Unlike the disturbances of heart rhythm discussed elsewhere on this site (Supraventricular tachycardia and Atrial fibrillation) which tend to be relatively benign, if somewhat irritating to some patients, ventricular arrhythmias are potentially life threatening and should always be taken seriously.
As their names suggest, with ventricular tachycardia and ventricular fibrillation, the electrical activity driving the heart rhythm in these cases starts in the ventricles. In ventricular tachycardia (VT) the heart rate is fast but regular whereas in ventricular fibrillation (VF) the electrical activity is very rapid, uncoordinated and occuring simultaneously throughout the ventricles. In VT the patient response is variable and some patients will be able to maintain their cardiac output and blood pressure whereas others will feels very unwell or collapse. If the VT does not self-terminate or isn't stopped by medical intervention there is a significant risk that it will degenerate into VF. Patients experiencing VF will usually collapse unconcious within a few seconds as the uncordinated contractions of the muscle fibres are insufficient to produce a significant flow of blood out of the heart and the patient rapidly loses their blood pressure and blood flow to their brain. In these circumstances cardiac resuscitation with electrical shock treatment is usually required.
Below is an ECG showing Ventricular Tachycardia. It can be seen that the individual beats on the tracing are abnormally broad but that they all look the same. The heart rate is very fast at 220 beats per minute.
Below is an ECG showing Ventricular Fibrillation. Here the patient is in sinus rhythm and then there are four ventricular ectopics after which the heart rhythm suddenly degenerates into a very fast and irregular rhythm which is arising from the ventricle. (The patient collapsed but was rapidly resuscitated by an electrical shock delivered across the chest).
Thankfully these rhythm disturbances are relatively rare amongst the rhythm disturbances that we see but they may result from a variety of different causes. Some of these are listed below.
Coronary disease and heart attacks are relatively common. They probably account for the majority of cases of VF and VT. It is worth stressing that cardiac collapse early in the course of an acute heart attack, whilst a life threatening emergency in its own right, does not confer an increased risk of subsequent cardiac arrest in a resuscitated patient. In contradistinction patients who have VF or VT as a late complication of a heart attack should be investigated and treated appropriately as they do have a greater risk of sudden death from subsequent ventricular arrhythmias. Appropriate investigations may include coronary angiography to determine whether revascularisation (Angioplasty or Coronary Artery By-pass Grafts (CABG's)) can improve the blood supply to the ventricular muscle, specialised electrophysiological investigations (EP studies) to try to indentify any particularly irritable areas or the muscle and prolonged monitoring of the ECG to identify any potential heart rhythm disturbances.
Clearly the treatment of any given patient depends on any cause of the rhythm disburbance that has been identified.
If it seems clear that the principle cause is on-going ischaemia of the heart muscle (lack of an adequate blood supply) then Beta-blockers and/or nitrates may help in the immediate time course, however improving the blood supply by angioplasty or by-pass grafting is likely to be the most effective treatment longterm.
Occassionally a scar in the wall of the ventricle from a previous heart attack can be seen to be the place where the abnormal rhythm is starting. This may be able to be 'burnt out' using a special cardiac catheter (ablation therapy). Sometimes a scar can become stretched and bulge out from the wall of the heart when it is called an aneurysm. Occassionally these may need surgical removal (an operation that would normally carried out at the same time as coronary artery by-pass grafting).
If no cause is identifiable, or the cause is not amenable to cure (as with the cardiomyopaties) then treatment is directed at using drugs to reduce the chances of VT or VF occuring and devices to return the heart to a normal rhythm should the arrhythmias occur.
The drugs most often used are Beta-blockers and Amiodarone.
Often these will be backed-up by the insertion of a device called an Automated Implantable Cardioverter (AICD). These are similar to large pacemakers (and most have a pacing function as well). They are designed to detect ventricular arrhythmias and if the heart rhythm disturbance does not self terminate the device delivers an electric shock directly onto the inner surface of the heart to restore the normal heart rhythm. This is a complex area of treatment and if your cardiologist felt this was the right way forward for you he will discuss the merits of the treatment with you in depth. Further information about the indications for this type of treatment can be found in the guidance produced by the National Institute for Clinical Excellence (NICE). NICE Guidance on AICD's