Sudden Cardiac Death: The Dangers of Rapid Heart Rhythms
Understanding Ventricular Tachycardia and Premature Ventricular Complexes
By Craig S. Cameron, MD, FCC, FACC
Sudden cardiac death is the leading cause of death in the United States. It accounts for more deaths than stroke, lung cancer, and breast cancer combined. When the normal electrical activation of the heart is interrupted by a rapid heart rhythm in the bottom chamber of the heart (ventricular tachycardia), sudden cardiac death occurs. Symptoms of ventricular tachycardia, VT, may include palpitations, light-headedness, dizziness, loss of consciousness, or seizures. VT is diagnosed using an electrocardiogram or heart monitor, and may indicate significant underlying heart disease.
Individuals with a prior heart attack and reduced “pump function,” are at particularly high risk for sudden cardiac death from VT.
For this reason, patients with VT usually require additional cardiac testing to assess the risk of sudden death and to determine treatment options. Such testing may include an echocardiogram, stress test, cardiac MRI, cardiac CT, or heart catheterization.
IMPLANTABLE CARDIOVERTER - DEFIBRILLATORS (ICDs)
The cornerstone of treatment for VT is to electrically shock the heart and reset its electrical activity. Unfortunately, most cases of sudden cardiac death progress too rapidly to allow sufficient time for emergency medical services to arrive and administer a life-saving shock. Thus, the implantable cardioverter-defibrillator (ICD) was developed and has revolutionized the prevention of sudden cardiac death. Current ICD models are capable of diagnosing and treating VT within seconds. While ICDs are highly effective at treating VT and saving lives, they do not address underlying heart disease and thus do not prevent VT from occurring. Furthermore, ICD shocks are painful and may result in reduced quality of life and psychological stress. ICD patients who have frequent VT often require either medications or a procedure called catheter ablation to reduce the burden of VT and likelihood of receiving electrical shocks.
ANTIARRHYTHMIC MEDICATIONS
Antiarrhythmic medications have demonstrated limited benefit for VT. Such “heart rhythm medications,” have not been shown to prevent sudden death and are only modestly effective at reducing VT burden and preventing ICD shocks. Additionally, antiarrhythmic medical therapy is often limited by drug interactions and extensive side effects. In some cases, antiarrhythmic medications may actually cause VT! Alternatively, catheter ablation is rapidly becoming a suitable and often superior therapy for preventing ICD shocks.
CATHETER ABLATION
Catheter ablation of VT is a minimally invasive procedure performed by an electrophysiologist (“heart rhythm doctor”) at specialized centers across the country, including Oklahoma Heart Institute.
It is performed in the electrophysiology procedure room under sedation or general anesthesia using a variety of tools which include X-ray fluoroscopy, intracardiac ultrasound, and 3-dimensional mapping systems. Small catheters are introduced from blood vessels in the groin and positioned within the heart. These catheters are then used to record the heart’s electrical activity and determine the source for the VT. Once identified, the abnormal tissues in the heart are targeted for radiofrequency ablation to eliminate VT.
The procedure generally lasts for 3-6 hours depending upon the number of abnormal electrical circuits identified and how easily they are eradicated. Overall, catheter ablation successfully reduces VT burden by more than 75%, thereby reducing ICD shocks. Despite the critically ill nature of many patients, VT ablation is generally well tolerated with a 1.5% risk of major complications.
Patients without heart disease who have VT are said to have “idiopathic VT.” Such patients are usually considered low-risk for sudden cardiac death and treatment is thus directed at controlling individual symptoms. Within this group of patients, isolated “extra beats,” from the bottom chamber of the heart called premature ventricular complexes (PVCs) are typically more common than actual VT. PVCs may cause palpitations, fatigue, shortness of breath, and lightheadedness. Individuals with very frequent PVCs (>10-20% of total beats on a 24 hour heart monitor) are at risk for developing a PVC-induced cardiomyopathy or “weakening of the heart’s pump function.” Thus, in addition to assessment of cardiac structure, such patients should also be considered for heart monitoring to quantitate their PVC burden. In some patients, lifestyle modification (e.g., caffeine reduction) is effective at reducing symptoms. Others require additional therapy with medications or catheter ablation.
As with VT in structural heart disease, antiarrhythmic medications have limited efficacy but may be useful in some patients. Idiopathic PVCs/VT tends to be a focal problem arising from predictable locations within the heart. As such, many of these patients are excellent candidates for catheter ablation. In the absence of significant heart disease, the success rate of catheter ablation for frequent PVCs or VT approaches 90%. Catheter ablation is therefore very effective at treating patient symptoms from idiopathic PVCs/VT. Also, weakening of the heart from a PVC-induced cardiomyopathy may be reversed by successfully ablating the culprit PVC.
CONCLUSION
In conclusion, sudden cardiac death is the leading cause of death in the United States and occurs as a result of ventricular tachycardia. Patients with VT should be assessed for underlying heart disease and risk of sudden death. ICDs are highly effective at preventing sudden death in at-risk individuals but do not address the underlying cause of VT. Thus, many patients with ICDs will ultimately require additional treatment to prevent ICD shocks. Likewise, many patients with idiopathic PVCs/VT may require treatment to address symptoms, or to prevent or reverse weakening of the heart’s pump function. Medications are often not effective or well tolerated in treating PVCs/VT. Thus, catheter ablation of PVCs/VT is offered at highly specialized centers such as the Oklahoma Heart Institute. Ablation is a safe and effective option to eliminate or significantly reduce VT in the majority of patients and should be considered early in the course of this disorder.