Barium esophagram demonstrating each type of achalasia. Type 1 achalasia (a) with dilated esophagus and bird’s beak appearance at the lower esophageal sphincter (LES). Type II achalasia (b) with non-dilated esophagus but narrowing at the LES. Type III achalasia (c) with corkscrew appearance from spasm in the esophageal body 
While EGD and barium swallow are mandatory for the work up of achalasia, manometry is the gold standard diagnostic test . Providers must have a thorough working knowledge of manometry in order to diagnose achalasia, classify patients according to the Chicago classification, and differentiate achalasia from other motility disorders such as diffuse esophageal spasm and jackhammer esophagus .
Manometry became possible in 1970s when Wyle Jerry Dodds and Ron Arndorger developed the first high-fidelity manometry system. In the 1990s, Ray Clouse and his colleagues developed high-resolution manometry (HRM) which included several modifications allowing for capture of the motor function from the upper esophageal sphincter (UES) and the lower esophageal sphincter (LES) simultaneously with each swallow, giving us a complete spatial and temporal depiction of the esophageal motor function for the first time. HMR manometry also converts the pressure data to a topographical plot providing a pictoral representation of pressure waves called esophageal pressure topography (EPT) . Colors are assigned to pressures, with high pressures represented by warmer colors (reds and yellows) and low pressures by cool colors (blues and greens) (Fig. 6.2).
Comparing conventional recordings of manometric pressure with the Clouse plot or esophageal pressure topography (EPT). Conventional manometry tracings came from catheters made with pressure sensors spaced at relatively wide intervals, usually at 3- to 5-cm. (a) Is a representation of conventional manometric recordings. (b) Is a representation of the widely adopted Clouse plot 
High-Resolution Manometry Analysis
Analysis of HRM starts by noting the pressures of the upper and lower esophageal sphincters at rest. Then the pressure waves are analyzed during ten wet swallows taking note of three important characteristics: (1) The function of the lower esophageal sphincters during bolus transit, (2) Peristaltic integrity of the esophageal body, and (3) Distinguishing pressure patterns .
In order to evaluate the resting characteristics of the esophageal sphincters, a 30-s period during which no swallow occurs must be observed. The upper and lower esophageal sphincters are identified as zones of higher pressure depicted on the EPT as horizontal bands of color, as seen in Fig. 6.3. The location of the LES relative to the pressure inversion point (PIP) can indicate the presence of a hiatal hernia. The PIP identifies where the diaphragm separates the chest from the abdomen and usually is found close to the LES. Spatial separation of the LES and PIP in the EPT indicates a hiatal hernia .
Pressures recorded from the esophagogastric junction (EGJ) are a composite of tonic lower esophageal sphincter (LES) contraction (double asterisks) and cyclical crural diaphragm contraction with inspiration (asterisk). During inspiration, pressure decreases in the thoracic cavity, and during expiration it increases. The opposite is true in the abdominal cavity. The point at which pressure across the EGJ during inspiration becomes negative relative to intra-abdominal pressure is called the respiratory or pressure inversion point (PIP). It indicates the location of the crural diaphragm. The red arrowhead denotes the location of the PIP. The top panel is an example of a normal (Type I) EGJ in which the LES and crural diaphragm are coincident. In the middle panel, there is a small spatial separation (<2 cm) of the diaphragm from the LES, indicating a small hiatal hernia (Type II EGJ). In the bottom panel, there is a large spatial separation (>2 cm) between the crural diaphragm and LES, indicating the presence of a large hiatal hernia (Type III EGJ). I inspiration, E expiration 
Next, the manometry is evaluated during a series of at least ten wet swallows (5 mL water) to observe the function of the lower esophageal sphincter (LES). The integrated residual pressure (IRP) is a tool developed to measure the resistance to bolus movement across the EGJ. IRP greater than 15 mmHg indicates outflow obstruction at the GEJ, which can be due to achalasia or mechanical obstructions such as neoplasms or strictures . Differentiation between achalasia and mechanical obstruction is determined by non-peristaltic esophageal pressurization patterns which indicate achalasia .
The peristaltic integrity is determined by the 20 mmHg isobaric contour line. It is a black line drawn around all parts of the EPT where the pressure is 20 mmHg. This threshold value of 20 mmHg is chosen because this is the peristaltic pressure required for normal bolus transit when the EGJ is functioning normally . Peristaltic integrity is assessed by measuring gaps in the 20 mmHg contour line along the length of the esophagus.
The third step in analyzing EPT is to determine if there is a pressurization pattern. Pressurization is recognized as isobaric pressure along varying lengths of esophagus. It indicates bolus entrapment. Once all the swallows are analyzed with the tools described above, the data are used in the Chicago classification to make a diagnosis (Table 6.1).
Esophageal pressure topography metrics utilized in the Chicago classification 
Pressure topography metrics
Integrated relaxation pressure (mmHg)
Mean EGJ pressure measured with an electronic equivalent of a sleeve sensor for four contiguous or non-contiguous seconds of relaxation in the 10-s window following deglutitive UES relaxation
Distal contractile integral (mmHg s cm)
Amplitude × duration × length (mmHg s cm) of the distal esophageal contraction >20 mmHg from proximal (P) to distal (D) pressure troughs
Contractile deceleration point [(CDP) (time, position)]
The inflection point along the 30 mmHg isobaric contour where propagation velocity slows demarcating the tubular esophagus from the phrenic ampulla
Contractile front velocity (cm s−1)
Slope of the tangent approximating the 30 mmHg isobaric contour between P and the CDP
Distal latency (s)
Interval between UES relaxation and the CDP
Peristaltic breaks (cm)
Gaps in the 20 mmHg isobaric contour of the peristaltic contraction between the UES and EGJ, measured in axial length
The Chicago Classification
The Chicago classification was derived using the ManoScan™ (Sierra Scientific Instruments, Los Angeles, CA, USA) HMR system. It is important to note that measurements may vary based on HMR transducer used. The Chicago classification is indicated to classify primary motility disorders. It is not intended for post-surgical patients as procedures such as the lap band, fundoplication, and even balloon dilation alter manometry characteristics . The Chicago classification uses five main metrics to classify motility disorders: (1) The integrated relaxation pressure (IRP), (2) Distal Latency (DL), (3) contractile deceleration point (CDP), (4) Peristaltic Breaks, and (5) Distal contractile Integral (DCI) 
The integrated relaxation pressure is a tool to measure the resistance to bolus movement across the EGJ. The HMR catheter is positioned to straddle the LES and measure pressures over a 6 cm segment. It calculates the maximum pressure along the 6 cm segment at each time point within a 10-s window. The 4-s IRP algorithm takes these pressures and averages the lowest pressures of any 4 s within the 10-s timeframe . IRP greater than 15 mmHg indicates outflow obstruction at the GEJ .
Distal latency is a measurement of the time from start of swallow-induced UES opening to time of arrival of the esophageal contraction to the contractile deceleration point . The lower limit of normal is 4.5 s.
The contractile deceleration point is defined as the inflection point along the 20 mmHg isobaric contour line where the propagation velocity slows demarcating the time at which esophageal peristalsis terminates and the LES begins.
Peristaltic breaks are gaps in the 20 mmHg isobaric contour of the peristaltic contraction between the UES and GEJ. According to the Chicago classification, small defects measure 2–5 cm and large defects are >5 cm 
Distal Contractile Integral is used to measure the robustness of peristaltic contraction in the smooth muscle esophagus. The DCI integrates pressure, distance, and time along the esophagus to describe the mean contractile amplitude of the small bowel esophagus, the length over which the contraction propagates, and the duration of the contraction. DCI >8000 is seen in symptomatic patients (Fig. 6.4).
Evaluation of peristalsis with the distal latency and contraction front velocity. (a) Distal esophageal spasm is characterized by normal lower esophageal sphincter relaxation and a short distal latency (<4.5 s). It is the arrival of the swallow-induced contraction in the distal esophagus too rapidly, producing a simultaneous contraction 
The Chicago Classification can help classify esophageal motor abnormalities into four general groupings: Achalasia, esophageal outlet obstruction, abnormalities of esophageal motor function, and boarder line abnormalities, which are usually seen in asymptomatic patients.
Achalasia is defined by failure of normal peristalsis and inadequate lower esophageal sphincter relaxation (integrated residual pressure (IRP) greater than normal 15 mmHg). This disorder is then subclassified into three subtypes based on analysis of esophageal pressure patterns, defined by the Chicago classification . All types have failure of LES relaxation (IRP >15 mmHg), but have different pressurization patterns. Type I achalasia has no appreciable motor activity, type II is characterized by abnormal peristalsis with pan-esophageal pressurization following at least 20% of wet swallows, and type III exhibits premature spastic contractions with at least 20% of wet swallows . The EPT patterns are shown in figure below. These subtypes account for the variability seen on barium swallow studies demonstrating the different pattern of achalasia as seen in Fig. 6.1 (Fig. 6.5).
Type I achalasia has no appreciable motor activity, type II is characterized by abnormal peristalsis with pan-esophageal pressurization following at least 20% of wet swallows, and type III exhibits premature spastic contractions with at least 20% of wet swallows 
It has been shown that patients with achalasia have different responses to therapy depending on their subtype. Type II is the strongest predictor of treatment response and type III is a negative predictor of response . In the study by Pandolfino et al., type 1 patients underwent a mean number of 1.6 therapeutic interventions (botox, pneumatic dilation, or laparoscopic Heller myotomy) during a mean follow-up period of 19 months and experienced a response rate of 56% after most recent therapy. Interestingly, these patients did significantly better with LHM than balloon dilation or botox. Type II patients underwent an average of 1.2 interventions during a mean follow-up of 20 months and had an excellent response to all three interventions with 96% success. Type III patients had the worst response to therapy despite having significantly greater number of therapeutic interventions during a mean follow-up period of 20 months. These patients had a 29% response rate. Although POEM was not available and therefore not included in this study, we can extrapolate that type I and type II achalasia patients may have better results than type III to POEM as well.
It is just as important to determine what is not achalasia as it is to recognize achalasia on manometry. Esophageal junction outflow obstruction is characterized by failed or incomplete opening of the EGJ, but is distinguished from achalasia by retained peristalsis in the smooth muscle esophagus . Pressurization of the esophagus occurs due to the entrapment of the swallowed bolus between unyielding EGJ and peristaltic contractions. This pattern of manometry should trigger further evaluation with endoscopy to look for mechanical obstruction. When no mechanical obstruction is found, this EPT pattern might indicate a variant of achalasia, which often responds to achalasia treatment .
Esophageal Motor Dysfunctions
Diffuse esophageal spasm is an uncommon motor dysfunction characterized by at least 20% of wet swallows producing a short Distal Latency (DL) <4.5 s with normal IRP. A short DL indicates early arrival of the esophageal contraction to the distal esophagus depicting spasm . This differs from type III achalasia where the DL is also low but the IRP is high.
Hypertensive LES can overlap with other motility disorders, but the hallmark is LES pressures greater than 35 mmHg and failure or relaxation below IRP of 15 mmHg. This leads to a degree of outflow obstruction which can lead to high distal esophageal pressures or even spasms .
Nutcracker Esophagus is characterized by prolonged, hypertensive contractions in the context of normal propagation of the swallow waveform. DCI is over 5000 and the pressure wave shows vigorous contractions, with normal DL and IRB .
Jackhammer esophagus is represented by high mean contraction amplitude of the smooth muscle esophagus over the length the contraction propagates. This is measured by Distal contractile integral (DCI). DCI >8000 represents symptomatic contractile strength or jackhammer esophagus. DCI <5000 is associated with asymptomatic controls  (Table 6.2).
The Chicago classification of esophageal motility 
Type I achalasia
Classic achalasia: mean IRP > upper limit of normal, 100% failed peristalsis
Type II achalasia
Achalasia with esophageal compression: mean IRP > upper limit of normal, no normal peristalsis, pan-esophageal pressurization with ≥20% of swallows
Type III achalasia
Mean IRP > upper limit of normal, no normal peristalsis, preserved fragments of distal peristalsis or premature (spastic) contractions with ≥20% of swallows
EGJ output obstruction
Mean IRP > upper limit of normal, some instances of intact peristalsis or weak peristalsis with small breaks such that the criteria for achalasia are not met
[Patterns not observed in normal individuals]
Distal esophageal spasm
Normal mean IRP, ≥20% premature contractions
Hypercontractile esophagus (Jackhammer esophagus)
At least one swallow DCI > 8000 mmHg s cm with single peaked or multipeaked contraction
Indications for POEM were initially limited to achalasia type I and II ; however, since then modifications of the technique have been described which allow its use for extended indications, which will be discussed in the next section. Inuoe et al. describe POEM using a mucosotomy at the 2 o’clock (anterior) position and performing the myotomy through the circular muscle layer leaving the longitudinal muscle layer intact . Several centers now favor the 5 o’clock (posterior) position with a full thickness myotomy which includes the longitudinal muscle [23, 24].
POEM can be broken down into eight steps: (1) Submucosal injection is performed with saline stained with indigo carmine, (2) Mucosotomy is performed along the right anterior wall of the esophagus in the 2 o’clock position (anterior myotomy), (3) Submucosal dissection is performed with hybrid knife or triangle-tip knife, (4) Submucosal tunnel is extended into the gastric cardia and a completed submucosal tunnel is seen, (5) Myotomy is initiated 2–4 cm below the site of mucosotomy, (6) LES myotomy is performed, (7) Complete full thickness myotomy is seen on withdrawal of the endoscope, and (8) Mucosotomy closed with endoscopic clips .
POEM is performed under general anesthesia with the patient in the supine position. The specifics will be described based on the author’s technique, which is consistent with anterior, circular muscle myotomy described by Inoue  and is currently the most favored technique among providers . Specific modifications for situations such as achalasia type III, sigmoid esophagus, and diffuse esophageal spasm will be discussed in detail later in the chapter.
Using a high-definition upper endoscope (GIF-180, Olympus, Tokyo, Japan), an initial mapping esophagogastroscopy is performed. CO2 is used for insufflation. The GEJ is identified and the distance from the top of the gastric folds to the incisors is recorded. The anterior and posterior orientations are defined using fluid meniscus, which will be posterior in the supine position and abdominal palpation.
Dissection of the Submucosal Tunnel
Once the mapping EGD is completed and orientation is confirmed, the endoscope is introduced with a transparent distal cap (M1-I 588, Olympus) fitted at its distal tip. An anterior location inside the esophageal lumen 10 cm above the GEJ and at the 2 o’clock position is chosen for initiation of the submucosal tunnel. Injection of normal saline mixed with indigo carmine into the submucosal space at the selected location is used to lift the mucosa away from the deeper muscular layers. An endoscopic injection needle (Carr-Locke 711811, US endoscopy, USA) is used for this injection (step1). A 2-cm mucosotomy is then made on the elevated mucosal cushion with a triangle-tip knife (KD-640L, Olympus), using electrocoagulation (ERBE, Tubingen, Germany) (Step 2). Once access to the submucosal space is achieved, the endoscope is advanced into the submucosal plane and dissected caudally to create a tunnel (step 3). Cautery and repeated injections of the saline mixture can be used to help define the planes and develop the tunnel. The tunnel is extended distally until the tip of the scope reaches 2 cm beyond the distance measured at the GEJ. The anterior orientation of the tunnel at the 2 o’clock position is confirmed by withdrawing the scope out of the submucosal tunnel and advancing through the lumen to the stomach. Using the retroflexed view presence of the blue-stained mucosa extending onto the lesser curvature confirms adequate length of the myotomy (step 4).
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Myotomy and Closure
Now that the length and location of the submucosal tunnel are confirmed, the scope is reinserted into the tunnel to perform the myotomy. The circular muscle fibers are identified and selectively incised using the triangle-tip knife, beginning 6–8 cm above the GEJ (step 5). The myotomy is extended distally 2 cm below the GEJ. The muscle fibers are hooked and pulled into the distal cap to avoid injury to deeper issue (step 6). Once the myotomy is completed, the scope is once again inserted through the lumen to evaluate the immediate effects of the myotomy (step 7). The esophageal mucosal incision is then closed using endoscopic clips (HX-201LR-135.A, Olympus) (step 8)  (Figs. 6.6 and 6.7).
Per oral endoscopic myotomy technique (S.N. Stavropoulos, Winthrop University Hospital, 2012). (a) Submucosal injection, and mucosal entry. (b) Creation of the submucosal tunnel. (c) Esophageal myotomy. (d) Lower esophageal sphincter and gastric cardia myotomy. (e) Closure of the mucosal incision