Basic Electrical Rhythm (BER) of the Gastrointestinal Tract

Definition

Key Characteristics

BER Frequency Along the GI Tract

BER Diagram

Modulation of the BER

• Acetylcholine (parasympathetic) - increases the number of spikes and muscle tension
• Membrane stretch (e.g., distension)
• GI hormones (e.g., gastrin, motilin)

• Norepinephrine / Epinephrine (sympathetic) - hyperpolarize the membrane, suppress spikes and reduce tension
• VIP (Vasoactive Intestinal Peptide)

Functional Roles

1. Peristalsis - BER waves in the stomach wall initiate mixing waves every 15-20 seconds, progressing toward the antrum. After vagotomy or transection, peristalsis becomes irregular and chaotic, highlighting the BER's role in coordination.
2. Segmentation (mixing contractions) - The maximum frequency of segmentation contractions in the small intestine is determined by BER frequency; contractions can only occur during the depolarizing phase of the waves.
3. Gastric emptying - BER-driven constrictor rings force antral contents toward the pylorus ("pyloric pump") and cause retroulsion (mixing).
4. Aborad propulsion gradient - The duodenum-to-ileum frequency gradient ensures net distal movement of luminal contents.

Tonic vs. Rhythmic Contractions

• Continuous repetitive spike potentials
• Hormonal partial depolarization
• Continuous Ca²⁺ entry independent of membrane potential changes

Clinical Relevance

• Hypothyroidism: BER frequency that generates peristaltic waves in the duodenum decreases, slowing small bowel transit and potentially causing constipation or myxedema megacolon. (Sleisenger & Fordtran's GI and Liver Disease)
• Diabetic gastroparesis / loss of ICC: Destruction or reduction of ICCs (as seen in diabetes) disrupts BER generation, leading to disordered motility.
• Post-vagotomy: Irregular, chaotic peristalsis results because the coordination of BER with neural input is lost.
• Migrating Motor Complex (MMC): During fasting, the MMC (initiated by motilin every ~90 min) superimposes on the BER to create organized sweeping contractions that clear the gut.

Achalasia Cardia

Definition

1. Impaired (failed) relaxation of the Lower Esophageal Sphincter (LES) with swallowing
2. Aperistalsis in the smooth muscle esophagus

Epidemiology

• Incidence: ~1-2 per 100,000 per year
• Peak age: 30-60 years; bimodal distribution (young adults + elderly)
• Equal sex distribution
• Can occur at any age, including children

Etiopathogenesis

Pathological Mechanism

• Mediate deglutitive inhibition (LES relaxation via NO and VIP)
• Coordinate sequential peristalsis in the esophageal body

• NO synthase (nitric oxide - the primary inhibitory neurotransmitter)
• VIP (Vasoactive Intestinal Peptide)-staining neurons at the gastroesophageal junction
• Partial preservation (or loss) of excitatory cholinergic neurons

Etiology

• Myenteric plexus infiltrate is predominantly cytotoxic T cells
• Antibodies against myenteric neurons detected in serum
• Association with specific HLA alleles
• Suspected trigger: HSV-1 (Herpes Simplex Virus type 1) - a chronic/latent infection
• The degree of ganglion cell loss parallels disease duration

Secondary Causes (Pseudoachalasia)

• Chagas disease (Trypanosoma cruzi) - also affects heart, brain, GI tract
• Malignancy (especially esophageal/GEJ carcinoma) - must be excluded in patients >60 years with short symptom duration and significant weight loss
• Allgrove (Triple A) Syndrome - achalasia + alacrima + adrenal insufficiency

Chicago Classification (HRM Subtypes)

Clinical Features

• Dysphagia is simultaneous to both solids and liquids from the onset (unlike mechanical obstruction = solids first)
• Onset is gradual, present for years before diagnosis
• Regurgitation is non-bilious, non-acid, mixed with copious mucoid saliva - may occur hours after eating
• "Heartburn" is from bacterial fermentation of retained food, not GERD - many patients are mistakenly treated with PPIs for years
• Chest pain may improve spontaneously over time unlike dysphagia

Eckardt Score (severity assessment)

Diagnosis

1. Barium Swallow

• First-line imaging; provides anatomic information
• Classic finding: "Bird-beak" deformity - dilated proximal esophagus tapering smoothly at the distal end/GEJ
• Other features: air-fluid level, slow emptying into stomach, tertiary contractions
• Can show sigmoid esophagus (advanced disease with massive dilatation + tortuosity) - important for surgical planning
• May be normal in ~30% of early cases

2. Endoscopy (EGD)

• Performed first in all patients with dysphagia to exclude malignancy (pseudoachalasia)
• Findings: retained food/saliva (~60%), esophagitis from food stasis, Candida infection
• Normal in ~40% of patients
• Classic feel: "pop" or resistance on passing scope through LES - scope passes with gentle pressure

3. High-Resolution Manometry (HRM) - Gold Standard

• Most sensitive test; establishes diagnosis AND subtype (Type I/II/III)
• Key findings:
  • Impaired LES relaxation - elevated integrated relaxation pressure (IRP >15 mmHg)
  • Aperistalsis in the esophageal body
  • Elevated LES resting pressure (often >45 mmHg)
• Essential for Chicago Classification subtyping

4. Functional Lumen Imaging Probe (FLIP)

• Newer complementary tool
• Uses impedance planimetry to assess esophageal compliance and distensibility
• Useful when manometry is non-classic but suspicion remains high

5. Ambulatory pH Monitoring

• Reserved for patients complaining of heartburn
• Distinguishes true GERD from food-fermentation pseudoreflux
• Achalasia shows: slow progressive pH drift below 4 (fermentation), NOT discrete reflux events

Treatment

Pharmacologic (Temporizing - Poor Efficacy)

• Calcium channel blockers: Sublingual nifedipine (30-40 mg/day before meals) - side effects (flushing, hypotension, headache) limit use
• Nitrates: Isosorbide dinitrate sublingually before meals - headache is common
• Sildenafil: Blocks PDE-5, raises cGMP, relaxes smooth muscle - short duration, high cost
• All reduce LES pressure modestly; best used as temporizing measures or in frail patients unfit for definitive therapy

Botulinum Toxin Injection (Endoscopic)

• Mechanism: Irreversibly inhibits ACh release from presynaptic cholinergic terminals
• Technique: 80-100 units injected in 4 quadrants at the LES
• Efficacy: 80% symptom relief at 1 month; drops to 40% at 12 months
• Not durable - effect reversed by new axon growth
• Repeated injections cause local fibrosis - increases technical difficulty and mucosal perforation risk if LHM later needed
• Reserved for: elderly/frail patients who are poor candidates for PD, LHM, or POEM

Pneumatic Dilation (PD)

• Disrupts circular muscle of LES by forceful balloon distension to ≥3 cm diameter
• Graded approach: start with 30 mm, escalate to 35 mm and 40 mm for persistent symptoms
• Rigiflex dilators - non-compliant cylindrical balloons passed over guidewire, positioned fluoroscopically
• Efficacy: ~86% success at 2 years; 82% at 5 years (comparable to LHM)
• ~25% of patients require repeat dilations
• Risk of perforation: ~1% (comparable to LHM)
• Best for Type II achalasia (100% efficacy in some series)
• Poor response predictors: age <40, male sex, Type I or III, large esophageal diameter, post-dilation LES pressure >10 mmHg

Laparoscopic Heller Myotomy (LHM)

• Surgical division of the circular muscle fibers of the LES and cardia (6 cm on esophagus, 2-3 cm onto stomach)
• Always combined with partial fundoplication (Dor or Toupet) to prevent post-op GERD
• Efficacy: ~90% overall; best in Type II, lower in Type I and III
• Durable results; 5-year success ~84%
• Risk of perforation ~1%; post-op GERD ~10-15%
• Superior to PD for Type III achalasia (~86% vs. ~40%)

POEM - Per Oral Endoscopic Myotomy

• Endoscopic technique pioneered by Dr. Haruhiro Inoue (2008)
• Submucosal tunnel created endoscopically; circular muscle fibers divided from inside
• Advantages over LHM: no external incisions, longer myotomy possible (especially useful for Type III), shorter recovery
• Particularly effective for Type III (spastic) achalasia because a longer myotomy can be extended proximally
• Main drawback: higher rate of post-procedural GERD (no fundoplication routinely added)
• Recent meta-analysis (2024) shows comparable efficacy to LHM with fundoplication; POEM has lower dysphagia recurrence but higher reflux rates

Esophagectomy

• Last resort for end-stage/sigmoid achalasia that has failed all other treatments
• Also indicated if malignancy cannot be excluded

Complications

Summary: Treatment Algorithm

Achalasia diagnosed (HRM subtyped)
        |
        ├── Type I or II → Pneumatic Dilation (first-line) OR LHM
        |      └── Type II specifically: PD ~100% effective
        |
        ├── Type III (spastic) → LHM or POEM preferred (PD inferior)
        |
        ├── Poor surgical candidate / elderly frail → Botox injection
        |
        └── End-stage sigmoid esophagus → Esophagectomy