Safety Study of Intranasal Etripamil for the Termination of Spontaneous Episodes of Paroxysmal Supraventricular Tachycardia (PSVT). NODE-302

Inclusion Criteria Patients who meet all of the following criteria will be eligible to participate in the study: 1. Male or female patients at least 18 years of age; 2. Signed the NODE-302 written informed consent; 3. Previously randomized in the NODE-301 study: * Received the study drug to treat symptoms the patient believed were consistent with an episode of PSVT during the NODE-301 study, irrespective of the study drug efficacy; OR * Did not experience an episode of PSVT or did not use the study drug at the time of the NODE-301 study completion; 4. Willing and able to comply with all aspects of the study; 5. Females of childbearing potential who are sexually active must agree to use an approved highly effective form of contraception from the time of signed informed consent until 30 days after the last administration of study drug. Females of childbearing potential should have a negative urine pregnancy test result at the Qualification Visit and at the Follow-up Visit(s), and must use an approved form of contraception between the 2 visits. Approved forms of contraception include hormonal intrauterine devices and hormonal contraceptives (oral birth control pills, Depo Provera®, patch, or other injectables) together with supplementary double barrier methods, such as condoms or diaphragms with spermicidal gel or foam; The following categories define females who are NOT considered to be of childbearing potential: * Premenopausal females with 1 of the following: 1. Documented hysterectomy, 2. Documented bilateral salpingectomy, or 3. Documented bilateral oophorectomy, or * Postmenopausal females, defined as having amenorrhea for at least 12 months without an alternative medical cause; and 6. Male patients, except those who are surgically sterile, must use an approved highly effective form of contraception during the 3 days after study drug administration. Exclusion Criteria Patients who meet any of the following criteria will be excluded from participation in the study, including but not limited to: 1. Evidence of new severe arrhythmia discovered since the NODE-301 Test Dose Randomization Visit, including those reported on the Cardiac Monitoring System (CMS) report of the outpatient PSVT event treated with the study drug in the NODE 301 study: d. Third-degree Atrioventricular (AV) block, Mobitz II second-degree AV block, or Wenckebach with bradycardia ≤40 bpm; e. Significant symptomatic sinus bradycardia heart rate (HR) ≤40 bpm or sinus pauses (≥3 seconds); f. Any significant ventricular arrhythmia (premature ventricular beats and couplets \[\>6 premature ventricular contractions per 45 seconds electrocardiogram (ECG)\] are considered significant); or g. Atrial fibrillation (event lasting longer than 30 seconds); 2. Any drug-related or procedure-related serious adverse event during the NODE-301 study; 3. Any severe adverse event (AE) in the NODE-301 study that was severe enough to preclude administration of etripamil NS 70 mg in the NODE-302 study; 4. Any new drug prescribed after the end of the patient's participation in the NODE-301 study that could lower blood pressure or decrease AV node conduction; 5. Systolic blood pressure \<90 mmHg after a 5-minute rest in sitting position at the NODE-302 Qualification Visit; 6. Any symptoms consistent with clinically severe hypotension such as presyncope, medically significant lightheadedness, syncope, nausea, or vomiting; 7. New therapy with digoxin, amiodarone, or any Class I or III antiarrhythmic drug added after the end of the patient's participation in the NODE-301 study; 8. New evidence of ventricular pre-excitation (e.g., delta waves, short PR interval, Wolff Parkinson-White syndrome) on the ECG since randomization in the NODE-301 study; 9. New symptoms of congestive heart failure defined by the New York Heart Association Class II to IV since randomization in the NODE-301 study; 10. New stroke since randomization in the NODE-301 study; 11. New evidence of a significant physical or psychiatric condition including drug abuse, which in the opinion of the Investigator, could jeopardize the safety of the patient, or impede the patient's capacity to follow the study procedures since randomization in the NODE-301 study; 12. New syncope since randomization in the NODE-301 study, especially if observed during the monitoring of the event treated in the NODE-301 study; 13. New evidence of hepatic dysfunction defined as alanine aminotransferase or aspartate aminotransferase \>3 × the upper limit of normal (ULN) or total bilirubin \>2 × ULN, unless due to Gilbert syndrome observed at the NODE-302 Qualification Visit; 14. New evidence of renal dysfunction as determined by an estimated glomerular filtration rate assessed at the NODE-302 Qualification Visit as follows: 1. \<60 mL/min/1.73 m2 for patients \<60 years of age, 2. \<40 mL/min/1.73 m2 for patients ≥60 and \<70 years of age, or 3. \<35 mL/min/1.73 m2 for patients ≥70 years of age; 15. Participation in any investigational drug or device study or the use of any investigational drug or device since the Final Study Visit in the NODE-301 study. Withdrawal Criteria Patient participation in this clinical study may be discontinued for any of the following reasons: * The patient withdraws consent or requests discontinuation from the study for any reason; * The patient took the study drug in both the NODE-301 and the NODE-302 studies for symptoms not associated with an episode of PSVT; * Occurrence of any medical condition, AE, or circumstance that exposes the patient to substantial risk and/or does not allow the patient to adhere to the requirements of the protocol; * Requirement of a prohibited concomitant medication and/or change in the use of chronic therapies, such as concomitant beta-blockers, calcium channel blockers, and medications that can lower blood pressure; * Patient failure to comply with protocol requirements or study-related procedures; * Termination of the study by Milestone or a regulatory authority; or * The patient self-administered a total of 11 doses of etripamil Nasal Spray 70 mg in the NODE-302 study. Patients who withdraw from the study after taking etripamil Nasal Spray 70 mg and had a Follow-up Visit will be required to undergo an Early Termination Visit. Patients who withdraw from the study and did not take etripamil Nasal Spray 70 mg will be required to undergo an Early Termination Visit. Patients who withdraw after taking the study drug but did not have a Follow-up Visit will be required to undergo a Final Study Visit.