitivity
  → Vasoconstriction → Ischemia → Cold limb ← [TENS/SCS: vasodilation]
      ↓
Disuse atrophy + venous stasis
  → Edema, trophic changes                ← [NMES: muscle pump, reduces edema]

Part 7: Quick Revision Table for MPT

1. CRPS mechanism = peripheral sensitization + central sensitization + sympathetic-afferent coupling + immune inflammation
2. The cold phase of CRPS (late stage) is due to catecholamine hypersensitivity of upregulated alpha receptors, NOT increased sympathetic outflow
3. SCS has the strongest evidence for CRPS among all ES modalities
4. ES improves CRPS circulation primarily via sympathetic inhibition → vasodilation
5. CGRP is the key vasodilatory neuropeptide involved in both the CRPS pathology and the ES therapeutic response
6. Budapest Criteria require symptoms in ≥3 domains + signs in ≥2 domains