CMS Updates NCD 310: What Billing Teams Need to Know About Microvolt T-Wave Alternans Coverage

CMS has issued a modification to National Coverage Determination (NCD) 310, which governs Medicare coverage for Microvolt T-Wave Alternans (MTWA) testing—a non-invasive diagnostic tool used to stratify patients at risk for sudden cardiac death (SCD). The updated policy, effective March 12, 2026, refines how MTWA testing coverage applies across different testing methodologies. If your practice bills for cardiac diagnostic testing or manages ICD candidacy workups, this policy deserves your immediate attention.

What Is Microvolt T-Wave Alternans Testing and Why CMS Covers It

MTWA testing measures minute fluctuations in the T-wave portion of an electrocardiogram—changes so small they're measured in microvolts. The clinical value is significant: these subtle electrical variations can identify patients who are at elevated risk for life-threatening ventricular arrhythmias and subsequent SCD.

The test plays a specific role in the ICD candidacy evaluation process. Within patient populations being considered for implantable cardioverter defibrillator therapy, a negative MTWA result can identify low-risk patients who are unlikely to benefit from ICD placement—and may actually experience worse outcomes with a device. That's a meaningful clinical distinction, and it's the foundation of why Medicare covers this test at the national level.

There are two primary MTWA testing methodologies recognized in this policy:

• Spectral Analysis (SA): A sensitive mathematical method that uses proprietary specialized electrodes to calculate minute T-wave voltage changes. Software analyzes these changes and generates a physician-interpreted report.
• Modified Moving Average (MMA): A temporal domain method that assesses T-wave alternans as a continuous variable along the complete ECG. The MMA method is performed using standard ambulatory ECG equipment—no specialized electrodes required.

The coverage determination treats these two methods very differently, and that distinction is the crux of what your billing team needs to understand.

CMS NCD 310 Coverage Rules: SA Method vs. All Other Methods

The national coverage structure under NCD 310 creates a clear two-tier framework:

Nationally Covered: Effective for dates of service on and after March 21, 2006, MTWA testing is covered by Medicare only when the Spectral Analysis (SA) method is used. This is the narrow, definitive national coverage determination.

MAC-Level Discretion for All Other Methods: Effective for dates of service on and after January 21, 2015, Medicare Administrative Contractors (MACs) acting within their respective jurisdictions may determine coverage for MTWA testing using all other methods—including the MMA approach. This means coverage for MMA-based MTWA is not guaranteed nationally and is entirely dependent on your regional MAC's local coverage determination (LCD).

This bifurcated structure is critical for billing. A claim for MMA-based MTWA testing that would be reimbursed under one MAC's jurisdiction could be denied under another's. Geographic variability in coverage is a real, tangible risk here.

What the Medical Necessity Criteria Require Under NCD 310

The nationally covered indication is specific: MTWA testing via SA method is covered for the evaluation of patients at risk for sudden cardiac death. That's the operative clinical criterion. Billing teams should ensure documentation supports this indication clearly—vague diagnostic justification will create vulnerability at audit.

There are no nationally non-covered indications specified in the current version of this policy. However, that does not mean blanket coverage applies. The coverage is restricted to SA methodology at the national level, and "all other methods" fall to MAC discretion—which in practice means you need to look up your MAC's LCD before billing MMA-based testing.

The policy does not mention prior authorization requirements, but that does not eliminate the possibility that your specific MAC or plan may require one. Always verify at the local level.

Affected Codes

This policy does not list specific CPT or HCPCS codes in its current version. Billing teams should consult the CMS Claims Processing Instructions referenced in the policy—specifically Transmittal 3265 (Medicare Claims Processing)—to identify the appropriate codes for MTWA claim submission. You should also check with your MAC directly for any locally assigned codes applicable to MMA-based testing under your jurisdiction's LCD.

Note: PayerPolicy monitors code assignments and cross-references as they are updated. If codes are added to this policy in a future revision, our version diff tools will capture the exact change.

The ICD Candidacy Connection: Clinical Context for Better Documentation

Understanding the clinical context behind this policy helps your billing and clinical teams build stronger documentation. MTWA testing sits upstream of ICD placement decisions. When a patient's MTWA result is negative using the SA method, that finding is clinically meaningful: it suggests the patient may not benefit from—and could be harmed by—an ICD.

This means MTWA is typically ordered as part of a broader arrhythmia risk stratification workup, often alongside echocardiography, Holter monitoring, and electrophysiology studies. Your documentation should reflect the specific clinical question being answered: is this patient a low-risk candidate who may not need an ICD, or does their risk profile indicate they would benefit from device therapy?

Documenting that clinical decision-making chain—patient risk factors, prior diagnostic findings, the clinical rationale for MTWA specifically—is what transforms a clean claim into an audit-proof one.

What Your Billing Team Should Do