Quick answers
- Does Michael P. Koumjian accept Medicare assignment?
- Yes. Medicare's clinician data says Michael P. Koumjian accepts Medicare assignment (the Medicare-approved amount as full payment for covered services), as of October 2, 2026. Ask the office to confirm before your visit.
- How many Medicare patients does Michael P. Koumjian see?
- In 2024, CMS data shows 131 Original Medicare patients and 1,126 services for Michael P. Koumjian. This counts Original Medicare only and measures volume, not quality.
- What is Michael P. Koumjian's NPI number?
- 1366403321. The NPI (National Provider Identifier) is the clinician's permanent federal ID; you can look it up in the official NPI Registry.
Medicare activity in 2024
Official CMS public-use data for Michael P. Koumjian, data year 2024 (released May 21, 2026). It covers Original Medicare (fee-for-service) patients only, not Medicare Advantage or other insurance. It shows volume, not quality or outcomes. CMS hides any count of 10 or fewer patients.
| Original Medicare patients | 131 |
|---|---|
| Services billed to Medicare | 1,126 |
| Different services or procedures | 105 |
| Participating Medicare provider | Yes |
| Average age of these patients | 75 |
Most frequent services
- Subsequent hospital care with moderate levelof medical decision making, if using time, at least 35 minutes (99232)266 services
- X-ray of chest, 1 view (71045)207 services
- Subsequent hospital care with moderate levelof medical decision making, if using time, at least 50 minutes (99233)132 services
- Initial hospital care with moderate level of medical decision making, if using time, at least 75 minutes (99223)117 services
- Ultrasound of heart, follow-up (93308)39 services
Chronic conditions among these patients
Share of this clinician’s Original Medicare patients with each condition, as published by CMS (it describes the patients, not the care given).
- High blood pressure75%
- High cholesterol75%
- Ischemic heart disease67%
- Heart failure67%
- Diabetes53%
- Atrial fibrillation49%
Hospitals where Michael P. Koumjian works
Medicare's Facility Affiliation Data lists Michael P. Koumjian at these hospitals (updated October 2, 2026). Each hospital page shows its address, phone, emergency services, Medicare rating and all its clinicians. Star rating and emergency services: Hospital General Information (CMS), data updated October 26, 2026.
- Grossmont HospitalLa Mesa, CA · Acute Care Hospital · Medicare rating: 4 of 5 stars · Emergency services: listed by Medicare · CCN 050026
- Loma Linda University Medical Center-MurrietaMurrieta, CA · Acute Care Hospital · Medicare rating: 2 of 5 stars · Emergency services: listed by Medicare · CCN 050770
- Southwest Healthcare Rancho Springs HospitalMurrieta, CA · Acute Care Hospital · Medicare rating: 3 of 5 stars · Emergency services: listed by Medicare · CCN 050701
Practice locations
Addresses where Michael P. Koumjian is enrolled with Medicare (CMS data updated October 2, 2026).
- 28062 Baxter RdMurrieta, CA 92563 (951) 290‑4000
- 4077 5th AveSan Diego, CA 92103 (619) 359‑6600
- 435 H StChula Vista, CA 91910 (619) 359‑6600
Group practices
Medicare enrollment lists Michael P. Koumjian as a member of this group (CMS data updated October 2, 2026).
- On Call Specialists Medical Group of San Diego Inc144 clinicians in the group
Specialties
- Cardiac Surgeryprimary
- Thoracic Surgeryalso
- Vascular Surgeryalso
Other cardiac surgeons in California
Clinicians with the same Medicare primary specialty in California — not a recommendation.
Other clinicians in On Call Specialists Medical Group of San Diego Inc
Medicare enrollment lists these clinicians in the same group practice — not a recommendation.
Clinician information
| Credential | MD |
|---|---|
| Medical school | Rutgers New Jersey Medical School |
| Graduation year | 1977 (49 years since medical school) |
| Gender (as listed) | Male |
| Medicare assignment | Accepts (Medicare-approved amount as full payment) |
| NPI (National Provider Identifier) | 1366403321 |
| Corrections | Report an error or suggest an update → |
Most corrections must be made at the source: clinicians update their NPI Registry record (NPPES) and their Medicare enrollment (PECOS); this page follows the next data release.
Sources
- Facility Affiliation Data — Centers for Medicare & Medicaid Services (CMS), data updated October 2, 2026, retrieved October 29, 2026
- Hospital General Information — CMS, data updated October 26, 2026, retrieved November 13, 2026
- National Downloadable File (Doctors and Clinicians) — CMS, data updated October 2, 2026, retrieved October 29, 2026
- Medicare Physician & Other Practitioners - by Provider — CMS, data year 2024, released May 21, 2026; Medicare Physician & Other Practitioners - by Provider and Service
- NPI Registry — U.S. Department of Health and Human Services (NPPES), the clinician’s official record
- Medicare Care Compare — official Medicare tool to look up clinicians